Cover illustration © Jennifer E. Fairman
Tumors of the sacrum are rare. Metastases are the most common malignant tumors of the sacrum, derived from lung, breast, kidney, prostate, head and neck, gastrointestinal or skin (melanoma) cancers1,2; these will not be discussed further. Primary benign and malignant tumors of the sacrum may arise from bone or neural elements, or the bone marrow in cases of hematological malignancies. Ten percent of all benign tumors or pseudotumors involve the sacrum, including giant cell tumors (60% of cases), aneurysmal bone cysts (4%) and osteoblastomas. Six percent of all malignant bone tumors involve the sacrum, including chordomas (50% of cases), lymphomas (9%) and multiple myelomas (9%), Ewings sarcoma in children (8%), chondrosarcomas in adults, and osteosarcomas. Other benign and malignant tumors of the sacrum are exceptional.3
The clinical pattern depends on the anatomical location of the lesion within the sacrum, its extension, and whether it compresses or invades neighboring structures.4 Clinical examination is usually poor; sacral tumors usually remain clinically silent for a long time. The most common initial symptom of a sacral tumor is local pain due to its mass effect and compression. Occasionally, lower sacral tumors can grow large enough for their anterior portion to be palpated during a rectal examination4,5; however, no tumor has ever been observed to cross the presacral fascia and invade the rectum (Figure 1).6-8 Lateral extension of sacral tumors across the sacroiliac joints cause local pain at the joint.6-10 Invasion of the origin of the gluteus maximus and piriformis muscles leads to local pain and subsequently decreases hip extension and external rotation power.8
As nerve roots become increasingly compressed or infiltrated by the tumor, a multiradicular sensory deficit develops including radicular pain radiating uni- or bilaterally into buttocks, posterior thigh or leg, external genitalia, and perineum. At a later stage, motor deficit, and eventually, bladder/bowel and/or sexual dysfunction from anterior extension of the tumor into the presacral space is noted.4 A unilateral lesion to the S2 or S3 nerve root usually leads to mild or moderate bladder, bowel, and/or sexual dysfunction.4,11 A bilateral lesion of the S2 or S3 roots always results in complete bladder, bowel, and sexual dysfunction. Unilateral or even bilateral lesions of the S4 and/or S5 roots do not result in autonomic dysfunction, Although anatomical work has shown some S4 and S5 root contribution to bladder and bowel function.7,12
The sacrum is difficult to evaluate fully on radiographs because it is often obscured by overlying stool or bowel gas. Furthermore, the sacrum does not have a distinctive trabecular pattern that can be assessed for disruption. Thus, conventional radiography has a limited sensitivity and is only significant when it is abnormal showing the degree of osteolysis and sclerosis, and gross calcification or ossification within bone or adjacent soft tissue, or a pelvic mass. The presence of these signs requires further imaging evaluation by bone scintigraphy, computed tomography (CT) scan, or magnetic resonance imaging (MRI).13,14
Bone scan should be conducted to determine whether the lesion is polyostotic. If there are multiple lesions, the differential diagnosis is usually limited to metastases, multiple myeloma, Pagets disease, and vascular tumors.13 Positron emission tomography scan increases sensitivity and specificity of bone scintigraphy and appears to be a useful tool for detection of small bone lesions.15
Computed tomography is superior in showing bony details, soft tissue structures and calcifications. Lumbar CT scans usually ordered for sciatica of cruralgia must include S1 and S2 in the examination so that sacral lesions are not missed. Computed tomographyguided biopsy is particularly useful in the sacrum. If CT is substituted for MRI and there is a presacral soft tissue mass, both rectal and intravenous contrast should be administered to evaluate involvement of the pelvic structures. When possible, however, MRI is the imaging modality of choice to specify the diagnosis, tumor extent into the sacral canal, neurovascular involvement, and preoperative planning.13,14 Angiography is usually performed before preoperative embolization of hypervascular sacral lesions to reduce tumor vascularity.14,16
The differential diagnosis of sacral tumors is extensive, thus, biopsy should be performed in almost all cases. The minimally invasive nature of true-cut needle biopsy seems to be the most oncologically sound. A transrectal or transvaginal biopsy should not be performed in any case since it violates the containing membranes of presacral fascia and periosteum. The rectum or vagina may become seeded with tumor cells, thus making it necessary to resect these organs at the time of operation. In general, the surgeon who performs the definitive tumor resection should perform the biopsy or direct the biopsy procedure. Poorly planned incisional biopsies or incomplete debulking operations performed prior to referral to an orthopedic oncology center have been shown to increase the risk of local recurrence and metastasis.12
Benign Sacral Tumors
Common benign sacral tumors in children are sacrococcygeal teratomas (the most common), lipomas, dermoids, epidermoid cysts, and bone islands or enostoses.17-21 Congenital abnormalities such as spina bifida occulta, tethered cord, hairy nevi, dermal sinus tracts, and dimples are associated with tumors of the sacrum in children.5,19
Sacrococcygeal teratomas are rare congenital tumors that arise from pluripotential cells. Although usually (70%) benign, there is a tendency toward malignant transformation as the child gets older.17 Approximately 20% of sacrococcygeal teratomas are identified prenatally; 70% are identified at birth, and the remaining 10% are identified within the first year of life and usually present with intestinal obstruction. In adults, sacrococcygeal teratomas are rare and more commonly benign. On radiographs, the tumors are seen as an anteriorly and inferiorly protruding soft tissue mass, with amorphous, punctuate or spiculated calcifications. Computed tomography and MRI usually show a heterogeneous mixture of solid and cystic components.16 Most sacrococcygeal teratomas resections are performed via a posterior approach, although in one-third of the cases a combined abdominalsacral approach is required; the associated 5-year recurrence rate is approximately 10%.5
Bone islands or enostoses of the sacrum are usually asymptomatic but may be painful when large. Histologically, bone islands are lamellar compact bone with a Haversian system embedded within the medullary canal. They are distinguished from metastases or osteoid osteoma by bone scan that show normal or mildly increased uptake. On MRI, the lesion shows low signal intensity on all sequences.16,20,21
The most common benign sacral tumors in adults are giant cell tumors (13% of all sacral tumors), aneurysmal bone cysts, osteoblastomas, and schwannomas; osteoid osteomas, skeletal osteochondromas, chondromyxoid fibromas, nerve sheath, and meningeal tumors of the sacrum are rare.22-26
The sacrum is the third most common location for giant cell tumors after the knee and the radius.16,27-29 Giant cell tumors typically affect patients in the second to fourth decades, with a female predominance. Sacral giant cell tumors usually develop in an eccentric position, but commonly extend to involve both sides of the midline. There is usually a thin cortical rim, but the soft tissue mass can break through this rim; the mass is usually large before it is detected and may extend into the presacral space.2,13 Giant cell tumors of the sacrum have the propensity to cross the sacroiliac joints and intervertebral disks, which is unusual for many other spinal lesions and is a useful distinguishing feature of giant cell tumors.16 Although generally classified as a benign tumor, 5% to 10% of giant cell tumors have been reported to be malignant. Many of the malignant lesions are thought to be related to previous radiation therapy. Furthermore, giant cell tumors occasionally metastasize to the lung although the primary lesion is considered histologically benign.13
The standard treatment for giant cell tumors is wide excision or aggressive curettage followed by adjuvant phenol, hydrogen peroxide, liquid nitrogen or argon beam therapy, embolization, and bone grafting or cementation; cryosurgery or radiation therapy are also possible (Figure 2).11,30-33 If complete resection cannot be achieved, the recurrence rate may be as high as 50%.9,22,29 Preoperative embolization may prove palliative and/or curative because of the high vascularity of giant cell tumors in cases in which the lesion cannot be resected or in which the disease is refractory to other treatments; in these cases, the risk of local recurrence is equal to 31% at 10 years and 43% at 15 and 20 years.9,33 In appropriately selected patients, sacrectomy is a valuable procedure to effect local tumor control and overall patient survival.31,32
Three percent of aneurysmal bone cysts arise from the sacrum.2 Aneurysmal bone cysts typically affect patients younger than 20 years, with a slight female predominance.21 Sacral aneurysmal bone cysts originate in the sacral ala but often extend to involve the vertebral bodies. Computed tomography and MRI often demonstrate fluid levels caused by hemorrhage with sedimentation. However, this is not a pathognomonic sign because other lesions such as giant cell tumors, telangiectatic osteosarcomas, osteoblastomas, and schwannomas may also contain fluid levels.13,14 The preferred treatment method is complete excision, if possible. Incomplete excision is associated with a high recurrence rate of approximately 14% within 18 months of treatment. Surgery may be supplemented with embolization and radiotherapy.23
Forty percent of all osteoblastomas occur in the spine; of these, 17% arise in the sacrum.2 Osteoblastomas typically affect young adults, with a male:female ratio of 2:1. The tumors usually originate in the posterior elements of the spine, but 42% extend into the vertebral bodies. Three radiographic/CT patterns of osteoblastomas have been described. These include a lytic pattern surrounded by sclerosis with or without central calcification, the most common pattern of an expanded lesion with multiple small calcifications and a peripheral sclerotic rim, and the most aggressive pattern of bone destruction and infiltration of surrounding soft tissues, often with a matrix. Osteoblastomas should be excised. The lesions recur in 10% to 15% of cases, but the rate approaches 50% in the more aggressive pattern. Malignant transformation of osteoblastoma to osteosarcoma with metastases has also been reported.13,21
Osteoid osteomas of the sacrum represent <2% of sacral tumors.3,24 En bloc resection or radiofrequency ablation is possible with low recurrence rate.1,34,35 Cavernous hemangiomas are the most common benign tumors of the spine, but only exceptionally involve the sacrum.36
Skeletal osteochondromas or exostoses, although relatively frequent in the appendicular skeleton, only 1% to 4% occur in the spine, predominantly the cervical, thoracic, or lumbar regions. The incidence rises to 7% to 9% in patients with multiple hereditary exostoses. Less than 0.5% of osteochondromas of the spine occur from within the sacrum.3,37 Neurological symptoms are not common because most do not protrude into the spinal canal or neural foramina.38 The imaging appearance is typical showing continuity of normal marrow and cortex extending from normal underlying bone, without destructive change or soft-tissue mass.13 Marginal excision of a sacral osteochondroma usually constitutes definitive treatment. Complete excision of the cartilaginous component is recommended to decrease the likelihood of local recurrence. However, the cartilaginous cap is more difficult to excise completely if the tumor protrudes into the neural foramina or spinal canal.37
Chondromyxoid fibroma is a rare benign tumor of the sacrum.39 Differential diagnosis should include chondrosarcoma, chordoma, and giant cell tumor. Surgical excision of the affected area or curettage and bone grafting is the treatment of choice for chondromyxoid fibroma. Radiation therapy should only be considered for the rare surgically inaccessible tumor because of post-irradiation complications.39
Nerve sheath tumors may arise from the sacral nerve roots and include schwannomas and neurofibromas. The most common nerve sheath benign sacral tumors are the giant sacral schwannomas; the mean diameter of these tumors is approximately 10.5 cm. There is often anterior displacement of the pelvic organs but usually evidence of invasion. The larger, dumbbell-shaped tumors with intradural and extradural components typically cause enlargement and erosion of the neural foramina and sacral destruction. They may also cause scalloping of the vertebral bodies.16,40 Cyst formation, hemorrhage, and necrosis are relatively common in giant sacral schwannomas; unlike neurofibromas, schwannomas tend to be encapsulated. En bloc resection is the treatment of choice. Although difficult because of their size and the presence of critical sacral nerve roots, most can be resected completely, and recurrence is rare.40,41 Malignant nerve sheath tumors (neurofibrosarcomas or malignant schwannomas), may also occur. These tumors are associated with neurofibromatosis type 1 as they usually arise from pre-existing neurofibromas.16
Neuroblastomas and ganglioneuroblastomas represent the most common solid malignant tumor in children younger than 5 years; 5% of them occur in the pelvis. Most are located at the anterior surface of the sacrum and may extend into the sacral foramina and then into the spinal canal.42 Ganglioneuromas represent the mature benign form of neuroblastic tumors and are observed in older children, adolescents, or young adults. They are slowly growing tumors that can sometimes involve bone, particularly the sacrum.43 Sacral ependymomas arise from ependymal cells of the terminal filum, expand the sacral canal, and are usually of the myxopapillary type or metastases from a primary tumor of the central nervous system, causing an erosive mass of the sacrum (Figure 3). Ependymomas occasionally occur outside the central nervous system and are called extraspinal ependymomas; these are found predominantly in the sacrococcygeal region during childhood.44,45
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Figure 3: Coronal CT scan (A) and T2-weighted sagittal MRI (B) of the sacrum of a 62-year-old woman with a sacral ependymoma. The tumor invades from the sacral canal.
Meningeal tumors of the sacrum include meningoceles, sacral Tarlov meningeal cysts and lumbosacral meningiomas arising in the spinal canal or a sacral foramen. Anterior or posterior sacral meningocele, myelomeningocele, and lipomyelomeningocele occur as a mass attached to the conus medullaris or terminale filum protruding through a defect in the sacrum or in a context of sacral agenesis.46 Sacral Tarlov meningeal cysts are abnormal meningeal dilatations in the spinal canal or sacral foramina that may or may not communicate with the subarachnoid space.47-49
Malignant Sacral Tumors
The most common malignant tumors of the sacrum are chondromas, multiple myelomas, Ewings sarcomas and primitive neuroectodermal tumors (PNET). Primary lymphomas, osteosarcomas, chondrosarcomas, angiosarcomas, fibrosarcomas, carcinoid and amyloid tumors of the sacrum are rare.50-66
Chordomas are the most common primary malignant tumor of the sacrum, and the most common tumor of any type involving the sacrum, representing 40% of all primary sacral neoplasms.28,50 The majority of sacral chordomas occur in the sacrococcygeal region. Chordomas occur almost twice as frequently in men compared to women and are uncommon in individuals younger than 40 years.51
Chordomas are slow growing and often displace but do not invade the rectum and/or the bladder. Metastasis is usually a late event.51 Osseous expansion and midline or paramedian lytic destruction extending to the inferior part of the sacrum and coccyx with amorphous intratumoral calcifications and a large soft tissue mass that extends into the presacral space are the typical imaging findings of sacrococcygeal chordomas. The osteolysis is well circumscribed without an osteosclerotic rim, but sometimes associated with bulging of the cortex. A solid tumor with cystic areas is seen in approximately 50% of cases.2,13,14,16 Dedifferentiated chordoma is a rare variant that is clinicopathologically analogous to dedifferentiated chondrosarcoma. The sarcomatous component of dedifferentiated chordomas may demonstrate more aggressive biological behavior and a higher propensity to metastasize.52
Primary treatment for chordomas is wide resection. The prognosis relates to its completeness and the violation of the tumor margins at the initial surgery. The surgeon should not hesitate to sacrifice sacral nerve roots at the time of surgery if it is necessary to obtain en bloc resection. Otherwise, continued tumor growth or local recurrence will lead to even more severe neurological dysfunction. Total sacrectomy for chordomas involving S1 has been reported.32,53-55 If incomplete resection, adjuvant radiation therapy may be performed, however, its efficacy has been debated.6,10,12,56-58
Local recurrence is the most important predictor of mortality in patients with chordomas and it is clearly related to the extent of initial resection7,8,10,12,51; local recurrence of sacral chordomas results in high morbidity rates and it is associated with a 21-fold increased risk of tumor-related death.12 High local recurrence rates for sacral chordoma treated with traditional surgical debulking and radiation therapy have been reported.12 Results with brachytherapy techniques for recurrent sacral chordoma have been reported in small numbers of patients.59 Newer methods of radiation delivery, such as charged-particle irradiation and high linear energy transfer therapy are yet to be determined. Chemotherapy has been of little value in the management of chordomas.10,57 Metastases eventually develop in 5% to 43% of patients; metastases may be found in the liver, lung, regional lymph nodes, and in unusual sites such as the peritoneum, skin, and heart.50,56
Multiple myeloma is the second most common primary malignant neoplasm of the sacrum. Its incidence peaks in the sixth and seventh decades, and the male:female ratio is 2:1.28 The earlier solitary form, plasmacytoma, affects younger patients when compared with multiple myeloma. Lesions tend to be larger than those of multiple myeloma. They are typically osteolytic and grossly expansile, with poorly defined margins, and an associated soft tissue mass. Plasmacytomas eventually progress to multiple myeloma after intervals of up to 10 to 15 years.13,16,61
Lymphomas are the third most common primary malignant tumors of the sacrum.28 They predominantly affect men in their second and third decades of life. Lymphomas can cause aggressive bony destruction, although they tend to extend to the soft tissue leaving the underlying bones intact.13,16,62 Three imaging signs, although nonspecific, are suggestive of lymphomas. These include the intensity and extent of uptake on bone scan, the massive bone marrow invasion on MRI despite normal radiographic findings, and the large soft tissue mass with no visible cortical lesion on CT. This highlights the importance of pursuing investigations (particularly bone scintigraphy and MRI) in patients with persistent pain despite their having no detectable abnormality on conventional radiography.14
Ewings sarcoma and PNET represent the fourth most common primary malignant tumors of the spine.28 Within the spine, the sacrum is the most common site of involvement.21 The age range for Ewings sarcoma is 5 to 30 years, with 75% occurring in the first 2 decades. The male:female ratio is 3:1. On radiographs, these lesions cause permeative osteolysis, expansion and sclerosis.60 Paraspinal soft tissue masses and extradural space involvement are prominent features.21,60 Some cases of sacral Ewings sarcomas may present a predominant soft tissue mass, extending to pelvic structures or to the spinal canal, with limited osteolysis.14
Histologically, Ewings sarcoma and PNET are composed of small round cells with large irregular sheets divided by septa. Immunohistochemical studies are needed to distinguish Ewings sarcoma from PNET, with the latter being characterized by neural differentiation.16,21,60 Primary treatment for Ewings sarcoma and PNET is chemotherapy and radiation therapy. Many patients, however, require decompressive surgery and stabilization. Unfortunately, these lesions are associated with the worst prognosis when they occur in the sacrococcygeal region, with local control being accomplished in only 62.5% and long-term survival in only 25%.21
Osteosarcomas account for 4% of primary malignant tumors of the sacrum. Many of the osteosarcomas of the sacrum are secondary to Pagets disease.28 Sacral chondrosarcomas, fibrosarcomas and angiosarcomas are unusual.63 A 2% incidence of primary and secondary chondrosarcomas of the sacrum has been reported (Figure 4).3 Most of sacral fibrosarcomas arise from a pre-existing lesion, usually previously irradiated bone, Pagets disease, infracted giant cell tumor or fibrous dysplasia.3
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Figure 4: Sagittal T1-weighted (A) and coronal T2-weighted MRI (B) of the sacrum of a 48-year-old man show a primary chondrosarcoma of the S1.
Carcinoid tumors of the sacrum are rare. These tumors derive from endocrine gastrointestinal amine precursor uptake and decarboxylation cells, and are typically located in the appendix, ileum, lung, and rectum and can cause the carcinoid syndrome. Carcinoid tumors in the sacrum/presacral space can be metastatic or associated with a rest of enteric tissue.64,65 Bladder and/or bowel dysfunction has been described as clinical presentation, but not the carcinoid syndrome.65 Sacral amyloid tumors usually occur in the context of multiple myeloma or plasma cell dyscrasia.66
Surgical Treatment of Sacral Tumors
The surgical goals in the management of sacral tumors are to remove the tumor completely with clear margins and to maximize postoperative function. A radical surgical approach such as partial or total sacrectomy, with sacrifice of sacral roots, is often warranted to achieve total resection with clear margins.7 Various sacrectomies have been described depending on the tumor location, extent, and histology. In general, sacrectomies can be categorized either as partial or total. Decision regarding partial or total sacrectomy for en bloc resection can be made after radiological evaluation and bone biopsy.
Total sacrectomy is indicated when a malignant or aggressive benign lesion involves the proximal sacrum.53,54,67,68 Partial sacrectomy includes transverse, sagittal, or combination. Lateral sacral tumors that lie entirely to one side of the sacrum are treated by sagittal partial sacrectomy. According to the transverse axis and sacroiliac joint involvement, sacral tumors are distinguished into high midline lesions above S3 without lateral invasion of a sacroiliac joint, high lateral lesions above S3 with sacroiliac joint invasion, and low midline lesions below S3. Lateral lesions with sacroiliac joint involvement are treated by sagittal sacrectomy. High or low midline tumors without sacroiliac joint involvement are treated by transverse sacrectomy (Figure 5).14 Sagittal partial sacrectomies also are frequently done as part of an extended hemipelvectomy for tumors of the medial iliac wing that involve the sacroiliac joint or sacrum.54,69
Techniques for en bloc resection of sacral tumors were pioneered in the 1960s and 1970s.12,51,70 With the advent of more aggressive surgery, local tumor control has significantly improved. These technically demanding procedures require multidisciplinary (neurosurgery, surgical and orthopedic oncology, and plastic surgery) involvement. Combined dorsal and ventral exposures have been described, and the use of the transpelvic vertical rectus abdominis myocutaneous flap for the reconstruction of large sacral defects has significantly reduced problems with wound breakdown.51,70-75
The general approaches to sacral tumors include anterior, posterior, and combined approaches for large aggressive sacral tumors extending to S1 or the lumbar spine, or the pelvis. Anterior approaches include either transabdominal or retroperitoneal exposures, whereas posterior approaches involve sacral laminectomy and partial posterior sacrectomy. A less common route is the perineal approach for distal benign sacral tumors.76
Sacral laminectomy lends itself well to pathological entities originating within and largely confined to the sacral canal because of the ease and clarity with which the neural elements and their coverings are exposed. Treatment of cysts and neurogenic tumors such as schwannomas, neurofibromas, and ependymomas is the foremost indication for this approach. The majority of these tumors are benign, and cure is effected by total resection of the tumor and its capsule. Intimate involvement with the still functional sacral roots is the most frequent barrier to total extirpation of such tumors. Sacral laminectomy as the primary exposure is less well suited to lesions originating outside the sacral canal or extending significantly into the pelvis via the neural foramina or by direct sacral invasion.77,78
Posterior sacrectomy is performed to treat tumors of the sacrum below the level of the sacroiliac joints. It allows management of the presacral extension and en bloc resection of the tumor with a circumferential margin of the uninvolved tissues. The indications for posterior sacrectomy include malignant bone tumors of the sacrum that are more likely to present with a presacral mass, tumors whose superior limit can be reached on digital rectal examination, and smaller lesions of the middle and distal sacrum not yet requiring resection above the level of the sacroiliac joint.77,78
Although posterior sacrectomy is as high as the first sacral segment, it is a less attractive approach for higher sacral resections. It is impossible to dissect the soft tissues of the upper presacrum accurately when using this approach, thereby considerably increasing the risk of major vascular injury, inadvertent entry into the rectum, or violation of the tumor capsule during attempts to osteotomize the anterior sacrum and sacroiliac joints from behind. In addition, posterior sacrectomy should not be used in cases of primary rectal involvement.77 These difficulties are best addressed by combining the techniques of posterior sacrectomy with an anterior approach for lesions requiring amputation above the level of the sacroiliac joints.78
The indications for a combined anteroposterior approach include extensive vascularity of the tumors, primary proximal sacral tumors engaging the lumbosacral junction (in particular the S1 endplate), and disease that penetrates the anterior pelvic fascia. Proceeding with an anteroposterior approach in these scenarios ensures optimal hemostasis and adequate exposure for en bloc resection when indicated.79 An alternative to a conventional transperitoneal anterior approach is the extensile ilioinguinal approach, which permits simultaneous visualization of the anterior and posterior sacrum when combined with a posterior midline approach.80
Localio et al70 were the first to popularize a synchronous abdominosacral approach for resection of sacral tumors. They favored the lateral decubitus position, thereby enabling simultaneous anterior and posterior exposure without the need for patient repositioning. They suggested that synchronous abdominosacral resection resulted in less blood loss than sequential resection. However, although this technique can be used to expose the sacrum anteriorly and posteriorly simultaneously in the lateral position, it is more difficult to expose both of them well. The lateral position also complicates soft tissue reconstruction or mechanical stabilization often integral to the success of these procedures.70
Bowers81 described a sequential anterior and posterior approach for high sacrectomy.Transabdominal exposure was used to gain control of the hypogastric vessels and enable a safer posterior sacrectomy. The anterior approach improves the surgeons ability to dissect the tumor accurately from the rectum because it can be accomplished under direct vision rather than by blind finger dissection. Furthermore, should the rectum be involved by tumor either as a consequence of direct extension or because of seeding from an injudicious transrectal biopsy procedure, it can now be freed for en bloc resection with the sacral specimen. This is impossible from the posterior approach alone.
The anterior or intraperitoneal procedure of the combined approach for total sacrectomy is performed with the patient positioned supine. A longitudinal midline incision from 2 to 3 cm above the umbilicus to the symphysis pubis is made, and the retroperitoneal tumor is reached transperitoneally or extraperitoneally depending on the extent and type of tumor. After the bowel has been packed off, the posterior parietal peritoneum is opened unilaterally, the ureters are identified and the iliac vessels dissected bilaterally. If the rectum is to be spared, it is mobilized off the tumor capsule ventrally after incision of the retrorectal peritoneal reflection. The tumor capsule is outlined circumferentially. Internal iliac and middle sacral arteries and veins are ligated along with any tumor vessels; both external iliac arteries should be preserved. The iliac veins are mobilized medially and laterally during the anterior sacral osteotomy. The peritoneal investment and the periosteum are incised caudally as far as the greater sciatic notch, and the cortex can be scored anteriorly to facilitate subsequent completion of the osteotomy from behind. The sacral foramina are visualized anteriorly, and serve as landmarks to guide the anterior sacral osteotomy. Lateral dissection of the sacral ala allows identification of the lumbar trunk (L4-L5) of the lumbosacral plexus. The sacroiliac joint is identified lateral to these nerve roots, and a bilateral partial anterior sacroiliac osteotomy is performed using a chisel and/or drill. The L5-S1 disk is exposed and removed along with the anterior aspect of the annulus fibrosus. If the anterior sacral nerve roots are not obscured by the tumor, they are divided at their foramina and cut bilaterally. Waxing the osteotomy cuts helps reduce bleeding and improves visibility. The vascular structures and the rectum are separated from the lumbar vertebrae and the sacrum using a gauze or a flexible thin silastic sheath. The abdominal skin is closed in layers and a drain is placed.78
The posterior procedure of the combined approach is performed with the patient positioned prone via a posterior midline exposure. The posterior incision extends from L2 to beyond the coccyx, leaving skin, subcutaneous tissue, and muscle in place over the sacrum to facilitate en bloc resection. Any skin compromised by tumor, biopsy, radiation-induced change, or prior surgery should also be excised with the specimen. Violation of the tumor capsule must be avoided at all costs. The posterior iliac crest, greater sciatic foramina, and sciatic nerves are exposed bilaterally, as are the L3-L5 spinous processes, facet joints, and transverse processes. An L5 and subtotal S1 laminectomy exposes the thecal sac and cauda equina at this level. The sacral nerve roots are then divided, and the thecal sac is double sutured. The remaining disk of L5-S1 is removed completely. The sacrospinalis muscles are sectioned transversely, and the posterior sacroiliac ligament attached to the ilium is incised. Laterally, the gluteal musculature is transected, leaving a cuff attached at its sacral origin. This uncovers the piriformis muscles that are, in turn, divided at their musculotendinous junction. The superior gluteal vessels and nerves are found at the upper border of the piriformis and the inferior gluteal vessels; the sciatic, pudendal, and posterior femoral cutaneous nerves are found exiting the pelvis at its lower edge. These should be identified carefully and preserved whenever possible. If rectal resection is not planned, the caudal border of the specimen is freed by division of the anococcygeal ligament just proximal to the anal sphincter. The sacrotuberous ligament is detached from the ischial tuberosity, and the coccygeal muscles are cut. The sacrospinous ligament is detached by an osteotomy cut across the base of the ischial spine. If the rectum is to be included with the specimen, the anus is dissected circumferentially and the levator musculature divided. The soft tissue dissection is finished, and the field is prepared for completion osteotomies from behind. The osteotomy along the ilium can enter into the sciatic notch either medial or lateral to the ischial spine. The sacrum is now free and can be lifted out of the wound dorsally. Sacral nerve roots are divided as they exit the sacrum, protecting the sciatic nerves from injury. The entire sacrum along with the neoplasm is then excised en bloc.78
After total sacrectomy and spinopelvic reconstruction, the huge sacrectomy defect can be closed by the transpelvic vertical rectus abdominis myocutaneous flap based on the inferior epigastric vessels, the reversed latissimus dorsi flap, the gluteal flaps, the gracilis flap, or microvascular free flap reconstruction. If the transpelvic vertical rectus abdominis myocutaneous flap is going to be used, it is prepared before anterior skin closure.
Reconstruction of the posterior pelvis and reestablishment of spinopelvic stability is challenging.32,68,72,79,82-84 Many types of partial sacrectomies are well tolerated without the need for reconstruction. In general, sacral tumors below S1 are structurally stable and seldom require reconstruction; since the conventional S2-S3 partial sacrectomy does not disrupt the sacroiliac articulations, lumbopelvic stability is preserved. Sacral tumors at the S1 level, however, alter the biomechanics at the lumbosacral junction and may therefore require stabilization.5,68,85,86 If lumbopelvic reconstruction is not performed, patients should be maintained in a hip spica cast for prolonged periods, with ambulation dependent on scar tissue.32
Indications for lumbopelvic stabilization include total sacrectomy, partial sacrectomy involving >50% of sacroiliac joint on each side, and sagittal and high transverse partial sacrectomy that essentially obliterate the sacroiliac articulation unilaterally or bilaterally and destabilizes the lumbopelvic segment.54,69,82
When assessing instability at the lumbosacropelvic region, one must consider the anterior column, axial load transmission to the pelvis, posterior tension band, and pelvic ring competency. Although all of these factors are essential to biomechanical stability, a strong anterior column is the most important factor. The absence of a strong anterior column results in increased stress placed on the posterior elements via cantilever forces, up to 80% impairment of normal axial load transfer and weight bearing, and up to a 50% reduction in pelvic strength. The anterior column may be deemed unstable if the disease process extends to 1 cm below the sacral promontory and extends to more than two-thirds of the sacral endplate.82 In this instance, repair of the anterior column is mandated to restore axial load transmission from the spinal column to the pelvis. Following sacrectomy, pelvic ring competency must be ensured for a stable lumbopelvic construct by a transiliac bar.79
The common goal of most reconstruction techniques is to stabilize the spine to the pelvis by achieving a solid lumbopelvic fusion (Figure 6). This has been attempted through the use of various combinations of screws, wires, bars, and plates. The earliest spinopelvic constructs of the 1980s involved a combination of sacral bars and Harrington rods, sacral rods or AO plates and Harrington rods or Cotrel-Dubousset instrumentation, Steinmann pins and Cotrel-Dubousset rods, dynamic hip screws, internal spine fixators, and transpedicular Schanz screws.55,68,85,87 Techniques further evolved in the 1990s to include use of the Galveston rod fixation with iliac screws and transiliac rods,68,77,88-90 the sacroiliac joint and the iliac-sacral screw fixation,91,92 the posterior iliosacral plating and screw fixation,92,93 and custom-made prosthesis.32,83
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Figure 6: Wound closure was done using the transpelvic vertical rectus abdominis myocutaneous flap (D). At 6-months postoperatively, solid lumboiliac arthrodesis and no evidence of local recurrence is observed (E).
The sacroiliac joint screw technique is suitable for a partial sacrectomy with preservation of approximately 50% of the sacroiliac joint. The iliac-sacral screw fixation technique is recommended after partial sacrectomy. This technique has been shown to be associated with significantly less failure than the Galveston technique. It can be used in conjunction with hooks or pedicle screws in the lumbar spine.91
The Galveston rod technique was first described for the treatment of neuromuscular scoliosis with pelvic obliquity.88,94 Later, it has been used for reconstruction following total sacrectomy, for bypass stabilization of the ilium to the lumbar spine. The rod was used in conjunction with sublaminar wiring of the lumbar spine. These constructs, however, do not provide substantial torsional stability or resistance to extension.95 Compared with sublaminar devices, pedicle screws provide significantly increased rigidity. When attached to the rods and cross-linked the medially directed screw creates a triangular effect, which greatly increases the screw pullout resistance, increases torsional stability, and allows a short-segment fusion.89,90,96,97 A potential drawback is the relative difficulty of rod contouring. Preformed rods can be obtained, which can decrease intraoperative time.78
Previous methods of lumbopelvic reconstruction were meant to allow surgeons to stabilize the lumbar spine relative to the ilia with instrumentation, and to bridge the gap between the ilia and the most caudal vertebral body with nonstructural bone graft. The bone graft did not provide immediate structural continuity between the spine and the pelvis, and had multidirectional loading during its progression toward an anticipated fusion. The current generation of instrumentation used in lumbopelvic reconstruction is the pedicle screw-rod construct. This instrumentation is easier and more rigid than previous constructs, and offers the ability to place fixation screws independent of the connecting bar construct. Once the screws are safely placed, the bars can be contoured to mate with the screws and are secured to create a fixed-angle construct.69
Margulies et al98 reported that the placement of long 7- to 8-mm diameter threaded screws into the iliac wing could be a technically easier method for lumboiliac fixation than the Galveston technique. After placement of the screws in optimal position, they are linked to the spinal rod independently. A cross-linked bar between the rods makes the construct more rigid and stable. Sung et al99 reported the successful results of combining structural allograft and screw fixation through the ilium to bridge the osseous defect after subtotal or total removal of sacrum in 2 patients.
Gokaslan et al68 described a complex lumbopelvic reconstruction and fusion using a modified Galveston L-rod technique. Segmental fixation of the lumbar spine is done from L3 down by pedicle screws and a bilateral liaison is established between the lumbar spine and the ilia by using the Galveston L-rod technique. The pelvic ring is then reestablished by a threaded rod connecting left and right ilia. Autologous (posterior iliac crest) and allograft bone is used for fusion, and a tibial allograft strut is placed between the remaining ilia.68 The same authors modified their construct for spinopelvic reconstruction following en bloc resection of a giant sacral chordoma. In their updated construct, the axial load is transmitted to the pelvis via the transiliac bar and via a cross connector to the rod connecting the iliac screws. Pedicle screws are inserted bilaterally at L3-L5 along with rods attached to the screws and connected to a transiliac bar via L-shaped connectors. Bilateral iliac screws are connected by a rod. Three cross-connectors are used; from one lumbar rod to another, from the bar connecting the iliac screws to the cross-connector between the lumbar rods, and from the bar connecting the iliac screws to the transiliac bar. A femoral allograft is used to bridge the defect between the ilia, and is secured to both the transiliac bar and the rod connecting the iliac screws by titanium wires. In this way, the axial load is distributed between 2 pelvic fixation points in 2 planes.54,100
Salehi et al101 performed lumbopelvic reconstruction by posterior segmental fixation with lumbar pedicle screws and a Farsi iliac bolt system for fixation to the ilium and connected this to the rod affixed to the pedicle screws. They supported the anterior column by a pyramesh cage traversed by a transiliac bar.101 Doita et al102 reported on lumbopelvic reconstruction by using the ISOLA transpedicular and iliac screw system and a sacral rod for fixation. The transverse sacral rod was connected to the vertical rods by 2 rod connectors. The authors concluded that this construct provides greater stability around the horizontal axis of the spinal column and prevents rotation around this axis. Kawahara et al84 described a novel lumbopelvic reconstruction technique consisting of both posterior and anterior instrumentation. The posterior instrumentation consists of L3-L5 pedicle screws connected to iliac screws via a rod; the anterior instrumentation consists of 2 pedicle screws inserted into the inferior endplate of L5 and a sacral rod connected to both sides of the pelvis through these screws. According to the authors, this model is associated with a low risk of instrument failure and loosening after total sacrectomy. Mindea et al79 described reconstruction of the lumbosacropelvic junction by using a pyramesh cage-induced axial support with transfer of spinal axial load via a transiliac bar, and posterior segmental reconstruction with pedicle screws and iliac bolts for immediate lumbopelvic stabilization.
Dickey et al69 presented a new technique of lumbopelvic reconstruction that uses pedicle screw and rod constructs in conjunction with a triangular fibular structural graft construct placed along the natural vectors of force transmission from the spine to the hips. According to the authors, this reconstruction technique places structural graft along the force transmission lines between the base of the most caudal remaining vertebra and the hip joints bilaterally. The triangular construct that is created in this manner results in compression at the proximal and distal docking sites of the structural graft and the host bone, which is a more favorable loading condition for bony healing to occur.
Infection, hemorrhage, wound healing complications, and neurological dysfunction are problems associated with sacrectomy. Care must be taken to protect the visceral structures, including the ureters, intestines, and rectum. If the rectum is adherent to the tumor, an elective colostomy is necessary. If a colostomy is to be performed, it is usually conducted after the sacrectomy and reconstruction have been completed to lessen the risks of wound infection.78 To facilitate wound healing, various types of muscle flaps and incisions can be performed. Different methods to overcome excessive hemorrhage have been proposed, including the application of polymethylmethacrylate, fluid nitrogen, phenol, hydrogen peroxidase, hot water, or hemostatic substances such as gauzes, fibrin glue, or an omentum flap onto the bed of the tumor, and cryosurgery.11,103,104 Protection of vascular structures using meticulous dissection techniques, and ligation of the median sacral, internal iliac, and iliolumbar arteries is necessary to cut off the vascular supply to the sacrum and tumor. Cell saver autotransfusion cannot be applied to malignant tumors.105
Sacrifice of the sacral nerve roots produces varying degrees of sensorimotor, bladder, bowel, and sexual dysfunction. Patients with amputations distal to S3 generally have limited deficits, with preservation of sphincter function in the majority and some reduced perineal sensation. Sexual ability may also be inhibited. The highest variability in functional results is seen for transverse resections of S2-S3 (including removal of 1 to all 4 roots of S2-S3). There is seldom any relevant motor deficit; however, many patients have saddle anesthesia and a significant reduction in sphincter control.73 Patients with bilaterally preserved S2 nerve roots will retain bowel and bladder function; in those in whom only 1 S2 nerve root is preserved bowel and bladder function will likely be lost.5 Preserving both S1 nerve roots is important for normal gait and foot plantar flexion. Sectioning of the S1 roots may result in clinically relevant motor deficits (walking with external support), and almost uniformly results in total loss of sphincter control and sexual ability. Unilateral resection of sacral roots leads to unilateral deficits in strength and sensitivity; however, sphincter control may be either preserved or only partially compromised.75,106
If one-third of the sacroiliac joint and the associated ligamentous structures are rejected, the pelvic ring is weakened by approximately 30%. Resections between S1 and S2 cause loss of stability in approximately 50%. Weight bearing is safe for patients after sacral resection, as long as >50% of the sacroiliac joint (corresponding to at least the upper half of the S1 segment) remains intact.82
Primary complete resection of sacral tumors may be difficult because of their proximity to neural and vascular structures. In these cases, radiation therapy may be useful. For sacral metastases, radiation therapy may be the initial treatment of choice, whereas in some cases of primary sacral tumors, conventional radiation therapy may be used in conjunction with surgery as adjuvant treatment, for palliation of pain, prevention of pathological fractures, and halting progression of or reversing neurological compromise of the lesion.107 Because of the concern for malignant transformation, radiotherapy is generally not recommended in the initial management of benign tumors. However, radiation therapy has been performed for aggressive osteoblastomas, aneurysmal bone cysts, and giant cell tumors of the sacrum.23,108
Local control rates with radiation therapy for aggressive recurrent giant cell tumors have been reported to range from 70% to 90% in series involving radiation doses of 35 to 68 Gy. The recommended dose for conventional radiotherapy of these lesions is 40 to 45 Gy.107,109 The addition of radiation therapy in subtotally resected sacral chordomas prolonged the disease-free interval to 2.12 years compared with 8 months without radiotherapy. Radiation doses of 30 to 50 Gy are indicated for palliation with minimal risks.10 Cummings et al110 reported no differences in survival, duration of symptomatic response, and progression-free survival in a heterogeneous group of patients with sacral chordomas who underwent 50 to 60 Gy radiation therapy compared with conventional fractions to ,50 Gy or by a hyperfractionated regimen of 44 Gy delivered in 1 Gy fractions, 4 times daily for 14 days.
The role of stereotactic radiosurgery is a well established, safe, and effective treatment for various benign and malignant intracranial lesions. However, current frame-based stereotactic radiosurgery techniques such as the GammaKnife and LINAC-based systems do not have the capability of treating lesions below the foramen magnum because precise localization can be achieved only by fixation of stereotactic frames to the patients skull. Most of these techniques involve a head frame device that is attached by 4 screws to the patients skull for precise targeting of radiation to the tumor.111,112
Currently, a unique image-guided frameless stereotactic radiosurgery system known as the CyberKnife (Accuray, Inc, Sunnyvale, California) has been developed for the treatment of tumors of the sacrum that are not candidates for open surgical intervention or conventional external-beam radiation therapy, or as an adjunct to surgery. The system consists of a lightweight LINAC mounted on a robotic arm. Real-time imaging tracking allows for patient movement tracking with 1 mm spatial accuracy.107,113-116 Because of the spatial precision with which the CyberKnife can administer radiation, it is theoretically feasible to administer a tumoricidal radiation dose to the sacral tumor in a single treatment as has been the case for intracranial tumors.115-118
Unlike conventional radiation therapy in which a full dose is delivered to both the vertebral body and the spinal cord or cauda equina, the CyberKnife can deliver a high-dose single fraction to the target tissue while sparing most of the adjacent neural elements, thus significantly reducing the possibility of radiation-induced myelopathy or injury to the nerve roots. This is the main advantage of stereotactic radiosurgery for treatment of many spinal and sacral tumors.118
Stereotactic radiosurgery has been found feasible, safe, and effective for the treatment of both benign and malignant sacral lesions. The major potential benefits of radiosurgical ablation of sacral lesions are relatively short treatment time in an outpatient setting and minimal or no side effects. In a study,118 eighteen patients with primary and metastatic sacral tumors were treated using the CyberKnife Image-Guided Radiosurgery System. Three patients underwent radiosurgery for disease progression documented on serial follow-up imaging after receiving conventional external-beam radiation therapy. The tumor types in these 3 patients included bladder carcinoma, colon carcinoma, and melanoma. Two patients underwent radiosurgery as their primary and only radiation treatment for the tumors. The tumor types in these 2 patients were spindle cell sarcoma and an S-1 schwannoma. Treatment duration was between 30 and 120 minutes; all patients underwent the procedure in an outpatient setting. Tumor dose was maintained at 12 to 20 Gy (mean 15 Gy). The maximum intratumor dose ranged from 15 to 25 Gy (mean 18 Gy). Tumor volume ranged from 23.6 to 187.4 mL (mean 90 mL). All patients successfully completed the treatment without any complications during a mean follow-up of 6 months. At 1-month follow-up, axial and radicular pain improved in all 13 patients who were symptomatic prior to treatment. No tumor progression has been documented on follow-up imaging.118
Embolization is a useful adjuvant therapy in the management of sacral tumors. Typically, Gelfoam, PVA particles, alcohol embolizing emulsions, coils, tissue adhesives, ethanol, and microfibrillar collagen are used for embolization.119-125 If a vascular sacral lesion is suspected based on presentation and imaging, then preoperative angiography should be performed to characterize the vascular anatomy and to determine if the lesion would be amenable to embolization. Of note, sacral tumors may have significant collateral circulation, and tumor neovascular recruitment may induce the formation of an extensive lumbosacral collateral arterial network. Therefore, knowledge of these interconnections is imperative prior to performing an embolization procedure.120
Once the decision is made to proceed with embolization, it is important to determine if a proximal arterial occlusion or embolization within the lesion is necessary. Occlusion at the level of the medium-sized vessels allows collateral circulation to restore flow immediately after embolization. Occlusion of smaller vessels results in slower constitution of collateral pathways, but there is a potential for tissue ischemia. Selective delivery of an embolic agent is desirable to minimize unwanted collateral vessel occlusion and subsequent tissue infarction and necrosis.119 If selective vascular delivery is not possible, then direct percutaneous puncture techniques may be necessary to obtain a selective embolization placement.121
The timing of preoperative embolization is important. Generally, it is recommended that embolization should be performed as close as possible to the time of surgery. Typically, minimal blood loss occurs when surgery is performed within 24 to 48 hours after embolization.121-125 When Gelfoam is used for preoperative embolization, surgery should be performed within 24 hours to prevent recanalization.125
Embolization techniques have been used to treat benign lesions such as giant cell tumors and aneurysmal bone cysts, malignant, and metastatic lesions of the sacrum as an adjuvant therapy to surgery or radiation therapy. Giant cell tumors and aneurysmal bone cysts may respond to embolization as a primary and definitive treatment alternative to surgery.9,26,33,120,124 Overall, the recurrence rate after embolization for giant cell tumors and aneurysmal bone cysts lesions is low; recurrence can be managed with repeated embolization. Serial embolization of these lesions is typically performed at 4- to 6-week intervals until symptomatic improvement occurs or the tumors vascularity disappears.33 Other benign lesions of the sacrum that can be treated with embolization include aggressive osteoid osteomas, osteoblastomas, hemangiomas,34,126 sacral meningiomas,127 and presacral schwannomas.128 Because of its variable vascularity, angiography is useful in determining if a sacral chordoma is hypervascular and evaluating whether embolization would be beneficial preoperatively.120 Hypervascular metastatic sacral tumors can also be treated with preoperative embolization.129
Ischemic neuropathy is a potential complication of any pelvic embolization that can result in motor and sensory deficits in the pelvis and lower extremities. Additionally, the sacral plexus of nerves can be injured. Therefore, care must be taken to identify and avoid embolization of the neurovascular anatomy. Rectal ischemia can result from superior hemorrhoidal artery embolization. Any embolization of sacral tumors may result in injury to non-targeted tissue including muscle infarction, injury to the skin, or injury to the colon or other organs.120
The management of tumors of the sacrum is challenging. Radical resection through partial or complete sacrectomy can prolong the overall survival of patients with primary malignant or aggressive benign tumors. However, establishing immediate stability through spinopelvic reconstruction is necessary for early ambulation and preservation of the quality of life, especially for patients with a limited life expectancy. Modern radiation therapy and stereotactic radiosurgery have the potential to reduce complications by including higher treatment doses with lower volumes of normal tissue within treatment fields. Embolization can be used effectively to treat hypervascular benign and malignant tumors of the sacrum as an adjunct to surgery.
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Drs Mavrogenis and Papagelopoulos are from the First Department of Orthopedics, Dr Patapis is from the Third Department of Surgery, and Dr Kostopanagiotou is from the Second Anesthesiology Department, ATTIKON General University Hospital, Athens University Medical School, Athens Greece.
The material presented in any Vindico Medical Education continuing education activity does not necessarily reflect the views and opinions of Vindico Medical Education or Orthopedics. Neither Vindico Medical Education or Orthopedics nor the authors endorse or recommend any techniques, commercial products, or manufacturers. The authors may discuss the use of materials and/or products that have not yet been approved by the US Food and Drug Administration. All readers and continuing education participants should verify all information before treating patients or using any product.
Correspondence should be addressed to: Panayiotis J. Papagelopoulos, MD, DSc, Athens University Medical School, 4 Christovassili St, 15451, Neo Psychikon, Athens, Greece.