Radiologic Case Study
- May 2006 - Volume 29 · Issue 5:
A 10-year old boy presented with progressive, unrelenting knee pain.
1: AP radiograph of the right knee of a 10-year old boy.
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Answer to Radiologic Case Study
Aggressive Periosteal Reaction and Codmans Triangle Marginal to an Osteosarcoma of the Distal Femur
An anteroposterior radiograph of the distal femur in a 10-year-old shows abnormal sclerosis of the distal femoral metaphysis with a cloud-like appearance (Figure 1). There is vague mineralization of the medial soft tissues. In addition, there is a triangular periosteal bone formation proximally called a Codmans triangle. Findings are consistent with aggressive periosteal reaction secondary to metaphyseal osteosarcoma.
Figure 1: AP radiograph of the right knee in a 10-year-old boy shows abnormal trabecular replacement with cloud-like matrix at the distal femoral metaphysis consistent with osteosarcoma. Subtle soft-tissue matrix extends medially from the cortex. In addition, abnormal periosteal reaction is shown at the proximal medial margin with abrupt cutoff, forming a triangular density consistent with Codmans triangle.
Recognition and differentiation of various patterns of periosteal reaction are invaluable tools in generating a comprehensive differential diagnosis of musculoskeletal lesions. The structure of the periosteum covering the surface of bone varies with age. In infants and children there are two well-defined layers, an inert outer fibrous connective tissue layer and an inner osteogenic layer. The periosteum in the immature skeleton is thick, tough, and vascular with a well-developed osteogenic layer. The childs periosteum is loosely attached to the diaphysis and metaphysis but firmly attached to and reinforces ligaments, tendons, the perichondrium of the physis, and adjacent secondary ossification center. In adults, the periosteum is thin, has little vascularity, and is more firmly attached to the underlying cortical bone by collageneous Sharpeys fibers. The two layers are not as well defined in adults, but the inner osteogenic layer is present and maintains the capability of forming bone.
The inner osteogenic periosteal layer can produce new bone when lifted by hemorrhage, infection, or neoplasm due to intraosseous disease or stimulated by extraosseous disease. In children, the thick, vascular, loosely attached periosteum with a well-developed osteogenic layer responds more rapidly to stress, thus leading to a more exuberant and extensive periosteal new bone formation compared with adults.
Periosteal new bone formation can be a marker of, and may be the first sign of, bone disease. In addition, the appearance of periosteal new bone is an indicator of the relative aggressiveness or indolence of the underlying disease process. The two major categories of periosteal reaction are continuous and discontinuous new bone formation. Careful analysis of the periosteal new bone formation as demonstrated by radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) is one important factor in the recognition and differential diagnosis of disease.
Continuous New Bone Formation
Simple periostitis is common. This is the least complicated pattern, with delicate elevation of the periosteal membrane from the cortical surface and subsequent formation of a single curvilinear band of new bone that is elevated from the cortex centrally but is continuous with cortical bone proximally and distally. Both benign and malignant processes can produce simple periostitis,1 although new bone >1 mm thick typically has a higher probability of being benign.2,3 Early on, there is minimal mineralization so that the radiographic finding is subtle, as in the case of an evolving fracture (Figure 2) or hematogenous osteomyelitis. It may take up to 2 weeks for the new bone to mineralize sufficiently to be visible on radiographs.4 This type of reaction may also be physiologic after birth and is found in 50% of newborns (Figure 3).5 Occasionally, the delicate layer may be dramatically displaced from the host bone as seen in Caffeys disease (most notably in the mandible, clavicles, and scapulae) (Figure 4)6-8 or scurvy (most notable in the long bones).
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Figure 2: Oblique radiograph of the right tibia and fibula shows delicate periosteal reaction (arrows) at the proximal fibular shaft in this 14-year-old with an evolving bowing fracture of the fibula. Incompletely visualized is operative reduction of a subacute midshaft tibial fracture.
Lamellated or onion skin periosteal reaction is similar to simple periosteal elevation, except with multiple layers of continuous new bone formation.1 The separate layers of new bone are the result of alternating phases of disease activity and quiescence. Initially, the periosteum is elevated and forms a single layer of new bone. After a quiescent period, the periosteum is again elevated and forms a second separate layer of new bone. Further repetitions result in an increasing number of contiguous layers. Classically, this pattern is seen in Ewings sarcoma (Figure 5),4-6 but the same pattern can less often result from other malignancies and also infection.8,9 Marrow-infiltrating diseases (eg, leukemia) may also manifest a lamellated pattern. Occasionally, acute osteomyelitis results in layered periosteal elevation, especially in intermittent or partially effective antibiotic therapy.
The delicate single layer of lamellated new bone eventually is visible on radiographs, but it may be more easily seen on CT, where a thin calcific line parallels the cortex (Figure 6A). However, with CT, the underlying process may not be delineated in the early stages of disease. Alternatively, MRI is not only sensitive for identifying periosteal new bone, which appears as a relatively high signal reactive layer sandwiched between a thin signal void periosteal perimeter and the signal void cortex (Figure 6B), but it also is more sensitive than CT for demonstrating underlying bone abnormalities such as bone marrow edema associated with osteomyelitis and tumoral replacement.
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Figure 3: AP radiograph of the left humerus in a 1-month-old infant shows delicate periosteal reaction (arrows) at the distal diametaphysis consistent with physiologic new bone of infancy. Figure 4: Oblique radiograph of the left forearm in this 4-month-old infant shows exuberant, continuous new bone formation at the ulna (arrows) greater than the radius. In this case, the diagnosis is Caffeys disease or infantile cortical hyperplasia. Figure 5: Oblique radiograph of the mid/distal humerus in this 18-year-old shows abundant continuous but lamellated new bone (arrows) at the humeral shaft, marginal to a Ewings sarcoma.
Over time, the periosteal reaction continues to evolve and develop with variable outcome. In some cases, the underlying irritating process resolves and the host bone remodels and incorporates the new bone completely, without significant residua or focal cortical thickening.
If the underlying pathologic process is indolent, slow continuous new bone formation can result in fusion of multiple laminae or a homogenous, thick band of new bone contiguous with the subperiosteal cortex. This is the most indolent type of new bone formation, and is almost always associated with a benign process such as osteomyelitis, Langerhans cell histiocytosis, benign neoplasms, and healing fractures.4 The pattern can be seen with metastases but rarely with malignant primary bone neoplasms.
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Figure 6: This 8-year-old boy was diagnosed with vertical insufficiency fracture of the tibia. Axial CT image with bone windows shows continuous periosteal new bone (arrows) at the posteromedial shaft of the tibia due to a vertical insufficiency fracture (A). Axial T1-weighted spin echo image following infusion of contrast shows the enhancing white layer of active osteogenic layer sandwiched between the black line of elevated periosteum (arrows) and black cortex. Intense bone marrow edema with minimal soft-tissue enhancement supports an osseous etiology (B).
The radiographic appearance of subacute and chronic new bone will vary depending on when imaging is acquired, with gradual deposition of calcium and formation of trabeculae (Figure 7). The time interval until new bone remodeling occurs depends on the type of underlying process stimulating bone formation, the success of treatment, and the health of the host bone.
The active phase of evolution may not be seen on imaging and initial radiographs may show thick, dense periosteal layering over the cortex. Radiographically, the pattern may be smooth in character or have an undulating course. The cortex usually remains discernable and the underlying bone may otherwise be intact. Therefore, other radiographic features must be observed to discern etiology. For example, continuation of the periosteal bone onto the epiphyses associated with phalangeal involvement is more commonly associated with pachydermoperiostitis (Figure 8).6 Another classic manifestation of solid periosteal reaction is hypertrophic osteoarthropathy, which is benign, but can be a herald of malignancy of the chest or abdomen (Figure 9).10
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Figure 7: With time, periosteal new bone may show increasing mineralization associated with healing, as in this case of a 3-year-old girl being treated for osteomyelitis. Mortise view of the left ankle shows very subtle periosteal reaction (arrows) overlying permeative bone destruction associated with osteomyelitis (A). Mortise view two weeks later shows signs of early healing with increasing density of the periosteal reaction (B).
Figure 8: AP radiograph of the left forearm shows dense layering new bone at the radius and ulna with overall increased bone diameter in this patient with pachydermoperiostitis.
Neoplasm also may induce this form of periosteal reaction. Although not entirely reliable, dense mineralization of new bone usually indicates a more indolent tumoral process. The dense, chronic bone formation marginal to a highly irritative osteoid osteoma (Figure 10) is classic, while the new bone at the metaphysis marginal to an epiphyseal chondroblastoma is surprising but characteristic.11 Less commonly, malignant neoplasm such as chondrosarcoma can induce this more indolent, chronic-appearing cortical thickening and layered bone (Figure 11).
Discontinuous New Bone Formation
Discontinuous periosteal new bone usually is indicative of a more actively evolving process, with benign and malignant considerations. Patterns include the Codmans triangle, thin linear opacities perpendicular to the bone (hair-on-end), and spiculated linear opacities fanning out from the bone (sunburst).
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Figure 9: This elderly adult has dense periosteal new bone at the distal femoral diametaphyses due to hypertrophic osteoarthropathy. AP radiograph of the knees shows the layering new bone (arrows) at the distal femoral metaphyses, although the underlying cortex remains discernible (A). Corresponding axial T1-weighted spin echo image of the distal left femur also demonstrates the periosteal elevation (arrows) with subjacent bright, fatty attenuation layer consistent with chronic, non-reactive nature (B).
The basis of the Codmans triangle is initially simple, continuous, periosteal new bone. However, when the underlying pathology progresses rapidly enough, the central periosteum is elevated and new bone is destroyed leaving only a shard of adjacent periosteal new bone intact. This forms a triangle with the underlying cortex.4 Figure 1 illustrates the resultant triangular segment of periosteal bone produced by an underlying osteosarcoma, although other malignancies including Ewings sarcoma and fibrosarcoma may produce similar findings. Subperiosteal pus in osteomyelitis occasionally produces a Codmans triangle (Figure 12).
Figure 10: Lateral radiograph of the proximal left forearm in this teenager shows dense, reactive new bone at the dorsal ulnar shaft with a diagnosis of osteoid osteoma.
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Figure 11: AP radiograph of the left hip in this 75-year-old man shows dense periosteal new bone (arrows) and cortical remodeling marginal to an underlying chondrosarcoma. Figure 12: AP radiograph of the left first metatarsophalangeal joint in this 44-year-old woman shows extensive bone and joint destruction in the setting of fulminate osteomyelitis. A Codmans triangle (arrow) is seen at the medial first metatarsal.
The spiculated type also indicates fast biologic activity.12 Spiculated periosteal reaction is a result of a disturbance in the reparative phase that follows periosteal elevation. The rapid growth rate of the tumor or other pathologic process prevents confluent maturation of cell elements in the subperiosteal space into bone matrix. Instead, matrix deposits along Sharpeys fibers that support the periosteum and maintain relationship to the host bone cortex, and along periosteal vessels.1,4,9 Long, slender spicules are seen emanating from the cortex overlying malignancy such as an osteosarcoma (Figure 13). One specific pattern of spiculated bone is called a sunburst pattern since the mineralization radiates outward from a center point at the cortex (Figure 14). The implications of the general spiculated pattern and the sunburst pattern are similar.
Periostitis represents a physiologic response to stress from either benign or malignant processes and can be the result of both intra- and extra-osseous pathologies. Patterns of periosteal new bone formation do not delineate malignant from benign processes, since a malignant bone tumor and florid osteomyelitis can produce an equally aggressive periosteal new bone pattern. However, the type of periosteal new bone reflects the relative aggressiveness or indolence of the underlying process, similar to different types of bone destruction that range from geographic to permeative. Therefore, careful analysis of the pattern of periosteal reaction is one vital element to determining an appropriate differential diagnosis.
Figure 13: Underexposed lateral radiograph of the left knee in this young adult shows spiculated new bone (arrows) at the distal femoral metaphysis, superficial to an osteosarcoma. Figure 14: AP radiograph of the base of the right first metatarsal in this 51-year-old man shows sunburst new bone at the lateral base of the first metatarsal, reactive to an underlying osteosarcoma.
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- Lodwick GS. Solitary malignant tumors of bone: the application of predictor variables in diagnosis. Semin Roentgenol. 1966; 1:293-313.
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- Kwon DS, Spevak MR, Fletcher K, Kleinman PK. Physiologic subperiosteal new bone formation: prevalence, distribution, and thickness in neonates and infants. AJR Am J Roentgenol. 2002; 179:985-988.
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- Restrepo S, Sanchez AM, Palacios E. Infantile cortical hyperostosis of the mandible. Ear Nose Throat J. 2004; 83:454-455.
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- Greenfield GB, Schorsch HA, Sholnik A. The various roentgen appearances of pulmonary hypertrophic osteoarthropathy. AJR Am J Roentgenol. 1967; 101:927-931.
- Brower AC, Moser RP, Kransdorf MJ. The frequency and diagnostic significance of periostitis in chondroblastoma. AJR Am J Roentgenol. 1990;154:309-314.
- Reeder MM. Bone, joints, and soft tissues. In: Reeder MM, ed; Felson B. Reeder and Felsons Gamuts in Radiology. 4th ed. New York, NY: Springer-Verlag; 2003:314-324.
Drs Kim-Gavino, Lomasney, and Demos are from the Department of Radiology and Dr Ryan is from the Department of Orthopedics, Loyola University Medical Center, Maywood, Ill.
Reprint requests: Terrence C. Demos, MD, Dept of Radiology, Loyola University Medical Center, 2160 S First Ave, Maywood, IL 60153.