Orthopedics

Case Report

A 53-year-old woman presented with a 6-month history of a right proximal medial calf mass that she reported to be increasing in size. The mass was painless at rest but caused the patient significant discomfort with activities of daily living and prolonged standing. She reported no history of trauma but had a history of arthroscopic right anterior cruciate ligament (ACL) cyst removal 11 years previously; no meniscal pathology was found at the time.

The patient initially presented to her primary care physician 1 month previously, where an ultrasound demonstrated an 8×3-cm septated cyst in the medial gastrocnemius. A 1.5-T magnetic resonance image with contrast revealed an 8.7×2.2×1.8-cm septated cystic mass originating from the popliteal bursa and dissecting into the medial gastrocnemius muscle with no edema or muscle enhancement (Figures 1, 2). Physical examination revealed a firm, nontender cystic mass in the right proximal medial calf with intact neurovasculature distally and full knee joint range of motion. No joint-line tenderness existed, and no joint effusion was appreciated.

Figure 1: Short T1 inversion recovery sequence coronal magnetic resonance image revealing an intramuscular cyst of the medial gastrocnemius muscle.

Figure 2: T2-weighted axial magnetic resonance image revealing an intramuscular cyst of the medial gastrocnemius muscle.

Because of the size, location, and symptoms of the lesion, the patient underwent surgical excision. The cyst was adherent to the gastrocnemius fascia and was dissected proximally in the muscle to a narrow neck, which was suture ligated (Figure 3). Pathology revealed a thin, fibrous, walled cyst with no lining epithelium consistent with a ganglion cyst.

Figure 3: Photograph of gross specimen.

Discussion

Ganglion cysts are thought to arise from the myxoid degeneration of connective tissue associated with a joint capsule or tendon sheath and, therefore, lack a true cell lining.⁷ The current article describes a histologically proven ganglion cyst arising at the gastrocnemius–semimembranosus junction and dissecting into the belly of the medial gastrocnemius muscle. The only other report of ganglia originating near this location is a series of 10 magnetic resonance imaging-suspected ganglia appearing at the head of the gastrocnemius, none of which were mentioned to dissect intramuscularly.⁴ The ganglia measured an average of 24 mm, and none were histologically proven to be ganglion cysts.⁴ The current article is unique because of the intramuscular dissection of the large ganglion and its origination at the semimembranosus–gastrocnemius junction. On magnetic resonance imaging, this made the distinction between Baker’s cyst and ganglion cyst difficult because Baker’s cysts are known to originate at the semimembranosus–gastrocnemius bursa. Previous literature has suggested that the origination of a cystic lesion at this location excludes ganglion cysts from the differential diagnosis.⁸ The current report contradicts this notion.

This finding is important because the potential exists to mistake a ganglion cyst of the knee joint for the more common Baker’s cyst. Orthopedists commonly refer to Baker’s cysts and ganglion cysts interchangeably. However, they are pathologically distinct entities with different treatment options. It has been reported that 82% of synovial cysts are associated with a meniscal tear, the most common involving the posterior horn of the medial meniscus⁹; thus, treatment is often aimed at treating the underlying meniscal damage. If they are large enough to be symptomatic, Baker’s cysts may be aspirated; however, they are rarely excised. Ganglion cysts have no underlying treatable pathology and have a high recurrence rate when aspirated. Therefore, surgical excision is the gold standard for management should a patient’s symptoms warrant intervention.^10,11

Conclusion

This article describes the previously unreported intramuscular dissection of a popliteal ganglion cyst into the gastrocnemius muscle. Given the possibility of misdiagnosis in similar cases, it is important for orthopedists to understand the distinction between cystic lesions of the popliteal fossa because of their different treatment options.