A Case of an Extraosseous Pretibial Ganglion Cyst

INTRODUCTION

Pretibial ganglion cysts are relatively uncommon. These can mimic a tumor. We report a case of extraosseous pretibial ganglion cyst and discuss Magnetic Resonance Imaging (MRI) features, etiology, and differential diagnosis.

CASE REPORT

A 49-year-old man presented with an anterior swelling on his right shin that had appeared over the past 6 months. There was no associated pain, but the lesion did vary in size. The patient was otherwise well and had no history of antecedent trauma or surgery. On examination, the lesion measured 7 cm by 5 cm, was fluctuant and had no signs of local lymphadenopathy. Lateral and anteroposterior (AP) radiographs showed no calcification or osseous abnormalities [Figure 1]. The pretibial subcutaneous lesion was of low signal on T1 and high on Short tau inversion recovery (STIR) sequences [Figure 2]. There was no communication between the lesion and the knee joint. Normal marrow signal was noted of the adjacent tibia, and there was no periosteal reaction. A differential diagnosis of myxoma and ganglion cyst was considered. A tru-cut biopsy was performed, and the specimen was evaluated histologically. The biopsy revealed the material to consist almost entirely of a mucoid acellular substance with a small fibrous connective tissue fragment at one side and no synovial lining. Based on clinical history, physical examination, radiology, and histological reports, a diagnosis of extraosseous pretibial ganglion cyst was made.

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Figure 1:

AP and lateral radiograph of knee does not show any calcification in the pretibial region.

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Figure 2:

Sagittal T1 (a), STIR (b), and axial STIR (c and d) showing pretibial extraosseous ganglion (arrow).

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DISCUSSION

Ganglion cysts are pseudocysts containing jelly-like fluid and lined by fattened cells. These usually arise from the joint or tendon sheath following extension of synovial fluid in to the adjacent soft tissues. Ganglion cysts in the pretibial region are extremely rare with few cases described in the literature. Of those reported, majority have been attributed as a rare complication of anterior cruciate ligament surgery.^[1-5] Maeseneer et al. had demonstrated communication between the knee joint and pretibial ganglion cyst on delayed arthrographic images.^[6] These can mimic a tumor due to its atypical location.

The initial suspicion in our case was of a malignant tumor and was, therefore, referred to our oncology services. Following the biopsy, the lesion was significantly decompressed. Unfortunately, the patient presented 3 months later with recurrence, which was discussed at our multidisciplinary meeting and subsequently excised. The presence of recurrence suggests and supports the hypothesis that these invariables have communication with the knee joint, which may be obliterated and difficult to delineate on non-arthrographic MR images.

Pretibial hematoma, juxtacortical chondroma, osteosarcoma, infection, and pretibial varices are some of the lesions that can mimic a pretibial ganglion. Pretibial hematoma can be of varied signal on MR depending on age of hematoma. Juxtacortical chondroma is hypo- to isointense on T1 and high signal on T2. Infection is associated with marked osseous and soft-tissue edema with or with intraosseous abscess depending on the stage of osteomyelitis. Osteosarcoma involves the metaphysis and is associated with marked periosteal reaction. The other differentials for pretibial lesions include granuloma annulare which is painless subcutaneous lesion in childeren that is low on T1 and heterogenous signal on T2. Cutaneous angioleiomyoma, soft-tissue sarcoma, and giant-cell tumors of the subcutaneous tissues are low on T1 and heterogenous to high on T2. Synovial sarcoma should also be considered which demonstrate heterogeneous signal on T2 with hemorrhage, calcification, and fluid levels. Rheumatoid nodule and Morel-Lavallee lesion are also in the differential. However a careful assessment of the lesion helps to clinch the diagnosis.

CONCLUSION

Pretibial ganglion should be considered while evaluating a pretibial lesion.