t(1;2)-Positive Localized Tenosynovial Giant Cell Tumor With Bone Invasion

Localized tenosynovial giant cell tumor (LTGCT) is one of the most common benign soft-tissue tumors of the foot. Although pressure erosion in the adjacent bone may be seen, intraosseous invasion of LTGCT is extremely rare. Recent molecular studies have identified the presence of pathognomonic translocation involving the colony stimulating factor 1 (CSF1) gene at 1p13.

We present an unusual case of LTGCT mimicking a malignant tumor on imaging. The patient was a 16-year-old woman with no history of trauma who presented with a 2-year history of a slow-growing, painless mass in the left fourth toe. Physical examination revealed a 2-cm, elastic hard, immobile, nontender mass. Plain radiograph showed a lytic lesion with a partially sclerotic rim in the proximal phalanx of the fourth toe. Computed tomography demonstrated an expansile lesion with plantar cortical destruction. Magnetic resonance imaging revealed a nodular mass with intermediate signal intensity on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. The mass had intense contrast enhancement. Complete excision of the mass was performed, and the bone defect was repaired with calcium phosphate cement. Cytogenetic analysis revealed a t(1;2)(p13;q37) translocation as the sole anomaly. Fluorescence in situ hybridization demonstrated the presence of CSF1 rearrangements.

Although extremely rare, LTGCT should be considered in the differential diagnosis of an intraosseous lesion near small joints, especially when seen in the toe.