A 61-year-old truck driver was referred for a painless mass on the left ring finger that lasted for 1 year; the lesion began to expand aggressively during the last 3 months. It started at the finger base and gradually expanded to involve the entire finger, which markedly limited hand function (Fig. 1a). There was no precipitating factor, swelling elsewhere, or history of malignancy. The patient reported an unintentional weight loss of 15 kg without other constitutional symptoms.
An examination revealed a 10 x 10 cm circumferential mass on the left ring finger extending from the distal interphalangeal joint to the fourth metacarpal head. It was firm to hard in consistency and was multilobulated with an irregular surface. The mass was warm, non-tender and attached to the overlying skin with dilated veins. The little and middle fingers were splayed due to the mass effect. Sensation over the ring finger was reduced, but intact circulation.
A plain radiograph showed a large soft tissue mass of the left ring finger that displaced neighbouring fingers (Fig. 1c). There was extensive destruction of the proximal and middle phalanges with soft tissue calcification. Local magnetic resonance imaging (MRI) showed an expansile mass arising from the proximal phalanx with a soft tissue component occupying the adjacent web spaces (Fig. 1d). The mass showed heterogeneous isointense in T1W and T2W and enhancement post-contrast. There was a non-enhancing cystic area, which may represent a cystic component or necrotic area. An area of persistent hypointensity was observed on T1W, T2W, and blooming on GRE and may represent calcification. It eroded the fourth metacarpal head and infiltrated the adjacent lumbricals and interossei muscles. Computed tomography scan of the lung showed no evidence of lung metastasis. The clinical and radiological differential diagnosis at that point of time was chondrosarcoma or osteosarcoma.
A tissue biopsy showed a low-grade spindle cell lesion. Subsequently, the patient underwent rays amputation of the ring and small fingers and wound closure by means of a local ulnar-based flap originating from the small finger (Fig. 1b). Histopathological examination revealed an ill-circumscribed and destructive bone lesion composed of mostly uniform plump spindled cells that have an indistinct moderate eosinophilic to amphophilic cytoplasm. The intervening stroma was highly collagenized. No osteoid was seen. Thick fibrous septae were present in between the tumour cells. No significant nuclear atypia or mitosis was observed (Fig. 2). Tumour cells were focally positive for SMA but negative for desmin, EMA, BCL2, TLE-1, SATB2, STAT6, CK7, CD34, and B-catenin. The overall morphology was in favour of DF of bone. However, the surgical resected margin was involved with tumour cells. At 6 months of follow-up, there was no local recurrence and he had good overall hand function with acceptable hand grip strength (Fig. 3). Nevertheless, a long-term follow-up was necessary to evaluate for local recurrence.