Teaching Case

An 11-year-old adolescent girl presented with swelling of the left little finger for one year. It was gradually increasing in size. There was no assosciated pain. On local examination, there was a circumferential swelling of the left little finger involving metatarsophalangeal as well as proximal interphalangeal joints. The swelling was non-tender on local examination.

Radiograph of left hand (Figure 1) revealed, lytic destructive expansile lesion involving proximal phalanx of left little finger with adjacent soft tissue component and no evidence of matrix mineralization.  Posteroanterior chest radiograph (Figure 2) revealed scattered patchy tissue opacities in bilateral upper lung zones. MRI of left hand (Figure 3a & b &c) revealed, expansile lytic lesion of proximal phalanx of the little finger with extensive circumferential cortical breach, extraosseous soft tissue encasing and displacing flexor and extensor tendons. There was involvement of adjacent proximal interphalangeal and metacarpophalangeal joint causing marked skin surface and soft tissue bulge. The lesion was hypointense on T1-weighted image (Figure 3a), isointense on T2-weighted image (Figure 3c) and showed heterogenous post-contrast enhancement with surrounding inflammation (Figure 3b).

Tuberculous dactylitis is an uncommon form of extra-pulmonary tuberculosis involving the small bones of the hand or the foot. The bones of the hands are more affected than the bones of the feet. Radiographic features of cystic expansion of the short tubular bones have led to the name of “Spina Ventosa” for tuberculous dactylitis of the short bones [1] As underlying bone is destroyed, a cystlike cavity forms and the remaining bone appears to be ballooned out. (“wind-filled sail” [2]. Tuberculous dactylitis mainly occurs through lympho-hematogenous spread during primary infection. Children aged 6 years and below accounts for 85% of cases [3]. However, even in the pediatric age, tuberculosis of the short tubular bones like phalanges, metacarpals or metatarsals are quite uncommon after the age of 5 years, once the epiphyseal centres are well established [4] The first line imaging modality of choice is a plain x-ray. Fusiform soft tissue swelling and periostitis are the most common radiographic findings.  The absence of sequestration and the presence of diffuse osteopenia distinguish tuberculous infection from pyogenic infection. CT scan features include bony sclerosis and destruction. To evaluate early marrow and soft tissue involvement, MRI is the modality of choice [5]. There are no pathognomonic radiological features to confirm the diagnosis on imaging alone and detection of mycobacterium tuberculosis from a bone biopsy is required. In conclusion, tuberculosis should be considered as one of the differential diagnoses for children presenting with longstanding finger swelling and pain. High index of suspicion is crucial, especially in countries like India, where Tuberculosis is endemic.