= DUPUYTREN EXOSTOSIS

= uncommon solitary benign bone lesion arising from distal phalanx beneath the nail producing a bony stalk under a fibrocartilaginous cap

Cause: repetitive trauma (14–25%); ? infection

Age: 2^nd–3^rd decade (range, 7–58 years); M÷F = 1÷2

Histo: inflammatory growth of proliferating fibroblasts and cartilage undergoing enchondral ossification at the base

Location: toes (86–90%, big toe in 77–80%), thumb + index finger (10–14%, dominant hand in 75%)

Site: dorsal / dorsomedial aspect of distal phalanx under / adjacent to nail bed

• rapidly growing mass ± pain + overlying skin ulceration
• radiographic appearance similar to osteochondroma:
  • broad sessile / narrow pedunculated base of bone spur
  • indistinct / well-demarcated cartilage cap larger than base
  • NO continuity to cortex / medulla of host bone (DDx to osteochondroma)
• ossific mass with trabecular bony overgrowth distal to physeal scar: ± defined cortex

US:

• heterogeneously hyperechoic lesion
• well-defined margins + calcifications
• hypoechoic fibrocartilaginous cap of <20 mm in diameter
• NO / mild vascularity

MR:

• subungual exostosis hypointense on all sequences

Rx: complete surgical excision

Prognosis: 11–53% recurrence rate

DDx: osteochondroma (exostosis continuous with cortex and medulla of host bone, hyaline cartilage of high SI on T2WI)