= NORA LESION

= benign exophytic surface lesion of bone

• Cause: ? reactive mass of heterotopic mineralization arising from periosteum of intact cortex without involvement of medullary canal
• Location: small tubular bones of hands + feet; proximal and middle phalanges (92%); metacarpal bones (8%)
• Site: diaphyses + metaphyses of phalanges

• painless progressive swelling of digit
• ± limited motion in proximity to a joint

• well-marginated ossified broad-based lesion arising from bone cortex, usually without cortical erosion
• cortical + medullary discontinuity from underlying host bone
• periosteal reaction usually absent

MR:

• uniformly enhancing T1-hypointense mass
• mass of hyperintensity on T2WI

Rx: surgical excision with wide margins in symptomatic patient

Prognosis: 55% recurrence rate within 2 years of excision

DDx: osteochondroma (cortical + medullary continuity between host bone and mass)