Apposed ("Kissing") Diaphyseal Osteochondromas of Adjacent Metatarsals in a Non-syndromic Adult: A Case Report.

Osteochondroma is the most common benign bone tumour but characteristically arises from the metaphysis of long bones during the first two decades of life and ceases growing at skeletal maturity. Metatarsal involvement, new symptomatic onset in adulthood, and a diaphyseal origin are each individually uncommon. We report a 47-year-old woman who presented with four months of progressive, atraumatic dorsal pain and swelling of the left foot and a fixed, tender bony mass in the first intermetatarsal space. Radiographs showed two apposed ("kissing") sessile outgrowths arising from the lateral cortex of the first and the medial cortex of the second metatarsal diaphyses, each maintaining corticomedullary continuity with the parent bone. Magnetic resonance imaging (MRI) showed no discernible cartilage cap, with incidental cuboid marrow oedema and a minimal tibiotalar effusion; inflammatory and metabolic markers were normal. Because of the atypical adult onset, symptomatic progression and clinical-imaging discordance, en bloc excision was performed. Histopathology confirmed a benign osteochondroma with a 1-mm hyaline cartilage cap overlying mature lamellar bone, without atypia. Symptoms resolved completely by three months, with no radiographic recurrence. Apposed diaphyseal osteochondromas on adjacent metatarsals can occur in a non-syndromic adult, departing from the classical metaphyseal, skeletally immature paradigm. A thin cartilage cap may be undetectable on MRI, so histological confirmation is essential when imaging and clinical suspicion diverge; complete excision is curative.