Recurrence of Hypertrophic Abductor Digiti Minimi Muscle of the Foot After Subtotal Resection

Soft tissue tumors of the foot are rare, and the diagnosis is often difficult. Surgery is indicated if pain, discomfort, or functional impairment is present or to rule out malignancy. We present the case of a 14-year-old female with a painless swelling at the lateral aspect of her right foot. After radiologic imaging, including ultrasonography and magnetic resonance imaging (MRI), we performed a subtotal resection of the abductor digiti minimi muscle, preserving its motor nerve. Four months later, recurrence of the soft tissue mass was observed. MRI revealed hypertrophy of the small muscles of the foot, including the abductor digiti minimi, quadratus plantae, and flexor digiti minimi brevis. Functional impairment resulted in complete excision of the remnant abductor digiti minimi muscle and partial excision of the flexor digiti minimi brevis muscle another 7 months later. Twelve months after the secondary surgery, neither clinical nor radiologic signs of a second recurrence were found. At the last follow-up visit, the patient was satisfied with the contour of her foot and not hindered at all during sporting activities. Our findings demonstrate that subtotal resection of a bulky muscle, preserving its motor nerve, can result in reactive hypertrophy of the remnant muscle part. The patient must be informed that partial excision of an innervated muscle could result in reactive hypertrophy and must be contrasted with radical muscle excision that might be more likely to result in functional impairment.