Apocrine Hydroadenoma Mimicking Morton’s Neuroma: A Rare Differential Diagnosis on Ultrasound

A 62-year-old woman presented with neuropathic pain and paresthesia in her right forefoot, where a circumscribed soft tissue swelling was detected between the second and third metatarsal heads on the sole. Initial ultrasound (US) imaging revealed a well-defined lesion in the second intermetatarsal space without vascularization on Power Doppler (PD), suggesting an initial diagnosis of Morton’s neuroma. However, further assessment using Magnetic Resonance Imaging (MRI) showed a dumbbell-shaped lesion situated between the second and third metatarsal heads, extending into the subcutaneous fat of the dorsal slope. These MRI findings did not align with the typical characteristics of Morton’s neuroma and suggested an atypical mass, prompting further investigation. The patient subsequently underwent a sub-total excisional biopsy, and histopathological examination identified the lesion as an apocrine hydroadenoma, an uncommon benign tumor originating from ectopic sweat glands. This is an exceptionally rare presentation, with no prior reports of apocrine hydroadenoma mimicking Morton’s neuroma in the literature. The clinical and radiological presentation of this case underscores the importance of considering rare differential diagnoses when diagnosing intermetatarsal lesions, particularly when imaging findings deviate from the classic features of common conditions like Morton’s neuroma. This case highlights the potential for apocrine hydroadenomas to mimic more common lesions on ultrasound and MRI, thus emphasizing the role of biopsy in confirming atypical diagnoses. Recognizing such rare differential diagnoses is essential for appropriate management and treatment planning, particularly in patients with neuropathic symptoms where routine diagnoses are insufficient.