Subcutaneous phaeohyphomycosis: ultrasound findings and histopathologic correlation.

Abstract

Subcutaneous phaeohyphomycosis is a rare opportunistic fungal infection caused by dematiaceous fungi and may clinically and radiologically mimic benign cystic or inflammatory soft tissue lesions. Imaging descriptions of this entity remain scarce. We report the case of a 60-year-old woman who presented with a slowly growing subcutaneous nodule. Ultrasound examination demonstrated a well-circumscribed hypoechoic pseudocystic lesion containing heterogeneous internal echoes and peripheral hypervascularity. Based on the imaging findings, the initial differential diagnosis included an epidermoid cyst and an inflammatory collection. Surgical excision followed by histopathological analysis revealed granulomatous inflammation containing pigmented septate fungal hyphae associated with a retained plant fragment (thorn), confirming the diagnosis of subcutaneous phaeohyphomycosis. Although the ultrasound appearance was not specific, it provided valuable characterization of lesion morphology, internal content, and vascularity, facilitating diagnostic assessment and guiding further management. This case is noteworthy because it illustrates the sonographic-pathologic correlation of a rare fungal infection associated with a retained vegetal foreign body and highlights imaging features that may increase awareness of this uncommon entity among radiologists, helping to reduce diagnostic delay and improve recognition of superficial fungal infections.