The Sarcoma Masquerader: Vascular Leiomyoma of the Popliteal Fossa Encasing the Common Peroneal Nerve

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Vascular leiomyoma, also known as angioleiomyoma, is a rare benign soft-tissue tumour arising from vascular smooth muscle. Deep-seated lesions in the popliteal fossa with major peripheral nerve involvement may create substantial diagnostic and surgical challenges. A 48-year-old woman presented with a 6-month history of a progressively enlarging, painful mass in the left popliteal region, without an initial distal neurovascular deficit. Ultrasonography (USG) demonstrated a vascular heterogeneous hypoechoic lesion, while magnetic resonance imaging (MRI) showed a lobulated enhancing mass intimately related to the common fibular (peroneal) nerve and adjacent vessels, with diffusion restriction raising concern for sarcoma or a malignant peripheral nerve sheath tumour. Fine-needle aspiration cytology (FNAC) and subsequent core needle biopsy suggested a benign soft-tissue or spindle cell tumour, creating radiological-pathological discordance. At surgery, the mass completely encased the common peroneal nerve and could not be separated without compromising the intended surgical margin. Wide local excision with en bloc resection of the involved nerve segment was therefore performed. Histopathological examination demonstrated a well-circumscribed spindle cell neoplasm arranged in intersecting fascicles with thick-walled vascular channels and no significant atypia, mitotic activity, or necrosis, supporting a diagnosis of vascular leiomyoma. Postoperatively, the patient required an ankle-foot orthosis (AFO) and rehabilitation for the expected neurological deficit. At 6 months, she remained disease-free with improved mobility.