Missed for Years, Cured in Hours: Surgical Excision of a Popliteal Schwannoma With Intraoperative Neuromonitoring

Popliteal schwannomas are rare benign tumors arising from the peripheral nerve sheaths, often misdiagnosed due to their nonspecific symptoms. We report a case of a 36-year-old female with a 10-year history of refractory left leg pain localized to the S1 dermatome, characterized by persistent burning and aching sensations along the plantar foot, heel, and posterior calf. Despite multiple consultations with various specialists over the years, her symptoms were repeatedly misattributed to lumbar spine pathology, resulting in delayed diagnosis. A detailed clinical evaluation eventually revealed a palpable mass in the popliteal fossa. MRI imaging showed a well-defined lesion consistent with a nerve sheath tumor arising from the tibial nerve. Histopathological examination after surgical excision confirmed the diagnosis of a tibial nerve schwannoma. Intraoperative neuromonitoring (IONM) was utilized to aid in the precise identification and preservation of nerve function during tumor excision. Neuromonitoring showed improved neural function with increased SSEP amplitude (e.g., from 0.41 µV to 0.72 µV) and decreased latency (e.g., from 47.9 ms to 43.4 ms) postoperatively in multiple channels, indicating enhanced nerve conduction. Additionally, transcranial motor evoked potentials (TcMEPs) were preserved after tumor excision, further supporting the functional integrity of motor pathways during surgery. The patient experienced complete symptomatic relief postoperatively, with no neurological deficits. This case underscores the importance of maintaining clinical suspicion for sinister pathology in patients presenting with long-standing, refractory leg pain and highlights the value of thorough clinical examination combined with appropriate imaging for the diagnosis and the importance of neuromonitoring during surgery.