Background
Perineural spread in rectal cancer is a rare occurrence, particularly when it extensively disseminates along the lumbosacral plexus, as well as the sciatic and pudendal nerves. Its diagnosis is challenging and represents a critical prognostic factor owing to its association with higher recurrence and metastasis rates.
Case presentation
A 55-year-old Spanish female with a history of rectal adenocarcinoma underwent standard treatment, including neoadjuvant chemoradiotherapy, ultra-low anterior resection, and adjuvant chemotherapy. Five years later, a fluorine-18 fluorodeoxyglucose positron emission tomography-computed tomography scan detected a hypermetabolic lesion near the right piriformis muscle and internal iliac vessels, leading to surgical excision and radiotherapy, which confirmed metastasis. Three years after that, the patient presented with right-sided sciatica. Magnetic resonance neurography revealed characteristic features of perineural spread, including thickening, hyperintensity, enhancement, and diffusion restriction of the right sciatic and pudendal nerves, as well as the sacral roots (S1–S4). These findings differed from other neuropathic conditions, such as tumoral compression, traumatic neuropathy, and post-radiotherapy changes. Positron emission tomography-computed tomography and biopsy confirmed adenocarcinoma. Despite additional chemotherapy, the disease progressed, resulting in cerebral, lung, and bone metastases. The patient passed away 1 year later.
Conclusion
This case highlights the potential role of the magnetic resonance neurography in the accurate diagnosis of perineural spread in rectal cancer, emphasizing the value of functional magnetic resonance neurography sequences in differentiating it from other causes of neuropathic pain. This is essential for clinicians, as perineural spread is associated with a poor prognosis and necessitates appropriate management.
