# Low-Grade Malignant Peripheral Nerve Sheath Tumor: A Case Report of Exceptional Parapatellar Location in the Knee

## TL;DR

This case report describes a rare low-grade peripheral nerve sheath tumor located in the knee of a 46-year-old woman.

## Contribution

The novelty lies in the exceptional parapatellar location of the tumor, which is uncommon for such malignancies.

## Key findings

- The tumor was diagnosed as low-grade through histopathological and immunohistochemical analysis.
- The patient underwent resection and radiotherapy with no local recurrence after one year.
- Radiological imaging showed a heterogeneous soft tissue mass without hemorrhagic components.

## Abstract

Malignant tumors of the peripheral nerve sheaths are uncommon, constituting a small percentage, typically ranging from 2% to 5% of soft tissue sarcomas. Etiological diagnosis is often difficult but is guided by imaging and confirmed by histopathological and immunohistochemical examination. We report a case of a 46-year-old woman admitted for management of a mass in the medial parapatellar region of the right knee. Her medical history included a burn to the right leg five years ago and a previously undocumented resection of a medial parapatellar tissue mass in the right knee. Radiological examination showed a deep and superficial soft tissue mass in the medial soft tissue of the right knee opposite the patella, with no hemorrhagic components and heterogeneous enhancement after injection of gadolinium. Histopathology confirmed the diagnosis of a low-grade peripheral nerve sheath tumor, and a thoracic-abdominal-pelvic CT scan was performed, which was normal. Treatment consisted of a simple carcinological resection and local radiotherapy. No local recurrence was noted after one year of follow-up.