The patient presented with a 3-month history of a slowly growing mass in the left thigh. Clinical evaluation revealed a non-tender palpable mass. The past medical history was clear and laboratory tests were normal.
The patient presented with a 3-month history of a slowly growing mass in the left thigh. Clinical evaluation revealed a non-tender palpable mass. The past medical history was clear and laboratory tests were normal.
On MRI, an inhomogeneous intermediate signal intensity mass was seen on T1-weighted images. This was 6.5 x 5cm in size and involved the sciatic nerve. Axial and coronal post-contrast T1-weighted images revealed peripheral enhancement of the tumour, while its central necrotic section remained unenhanced after IV gadolinium administration. The entering and exiting nerve was thickened (Fig. 1).
Surgery revealed a fusiform mass easily removed from the adjacent tissues. Pathological examination showed a malignant nerve sheath tumour with areas of necrosis (Fig. 2).
Malignant peripheral nerve sheath tumour (malignant PNST) is a spindle cell sarcoma arising from nerve. Malignant PNSTs have also been referred to as malignant schwannomas, neurogenic sarcomas, malignant neurilemmomas, and neurofibrosarcomas. They most frequently affect patients who are 20-50 years old and represent 5-10% of tissue sarcomas. A high proportion of malignant peripheral nerve sheath tumours occur in association with Type 1 neurofibromatosis. Malignant PNST generally involves the major nerve trunks including the sciatic nerve, brachial plexus and sacral plexus. Patients with malignant PNST present more frequently with pain and neurological symptoms of motor weakness and sensory deficits than do patients with benign PNSTs. Secondary malignant peripheral nerve sheath tumours arise from prior radiation treatment, with a latency period of over 10 years.
Malignant PNSTs are fusiform, due to the entering and exiting nerve, which is clearly evident on gross pathological examination. The tumour frequently spreads along the entering and exiting nerve, with the epineurium and perineurium becoming thickened proximal and distal to the mass.
The tumour cells are arranged in fascicles, resembling fibrosarcoma, and areas of haemorrhage and necrosis are frequent. Most malignant PNSTs are considered high-grade sarcomas.
The most important imaging feature that should always suggest the diagnosis of neurogenic neoplasm is recognition of a fusiform mass, which represent the tubular entering and exiting nerve in a typical nerve distribution. This relationship is usually easy to detect in lesions affecting large deep nerves. These are frequently imaged because of a clinical presentation of a nonspecific soft-tissue mass.
Because of its large field of view and multiplanar capabilities, MR imaging is superior to other imaging modalities for demonstrating the virtually pathognomonic fusiform appearance of PNST.
Although malignant and benign lesions cannot be reliably distinguished by imaging criteria, certain findings should raise the suspicion of a malignant tumour. Malignant PNSTs tend to be larger (>5cm). They may exhibit ill-defined margins suggesting infiltration of the adjacent tissues and associated oedema. Heterogeneity with central necrosis on cross-sectional imaging is common in malignant lesions, although it can be encountered in benign lesions too. Similarly, calcification, which is more commonly associated with malignant lesions, can also be present in ancient schwannomas.
Treatment of malignant PNSTs is complete surgical excision with wide resection margins. Adjuvant chemotherapy and radiation therapy are also often used. Despite this aggressive treatment, local recurrence and distant metastases are common. Metastases most frequently affect the lungs, bones, pleura and retroperitoneum.
Malignant peripheral nerve sheath tumour involving the sciatic nerve
According to the provided MR imaging, a spindle-shaped lesion is observed within the soft tissue of the left thigh, presenting as a prominent soft tissue mass. On axial views, the mass shows relatively well-defined borders from the surrounding muscle groups, though the local margins appear slightly irregular. In the longitudinal sequences, the lesion is closely associated with the surrounding nerve bundles and exhibits a characteristic “enter and exit nerve” sign. On T1-weighted images, the lesion predominantly appears slightly hypointense or isointense, while on T2-weighted or fat-suppressed sequences, it demonstrates markedly high signal. A certain degree of signal heterogeneity is noted in the central region, suggesting possible necrosis or cystic change. The lesion measures more than 5 cm in diameter. No obvious bone destruction or bone marrow involvement is observed, but edema-like changes can be seen in the surrounding soft tissues.
Considering the patient’s age (29 years), history (a progressively enlarging left thigh mass over 3 months), clinical presentation (firm consistency, no significant pain but possible local compression symptoms), imaging characteristics (a spindle-shaped mass closely related to the nerve trunk, size ≥5 cm, heterogeneous internal signals), and pathological findings highly indicative of a malignant peripheral nerve sheath tumor, Malignant Peripheral Nerve Sheath Tumor (MPNST) is regarded as the most likely final diagnosis. If uncertainty remains, further confirmation can be obtained through immunohistochemistry (e.g., S-100, SOX10 markers) or genetic testing.
Treatment Strategy:
Rehabilitation / Exercise Prescription:
This report is based on existing imaging and clinical data only and is provided for reference purposes. It does not replace a professional physician’s face-to-face diagnosis and treatment plan. Should you have any questions or if your condition changes, please contact a specialist or seek hospital care promptly.
Malignant peripheral nerve sheath tumour involving the sciatic nerve
