Palpable soft-tissue mass on the posterior aspect of the right thigh
An otherwise healty 38-year-old female patient presented with a slowly growing mass in the posterior aspect of her right thigh. Clinical examination revealed a mobile, moderately tender mass. Tinel’s sign (paraesthesias produced by percussing the tumour) was negative. Radiographs were normal. MRI scan was performed. An ovoid mass oriented longitudinally in the common peroneal nerve distribution was demonstrated. The lesion was iso-slightly hyperintense relative to muscle on T1-weighted images (Fig 1 a,b) and predominantly of high signal intensity with low-signal-intensity central cystic degeneration area on T2-weighted images (Fig 2 a,b). After IV administration of gadolinium chelates the mass was diffusely enhanced except for central cystic degeneration area (Fig 3 a,b). Surgical resection followed with histopathological examination allowed the diagnosis of an ancient schwannoma.
Schwannomas and neurofibromas are the most commonly seen benign peripheral nerve sheath tumors that arises from the schwann cells of the nerve sheath [1-3]. Malignant peripheral nerve sheath tumors could also be seen and both benign and malignant forms can be associated with neurofibromatosis [1]. Most of schwannomas present as a slowly growing, painless soft-tissue mass [1]. They are usually solitary, encapsulated and mobile in palpation. Schwannomas occur in the 2nd to 5th decade of life with no sex predilection [2,3]. Degeneration and cystic cavitation are much more common in schwannomas than in neurofibromas [1]. “Ancient” schwannomas refer to long-standing degenerative lesions with calcification, hyalinization, and cystic cavitation [1]. These degenerative changes can be misdiagnosed as malignant fibrous histiocytoma, malignant peripheral nerve sheath tumor, liposarcoma, synovial sarcoma or hemangiopericytoma [3]. The malignant degeneration of a schwannoma is extremely rare.
Sonography shows a well-defined, homogeneous, hypoechoic ovoid mass with a healthy nerve at the proximal and distal aspects of the mass [2,3]. CT reveals a low density well-circumscribed, inhomogeneous mass. MRI is the best imaging modality for evaluating schwannomas. The “target sign” has been reported for 52% of benign nerve sheath tumors which is composed of a peripherally hyperintense rim and a central low intensity area on T2-weighted images [3]. Although the target sign is seen more frequently in neurofibromas, it may be seen in schwannomas as well [4]. The “split-fat sign” represents a rim of fat surrounding the margins of the nerve sheath tumor in an intermuscular location. MRI also shows associated muscle atrophy and the relationship with the nerve [1]. They are isointense or slightly hyperintense relative to muscle on T1- weighted images and markedly hyperintense on T2-weighted images. Ordinary schwannomas show strong enhancement by gadolinium contrast [3]. Hence schwannomas are generally separable from the underlying nerve fibers, surgical excision can usually spare the parent nerve [1].
Schwannoma of the common peroneal nerve
Based on the MRI images, an oval-shaped soft tissue mass with clear boundaries and an intact capsule is observed in the posterior region of the right thigh. On T1-weighted images, its signal is roughly isointense or slightly hyperintense relative to muscle, and on T2-weighted images, it appears hyperintense. Part of the lesion demonstrates a “target sign” characterized by peripheral high signal and a relatively low signal center, and there is a fat rim around the tumor known as the “split-fat sign.” No significant infiltrative destruction is observed in the surrounding structures; adjacent muscles appear normal in shape, and no bone destruction signs are present. Imaging indicates that the tumor is closely associated with the nearby nerve bundle but appears to be separable from it.
Considering the patient’s age (38 years), clinical presentation (a palpable soft tissue mass in the posterior right thigh, slow growth, minimal pain), and imaging features, the following possibilities are suggested:
Taking into account the absence of significant pain, lack of neurological deficits, slow growth of the lesion, appearance of the “target sign,” and an intact capsule, the most likely diagnosis is a peripheral nerve sheath tumor (schwannoma). Definitive confirmation requires surgical excision with subsequent pathological and immunohistochemical evaluation to rule out rare malignant transformation or other types of soft tissue tumors.
1. Treatment Strategy:
For confirmed benign schwannomas, if the tumor is large or causes local pain or nerve compression symptoms, surgical removal is the first choice. During surgery, the mass can often be separated from the nerve to minimize damage to normal nerve fibers. If the tumor is small, causes few symptoms, and shows no progressive enlargement or neurological deficits, regular follow-up may suffice.
2. Rehabilitation and Exercise Prescription:
After surgical treatment, gradual rehabilitation exercises should begin once the incision has healed and upon approval by the attending physician. Based on the FITT-VP principle, the following plan is recommended:
During rehabilitation, monitor for neurological symptoms in the affected leg (numbness, pain, tingling), changes in muscle strength, and joint mobility. Adjust the exercise plan as needed. If the patient has other chronic conditions or lower cardiopulmonary fitness, individualized rehabilitation under professional supervision is essential to ensure safety.
Disclaimer:
This report is based on current imaging and clinical information and is provided as a reference. It does not replace in-person consultation or professional medical advice. The final diagnosis and treatment plan should be determined by a specialist based on the patient’s overall clinical scenario.
Schwannoma of the common peroneal nerve
