A 48-year-old man underwent an MRI examination for investigation of a soft-tissue mass arising from the medial aspect of his left hind-foot.
A 48-year-old man presented with a several-month history of a slowly enlarging lump on the medial aspect of his left heel. Examination revealed a large, firm superficial mass which was slightly tender to palpation. The overlying skin appeared normal. An MRI was performed. T1 weighted imaging demonstrated a lobulated, intermediate signal intensity soft tissue mass, measuring 6.5cm in maximum diameter, medial to the left calcaneous (fig 1). The lesion had caused significant erosion of the underlying bone, however there was no evidence of oedema in the adjacent marrow. On short-tau inversion recovery (STIR) imaging, the mass demonstrated heterogenous signal intensity, being predominantly high in signal but with several areas of low signal centrally (fig 2). Avid enhancement of the lesion was shown following gadolinium administration (fig 3). A percutanous biopsy was performed. Histological analysis of this specimen showed features of a nerve sheath tumour with occasional cellular atypia and large areas of hypocellularity, in keeping with an ancient schwannoma.
Ancient schwannomas, also known as degenerative neurilemmomas, are very rare, benign tumours which show characteristic features of degeneration on histologic examination (1). While typical schwannomas demonstrate a biphasic cellular pattern consisting of highly cellular areas (Antoni A) and myxoid areas (Antoni B), ancient schwannomas have relatively little Antoni A tissue, and also show perivascular hyalinisation, cystic necrosis and calcification. In addition, nuclear atypia is often present and may be misinterpreted as malignancy (2). These lesions are most commonly found in elderly patients, and usually have been present for a long time before diagnosis (3). Occasionally, as is the case with typical peripheral schwannomas, percussion of the lesion may elicit pain in the distribution of the nerve of origin (4). On radiographs, a soft tissue mass may be evident; erosion of adjacent bone has been reported (1). While calcification is often present histologically, it is not usually visible radiographically, nor is it a common finding on CT (5). On MR imaging, these tumours are typically lobulated and are isointense to skeletal muscle on T1 weighted imaging, with heterogenous but predominantly high signal on T2 weighted imaging (3). The target appearance (peripheral high signal with a central area of lower signal on T2 weighted imaging) seen in approximately 50% of typical peripheral schwannomas is not present in ancient schwannomas (3). The heterogeneity of signal intensity corresponds to areas of necrosis, haemorrhage and cyst formation histologically. These lesions are hypervascular and therefore enhance avidly with iodinated contrast and with gadolinium. Because of the MRI appearances, these tumours are sometimes misinterpreted radiologically as malignant neoplasms, such as malignant fibrous histiocytoma, malignant peripheral nerve sheath tumour, liposarcoma or synovial sarcoma. As ancient schwannomas do not tend to recur following simple enucleation, accurate pre-operative diagnosis helps avoid unneccessarily radical surgery (5).
Ancient Schwannoma.
Based on the MRI of the medial hindfoot of the patient’s left foot, a relatively large, lobulated soft tissue mass can be observed in the medial soft tissue. The specific imaging characteristics include:
Considering the patient’s age of 48 and the imaging features, the following diagnoses or differential diagnoses can be taken into account:
Taking the patient’s age, growth characteristics of the soft tissue mass, MRI signal features (heterogeneous hyperintensity on T2, marked enhancement, and signs of degeneration), and the tumor’s location along a nerve pathway into account, the most likely diagnosis is:
Ancient Schwannoma (Degenerative Schwannoma).
If there remains any doubt, definitive confirmation requires correlation with pathological or biopsy findings. Surgical excision of the mass followed by histological examination can usually confirm the diagnosis.
Treatment Strategies:
Rehabilitation/Exercise Prescription Recommendations:
Disclaimer: The above analysis report is for reference only and cannot replace in-person diagnosis or professional medical advice. If you have any concerns, please consult an orthopedic or relevant specialist for a more comprehensive and personalized treatment plan.
Ancient Schwannoma.
