Intraosseous schwannomas are a group of rare benign osseous lesions that account for about 0.2% of all primary bone tumors. They are the most common benign peripheral nerves tumor arising from Schwann cells of the neural sheaths, but its intraosseous manifestation is very rare 1.
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Epidemiology
It can present at any age group although the peak age at the time of diagnosis is usually in the fourth to sixth decades of life with no predilection for gender or ethnicity 2.
Clinical presentation
Intraosseous schwannomas are a slow-growing tumor with an insidious and long period of evolution. Pain is the leading symptom in the majority of cases, associated with or without edema, but some cases may present with a pathological fracture at diagnosis 3-5.
Although intraosseous schwannomas can be found anywhere within the skeleton, mandibular involvement is the most common. Other commonly affected bones include the tibia, femur, fibula, humerus, radius, ulna, vertebrae, patella, petrous apex, scapula, and metacarpals 6.
Pathology
Schwannomas are usually composed of spindle cells with elongated nuclei and alternation of Antoni A (hypercellular) and Antoni B (hypocellular) patterns. Verocay bodies as alternating of nuclear palisades with fibrillar areas could be seen in some more typical cases as well. The existence of Antoni A regions with no evidence of nuclear palisading represents malignant neoplasms, such as synovial sarcoma or leiomyosarcoma. IHC study these tumors confirmed by strong and diffuse positivity for S-100 protein. SOX-10 and pericellular positivity to anti-collagen IV antibody also are the other markers that can be observed 7.
Radiographic features
Plain radiograph
Intraosseous schwannoma manifests as a well-circumscribed lytic bone lesion, likely with a sclerotic rim, which occasionally tapers or destroys the bone cortex. Adjacent soft tissues are rarely invaded. There is no calcification or bone tissue formation within the lesion 3-5.
MRI
Schwannoma is a solid well-marginated solid expansile lesion mostly to be isointense to skeletal muscle on T1-weighted imaging and hyperintense and/or heterogeneous on T2-weighted imaging 8. Cortical involvement may also be seen.
Treatment and prognosis
Intraosseous schwannoma has a good prognosis usually without malignant transformation. The treatment, if necessary, is curettage of the bone tumor followed by grafting 9. In one case series, an incomplete tumor excision was associated with a high recurrence rate (16%) in contrast recurrence was not detected in cases with complete surgical removal 10.
Differential diagnosis
Differentiating between the intraosseous schwannoma from the other benign bone lesions such as aneurysmal bone cyst, chondroblastomas, giant cell tumors of bone, fibrous dysplasia, and non-ossifying fibroma is difficult.
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