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Abstract
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BACKGROUND A pure intramuscular paraspinal schwannoma is an extremely rare condition, with only few case reports in the literature. Due to low frequency and lack of specific clinical signs and symptoms, pre-surgical diagnosis is difficult. Only at the pathological analysis the lesion is usually clearly identified. We report here a case in which pre-surgical imaging was highly suggestive for a diagnosis of paraspinal Schwannoma.
CASE PRESENTATION A 69-year-old female patient present unspecific right paravertebral numbness, associated with a swelling homogeneous subcutaneous mass, right-sided, without skin reaction. No neurological signs or pain were assessed. At levels D3-D5, the MRI showed a 5x2x1 cm right-sided intramuscular paravertebral isolated mass, with circumscribed margins and heterogeneous component, partly cystic. No surrounding edema was found. At the upper pole of the lesion, it was possible to identify a paraspinal nerve coming down from D1, from which the mass arises. According to clinical and radiological findings, first hypothesis was a paraspinal schwannoma arising from a right dorsal ramus of D1. An elective surgery was performed. Histopathology confirmed a rare OMS I "ancient schwannoma". The lesion was encapsulated inside a perineural sheet, with no residual tumor at the upper and lower extremity, confirming a complete resection. A clinical and radiological follow up was performed at 6 weeks postop, 6 and 12 months, with no evidence of tumor recurrence.
DISCUSSION As underlined, a paraspinal intramuscular schwannoma is very rare, especially because rarely symptomatic. Besides, it is often impossible to give a clear pre-operative suspicion of these lesion, which are usually misdiagnosed in favor of more common back masses like lipomas or hemangiomas. It is mandatory to check specifically, at MRI and intraoperatively, for an eventual hypertrophied nerve ramus from which the schwannoma could arise, in order to perform a complete resection: although benign on 99% of cases, schwannomas present 1% of malignant degeneration into neurofibrosarcoma.
CONCLUSION A schwannoma, although rare, should always be considered in the differential diagnosis when a patient with paraspinal mass lesion comes at our attention and a specific investigation with contrast enhanced-MRI is required before surgery. A complete "en bloc" resection with nerve identification is recommended, according to the rare but still possible malignant degeneration of a schwannoma.
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