Intracranial melanotic schwannomas: a rare variant with unusual adherent features

The "Pigmented Side" of Nerve Sheaths: Malignant Melanotic Nerve Sheath Tumor

Malignant melanotic nerve sheath tumor (MMNST) represents a highly aggressive neoplasm arising both in peripheral and cranial nerves. It accounts for < 1% of all nerve sheath tumors, but the real incidence may not be well defined yet because of the evolution of its nomenclature. To date, it is considered a distinct tumor type, no longer as the pigmented variant of schwannoma, with a different clinical course and biological behavior. MMNSTs exhibit a specific genetic hallmark related to the PRKAR1A gene, which explains the major incidence in Carney Complex-affected patients. One of the more frequent localizations is the paravertebral region, where it poses diagnostic concerns with both primary tumors arising from soft tissues and the meningeal covering, as well as metastatic ones (ie, melanoma). Herein we present a patient with an MMNST accompanied by the main clinical, radiological, histopathological, and molecular findings, stressing the need for a multidisciplinary diagnostic approach. To the best of our knowledge, this is the first report of proton beam therapy for MMNST. We also performed a literature review to collect and compare the more recent data in English literature and to highlight the "keep-in-mind" concepts to apply in a multidisciplinary diagnostic algorithm, with a focus on histopathology and related pitfalls.

Retroperitoneal Recurrence of Melanotic Schwannoma on 18F-FDG PET/CT

ABSTRACT

Melanotic schwannoma is an uncommon nerve sheath neoplasm. Only 10% of melanotic schwannoma are malignant whereas metastases from melanotic schwannoma are much less common. Hereby we present FDG PET/CT findings of recurrent left retroperitoneal melanotic schwannoma with widespread metastases in a 50-year-old man.

Hemorrhagic spinal melanotic schwannoma presenting as acute chest pain: A case report and literature review

Background:

Melanotic schwannoma (MS) is a rare variant of peripheral nerve sheath tumor. MS commonly arises along the spinal nerve sheath. Patients most often experience pain along the dermatome of the affected nerve root. Symptoms development is usually insidious. About half of MS cases are associated with Carney complex, a multi-neoplastic disorder. The remaining cases arise spontaneously. About 10–44% of these tumors undergo malignant transformation.

Case Description:

We describe a case of hemorrhagic MS presenting as acute chest pain mimicking myocardial infarction, a presentation which has not yet been described in the literature. Neurologic examination did not reveal any abnormalities. Myocardial infarction was ruled out in the ER, and a chest CT angiogram was ordered for evaluation of PE or aortic dissection which revealed an intradural extramedullary dumbbell-shaped mass extending through the left vertebral foramen at the level of T8. MRI revealed a heterogenous mass that was hyperintense with T2 and hypointense with T1-weighted imaging. The patient underwent an open laminectomy of the left T8 and T9 vertebrae and gross total resection (GTR) of a hemorrhagic black tumor. Microscopic examination showed fascicles and nests of plump spindle cells with variable intracellular melanin. Immunohistochemistry showed the cells to be positive for S100, SOX10, HMB-45, and MART-1, confirming diagnosis of MS. Two months after the operation, the patient was doing well and is free of recurrence.

Conclusion:

GTR is considered the optimal treatment for MS; radiotherapy and chemotherapy may be considered but have not been shown to improve patient outcomes.

Brain and spine melanotic schwannoma: A rare occurrence and diagnostic dilemma

PURPOSE

Melanotic schwannoma (MS) was formerly known as a rare variant of schwannoma. The behavior of MS is unpredictable, with a tendency for recurrence and metastasis. The purpose of this study was to illustrate the imaging characteristics of these rare and misdiagnosed tumors. The prognosis of MS is discussed, along with the importance of follow-up exams to assess for recurrence and metastasis. Furthermore, we compare our results with those previously published on MS in order to have a better understanding of this rare entity.

METHODS

Three MS cases were encountered between 2008 and 2015 at our institute. All available data were reviewed, including the clinical history, imaging findings, operative notes, and the histopathology results. A follow-up magnetic resonance imaging (MRI) scan was also reviewed up to 23 months post surgery to assess for recurrence.

RESULTS

Three cases of MS are included: one in the brain and two in the spine. The brain lesion was in the occipital region. The spine lesions were thoracic intramedullary and sacral intradural. All cases were hypointense on T2-weighted imaging. Gross total resection was achieved for all lesions without adjuvant therapy. To date, the brain lesion recurred 15 months after surgery.

CONCLUSIONS

MS is a rare and distinct entity rather than a variant of schwannoma, and it poses both diagnostic and management dilemmas. Although MS has characteristic MRI features, including T1 and T2 shortening, the preoperative diagnosis is always challenging. Accurate diagnosis is crucial for management planning, including long-term follow-up exams to assess for recurrence and metastasis.

Giant Melanotic Malignant Peripheral Nerve Sheath Tumor in the Pelvis: Contrast-Enhanced CT and 18F-FDG PET/CT Finding

Melanotic malignant peripheral nerve sheath tumor is an extremely rare tumor, which originates from the neural crest, and more than half the cases are associated with Carney complex (myxomas, spotty pigmentation, and endocrine abnormalities). Herein, we have presented a case of a melanotic malignant peripheral nerve sheath tumor, which is not associated with Carney complex. The patient underwent preoperative nonenhanced CT, contrast-enhanced CT, and F-FDG PET/CT scans, which showed a large pelvic tumor with heterogeneous enhancement and increased F-FDG uptake. Subsequently, the patient underwent complete resection of the tumor.