MELANOTIC SCHWANNOMA OF THE LUMBAR SPINE: A CASE REPORT AND LITERATURE REVIEW SCHWANNOMA MELANÓTICO DE LA COLUMNA LUMBAR: REPORTE DE UN CASO Y REVISIÓN DE LA LITERATURA

Schwannomas are benign tumors, usually solitary, encapsulated, slow-growing, which have their origin in differentiated neoplastic Schwann cells with extramedullary intradural usual development related to nerve roots. The melanotic schwannoma is a variant of these tumors whose location in almost one third of cases is on the posterior spinal nerve root, with a nonspecific clinical presentation. Magnetic resonance imaging is the most widely used test for the diagnosis, revealing hyperintense T1-weighted sequences and hypointense T2-weighted sequences. Diagnostic confirmation is obtained by histological and immunohistochemical studies, in which there is intense cytoplasmatic pigmentation. There are two distinct types of melanotic schwannomas: sporadic and psammomatous, the latter related to the called Carney complex, a form of multiple endocrine neoplasm with familiar character. In literature we found few cases of these neoplasms, the largest series consisting of five cases. The objective of this study is to report a rare case of melanotic schwannoma of the lumbar spine of the sporadic type of extramedullary location. We also present a brief review of the literature containing the main characteristics of the tumor, including its different forms, differential diagnoses, data from histological and immunohistochemical studies as well as the currently recommended approach in order to contribute to a better understanding of this neoplasm.


INTRODUCTION
Schwannomas are benign, usually solitary, encapsulated and slow growth tumors originated from differentiated neoplastic Schwann cells, representing approximately 30% of primary tumors of the spine, normally developing extramedullary and intradural related to nerve roots. 1 The melanocytic schwannoma is a variant of these neoplasms that occurs at younger ages compared to other schwannomas, being located in almost one third of cases in the posterior nerve root, 2,3 although it can also be found in soft tissue, heart, orbit, oral cavity, stomach, bronchi, retroperitoneum, cervix and parotid. 1,2It has nonspecific clinical presentation, with secondary pain and root compression and dysesthesias, besides progressive motor and sensory deficits. 2,3][4] In the literature, we found few cases of melanocytic type schwannoma in the spine, the largest series consists of five cases. 2 Thus, based on its extreme rarity, this paper aims to report a case of melanocytic schwannoma of the lumbar spine and conduce a brief literature review.

CASE REpORT
Male patient, 37 years old, without previous comorbidities, was referred to the Spinal Surgery Department of Hospital Santa Casa de Misericordia de Vitoria (HSCMV), ES, Brazil, with severe pain in the upper lumbar spine started two months before, radiating to the right anterolateral thigh, with radicular pattern in L1 and L2.
This study was approved by the Ethics Research Committee of EMESCAM with Presentation Certificate for Ethics Assessment number 19485813.0.0000.5065.
The anteroposterior radiographs of the spine showed deletion of L1 pedicle to the right.During diagnostic testing by computed tomography (CT) and MRI of the lumbar spine, a voluminous expansive injury of aggressive nature was revealed, with spontaneously hyperintense signal on T1, heterogeneously low in T2, occupying the right half of the vertebral body of L1, as well as its rear arc, breaking its lateral cortex, creeping into the neural L1-L2 right foramen, with an intracanalar component in "dumbbell" shape and showing no cleavage plane with the ipsilateral psoas.The injury measured 7.8 x 4.2 x 2.6 cm (LxTxAP) determining extension of corresponding neural foramen and compressive effect with reduced amplitude of the spinal canal.(Figure 1) A surgical posterior approach was held, with resection of the posterior vertebral elements and release of the vertebra and iliopsoas muscle bilaterally, followed by instrumentation two levels above and two below the injury site.Material collected for histopathological study revealed fusiform morphology with intense cytoplasmic pigmentation, suggestive of metastatic melanoma.The immunohistochemical examination, however, revealed cytoplasmic and nuclear expression of S100 protein, vimentin, HMB-45, Ki-67 and SP6.This lead to the conclusion, based on the findings and morphological characteristics of the injury, that it was a melanocytic non psammomatous schwannoma.(Figure 2) The patient recovered well postoperatively, returning to walk the next day.Fifteen days later the patient was re-operated, this time by anterior approach with retro peritoneal access to L1, and the tumor invading the right iliopsoas muscle was seen, encapsulating the ipsilateral genitofemoral nerve.The chosen procedure was a complete block resection of the tumor with the anterior body of L1 and the muscle in which it was infiltered, associated to anterior arthrodesis with autologous iliac graft.(Figures 3 and 4) Chest drainage and placement of a suctor drain were performed.The patient evolved in the immediate postoperative period with L2 root neuropraxia, recovering after a month with physical therapy.

DISCUSSION
Detailed results of the literature review, including gender and age of patients, location and level of injury, as well as the treatment adopted and the follow up of cases are illustrated in Tables 1 and 2. [1][2][3][4][5][6][7][8] We found a mean age of about 50 years old, the masculine gender being present in slightly more than half of the cases reviewed.The thoracic level was the most affected, with prevalence of extramedullary location (eight of the eleven reported cases), as well as in our patient, in which we found the development of extramedullary and intradural injury.Regarding treatment, partial resection was adopted in only one of the reports, in which the patient died in the immediate postoperative.In two cases there was local recurrence of the tumor after two years of follow-up, with reports of no reccurence in four cases, although the follow-up period was considered short, of slightly less than two years on average (between 10 months and 4 years).
There are two distinct types of melanocytic schwannomas: sporadic or non psammomatous and melanocytic psammomatous, the latter related 50% of the time to the so-called Carney complex. 1 It is a form of familial autosomal dominant multiple endocrine neoplasia, characterized by the presence of skin and mucosa pigment alteration, primary nodular pigmentary adrenocortical disease, cardiac and cutaneous myxomas, GH and prolactin producer pituitary adenomas, testicular cancer, adenoma or carcinoma of the thyroid, as well as ovarian cysts. 1,9Given the association of the disease with systemic manifestations, besides its hereditary nature, active investigation of patients and their families is of capital importance for the prevention of future events. 8In the reported case, the patient had no family history or even components of the Carney complex.
The main differential diagnosis of melanocytic schwannomas include malignant melanoma, meningioma and pigmented neurofibroma, rhabdomyosarcoma, clear cell sarcoma of soft tissue, melanocytic medulloblastoma, and ganglioneuroblastoma, among others. 8nitially, most patients receive a diagnosis of primary or metastatic malignant melanoma. 10Microscopically, melanocytic schwannomas are typically composed of cells with abundant intracytoplasmic melanin pigmentation, besides psammomatous bodies in cases of non sporadic injury.Immunohistochemical study reveals a coloring pattern typical of other nerve sheath tumors, strongly expressing S-100 protein, Leu-7 and vimentin, while GFAP, CK and EMA are negative.The positivity for HMB-45 and Melan-A is an unexpected finding, given that these antibodies are considered relatively specific for the diagnosis of malignant melanoma. 10eports indicate that in 10% of cases melanocytic schwannomas are malignant tumors, 1,4,7 suggesting that the presence of melanocytic Schwann cells could predispose to malignant transformation in some patients.[3][4]7 Moreover, studies have shown that among patients who were followed for more than five years, only slightly more than half were disease free at the end of follow-up, suggesting that long term monitoring is necessary to assess tumor recurrence and risk of metastasis. 10

fINAl CONSIDERATIONS
The ideal surgical approach is still complete resection of the tumor without aggravating the neurological deficits, the success of the surgery depending on the degree of malignancy and the presence of bone and visceral metastases. 8The value of radiotherapy remains unclear, 2 needing larger prospective studies with longer follow-up to better understand the natural history, prognosis and ways to approach the injury.

Figure 4 .
Figure 4. PA radiograph (left) and profile radiograph (right) of the lumbar spine showing the lumbar arthrodesis with autologous iliac graft.

Figure 1 .
Figure 1.Magnetic resonance imaging in sagittal (left) and coronal cuts (right) in T1: hyperintense injury destroying L1 vertebral body, compressing the spinal canal and infiltrating right psoas muscle.

Table 1 .
Literature review on reported cases of melanocytic schwannoma regarding year of publication, author, age and gender of patients, level and location of spinal injury*.

Table 2 .
Literature review regarding resection characteristics and recurrence of injury.