INTRAMEDULLARY THORACIC MENINGIOMA: A RARE CASE REPORT AND REVIEW OF THE LIT- ERATURE

Only a few cases of intramedullary meningiomas in the cervical and thoracic region have been reported in the literature. We present a rare case of intramedullary meningioma in the lower thoracic region. A 68-year-old woman with complaints of back pain, gait disturbance, and paresthesias in both lower extremities for 4 months was admitted to our institution. Initially, she presented with weakness in her legs that gradually deteriorated over time. The patient had been operated on for breast cancer 2 years prior to the onset of current complaints. The neurological examination revealed spastic inferior paraparesis (McCormick grade IV), hypoesthesia below Th10 dermatome, bowel and bladder disturbances. Magnetic resonance imaging of the thoracic spine demonstrated intramedullary tumor that was hypointense on T1 and T2-weighted images but showed homogenous enhancement after gadolinium administration. After gross total resection, the histopathological examination confirmed the diagnosis of atypical intramedullary meningioma. CONCLUSION: The intramedullary meningiomas are extremely rare, but they should not be excluded from the differential diagnosis, especially in cases of intramedullary tumors with homogenous enhancement on magnetic resonance imaging. The best treatment strategy is gross total removal of the tumor.


INTRODUCTION
Spinal meningiomas can occur in each segment of the spine, but they are most common in the thoracic region. Intradural extramedullary meningiomas account for 25% to 50% of all intradural extramedullary tumors, and the incidence is 0,5-2/100 000 per year [1]. Intra-extradural spinal meningiomas represent 5% -6% of the cases [2]. Only a few cases of intramedullary meningiomas have been reported in the literature [3].
We present a rare case of intramedullary meningioma in the lower thoracic spine and put stress on its clinical presentation, imaging findings, surgical techniques, and pathological results.

CASE REPORT
A 68-year-old woman had been operated on for breast cancer 2 before her current admission. She presented with progressive complaints of back pain, impaired gait, and paresthesias in both lower extremities. Gradually, she became dependent and was not able to walk unassisted. The neurological examination revealed spastic inferior paraparesis (McCormick grade IV), conductive hypoesthesia below Th10 dermatome, positive Babinski sign bilaterally, bowel and bladder disturbances. The thoracic magnetic resonance imaging (MRI) demonstrated an intramedullary lesion, measuring 9.1mm in the sagittal plane at the level of T12 vertebra that was hypointense on T1 and T2-weighted images (Fig. 1). After gadolinium administration, the mass showed homogeneous enhancement (Fig. 2).  Taking into account the history of oncological disease, the lesion was initially interpreted as intramedullary metastasis. The patient underwent a T11 -T12 laminectomy, midline durotomy and ultrasonic localization of the lesion. After posterior midline myelotomy, a pale grayish tumor was visualized that had rubbery consistency ( Fig. 3 A). Using microsurgical technique, gross total resection of the tumor was achieved (Fig. 3 B). The histopathological examination confirmed a tumor with a presence of small, atypical, hyperchrome cells expressing high mitotic index, macronucleoli, and hypercellularity. The diagnosis of atypical meningioma (Grade II WHO) was confirmed (Fig. 4).
In the postoperative period, the patient demonstrated favorable recovery of the neurological deficit. At the second postoperative week, she was able to walk assisted. At the 8th postop month, she died due to progression of the systemic breast cancer disease.

DISCUSSION
Intradural extramedullary meningiomas account for 25% -46% of the spinal tumors [3]. The peak incidence of spinal meningiomas is between the 5th and the 7th decade, but they can occur at any age. Women are commonly affected (75-80% of the cases), and the female: male ratio is 4:1-8:1 [2].
Spinal meningiomas demonstrate homogenous enhancement after gadolinium administration and appear mildly hyperintense on T1-and T2-weighted MRI images [4]. Another typical characteristic is the so-called "dural tail sign" observed on post-contrast T1 MRI series but in the case of intradural extramedullary localization [3].
Because of their rarity, the imaging characteristics of intramedullary meningiomas are not well described. In most cases, they are iso-or hypointense on T1 sequences and mildly hyperintense on T2 sequences (with homogeneous enhancement?) [7]. This is also confirmed in our clinical case. The pathogenetic mechanism of development is still unknown. According to Moriuchi et al., meningocytes are modified fibroblasts deriving from mesenchymal cells. Therefore, intramedullary meningiomas could develop in the mesenchymal cells lining the perivascular spaces of the neuraxis [8].
Surgery should be the primary treatment. Total tumor resection is usually possible using a meticulous microsurgical technique. Interestingly, satisfactory results are reported after gross total or partial resections [3,8,10,11,18,19].
The histological types of reported intramedullary meningiomas are presented in Table 1. We can summarize that most of them are not benign, consistent with WHO Grade II, a fact also confirmed by our case. Therefore, cautious MRI follow-up is needed to detect early signs of recurrence. In such cases, adjuvant radiotherapy should also be considered.