Malign peripheral Nerve Sheath Tumors (MPNST), as defined per the 2013 WHO classification, are malignant tumors arising from a peripheral nerve, or from a pre-existing benign nerve sheath tumor. They can also occur in a patient with neurofibromatosis (NF-1).
Aside from these conditions, the diagnosis is based on evidence of Schwannian differentiation as revealed by mixed histologic, phenotypic and ultrastructure features. MPNST is a very uncommon malignant type of neoplasm  . Despite their scarcity, MPNST cases were found in different regions of the body whether or not associated with neurofibromatosis type 1 (NF1)    . Cases of MPNST were mainly observed in soft tissues  , less frequently in the bones  . Isolated cases were found in the spine and femur. The authors hereby report a case of slow spinal cord compression indicative of a MPNST.
Mr. D. M., aged 29, with no specific medical prior history, was admitted with gradual onset of motor deficit in the lower limbs. Symptoms had been developing for 8 weeks, including back pain upon coughing that radiated around left side of the body to the middle of the chest, then painless intermittent claudication occurred. A week before he was admitted, he experienced motor decline in the pelvic limbs with acute urinary retention requiring consultation in the emergency department. He had neither fever nor cough, and presented no signs of trauma. His examination revealed a generally altered condition with WHO performance indicator estimated at 3/4. The neurological examination highlighted spastic paraparesia with muscle strength rated at 3/5 and a bilateral Babinski sign. Sensitivity disorders such as hypoesthesia upon protopathic touch and the rmalgesic type of disorders were found with sensitivity up to dermatome T2. He had sharp pain from T2 to T5. Skin smear examination revealed neither brown skin patches nor neurofibromas. Blood test (CBC Normal, CRP negative) and tuberculin skin test were negative. Spinal MRI (Figure 1 and Figure 2) showed a 5 cm tumor mass, low signal intensity on T1 at the level of T2 thoracic vertebra and high signal intensity on T2 with bone marrow involvement. Tumor-induced slow spinal cord compression was diagnosed and laminectomy was taken with tumor resection. The pathological examination of the resected specimen was carried out in Europe and the results were sent back 6 weeks later. Proliferation of monomorphic malignant spindle cell tumors was evidenced, with predominance of hemangiopericytoma structure (figure 3). The morphological and phenotypic profile of this tumor suggested a Malignant Peripheral Nerve Sheath Tumor (MPNST) with glandular differentiation. Extension work up specifically thoracic-abdominal-pelvic CT scan revealed no particularities. The patient passed away with respiratory distress, 1 month after he was discharged, and before getting the histological and immunohistochemical results.
Figure 1. Spinal MRI showing a vertebral body in low signal intensity on T1 at the level of T2 thoracic vertebra.
Figure 2. Spinal MRI showing high intensity on T2 at the level of T2 thoracic vertebra with bone marrow involvement.
Figure 3. proliferation of monomorphic malignant spindle cell tumors predominantly of hemangiopericytoma structure.
MPNST is a nervous system tumor which develops to the detriment of the nerve sheath, resulting from the impairment of derived neural crest and ectoderm cells  . It is a rare tumor with an incidence of 0.001% among the general population and 5% - 10% among NF1 patients  . It is much higher among NF1 patients because the NF1 gene located on the long arm of chromosome 17 and encoding the neurofibromin protein plays a role in MPNST genesis  . MPNST is associated with neurofibromatosis from 2% to 29% of cases   . The literature shows that MPNST mainly occurs among young adults of 20 to 50 years of age   . There is no gender predominance  . Our patient was a 29 years old male. However, pediatric cases were also reported   . MPNST clinical signs are not specific. Nonetheless, symptoms often include painless swelling   . Our patient presented slow spinal cord compression, with no sign of neurofibromatosis type 1. In the literature, primary intraspinal location is extremely rare  . Plexus and large nerves are the preferential locations. NF1 associated with intraosseous MPNST is less prevalent  than with soft tissue injuries  and thus the absence of neurofibromatosis type 1 in the case of our patient. In fact, neurofibromatosis type 1 diagnosis is clinical in most cases  . There is no typical imaging of MPNST  . Our patient’s MRI helped to determine the diagnosis of spinal compression through low signal intensity on T1 and high signal intensity on T2 with bone marrow involvement. MRI remains the most advanced examination and provides information on soft tissue injuries  . Yet, some authors demonstrated that through MRI, four characteristics could determine MPNST against a neurofibroma diagnosis. They include: size ≥ 5 cm, peripheral enhancement, peri-ulcer edematous areas, and intratumoral cystic areas (hemorrhage or necrosis). If 2 to 4 criteria are observed, then there is high probability of malignancy (specificity 90%, sensitivity 61%). However, MPNST definitive diagnosis is confirmed through histology  . In our case, a biopsy was carried out along with histology which was sent in Europe, and confirmed the diagnosis 6 weeks later. This biopsy revealed a proliferation of monomorphic malignant spindle cell tumors with predominance of hemangiopericytoma structure. The tumor morphological and phenotypic profile suggested a Malignant Peripheral Nerve Sheath Tumor. Based on immunohistochemical investigation, there is no specific MPNST markers in the literature. Most commonly used markers are S-100 protein, positive in 50% of cases. Similarly, the dosage of leu-7 and myelin basic protein can be positive in 50% of cases. However HMB45 and cytokeratin are negative  . Our patient passed away a month after the tumor resection. Several other authors made the same observation about the prognosis of this medical condition     . In 1993, Seppala et al. reported that five patients with primary intradural MPNST died between 2 months and 6 years after extended metastatic surgery  . They noted that local recurrence and metastases were typical, even after an apparently complete resection. In the narrow spinal canal, radical lumpectomy with a margin of normal tissue is almost never possible without causing neurological injury. Incomplete lumpectomy and the release of highly malignant cells could be the cause of recurrence and metastases  . The poor health facilities in sub-Saharan Africa give us no other option than sending our surgical specimen abroad to refine the diagnosis. However, the too long delay-time have adverse consequences on post-surgery care and support. Although all authors agree that the treatment of Malignant Peripheral Nerve Sheath Tumor is primarily surgical  , post-surgery radiation therapy is indicated in high grade MPNST or when resection margins are invaded  . For Kar. M and al in 2006, large or deep tumors are also an indication to adjuvant radiotherapy  . We could probably overcome life-threatening condition if post survey radiation therapy was carried out. In all cases, MPNST prognosis is also poor  -  . The 5-year survival rate is 20% to 50%  . The overall development depends on the histological grade of the tumor, its size, location, whether or not it is associated with NF1, and finally the possibility and quality of primary surgery  . The risk of local recurrence is 40% to 65%  . Metastases are blood-borne or follow the pathway of nerve sheaths. Distant metastases are located in the lungs, liver and bones. They appear in an average period of two years. Such a period is shorter when there is NF1  -  .
MPNST is a rare and dreadful life-threatening disease. It presents a clinical polymorphism depending on its specific anatomic site, which can turn out to be slow spinal cord compression. But this is uncommon as MPNST has low osseous tropism. MRI remains the preferred examination for diagnosing spinal cord compression but not for MPNST. The definitive diagnosis is based on histology. In sub-Saharan Africa, the difficulties in diagnosing and the challenging post-surgery follow-up of this condition makes this tumor a life-threatening disease.
Conflict of interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
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