Intradural Extramedullary Malignant Tumors

Chapter 6 Intradural Extramedullary Malignant Tumors



Jae-Soo Koh, Ung-Kyu Chang, Se-Hoon Kim, Terri Haddix



1 Malignant Peripheral Nerve Sheath Tumor

2 Hemangiopericytoma

3 Leptomeningeal Metastasis


INTRODUCTION


In the intradural extramedullary space, malignant tumors rarely occur. The malignant nerve sheath tumors are malignant lesions of neural origin involving spinal root, neural axis, peripheral nerve, and end organs. They are generally regarded as being of Schwann cell origin.


Hemangiopericytomas are hypervascular tumors arising from the pericyte, a modified smooth muscle cell that normally surrounds reticular sheath capillaries and postcapillary venules. They are also called angioblastic meningioma.


The dissemination of cancer cells within the spinal subarachnoid space is a devastating complication of systemic cancer, which is a feature of advanced stages of disease. Leptomeningeal metastasis is a systemic complication of cancer within the spinal subarachnoid space at an advanced stage.



MALIGNANT PERIPHERAL NERVE SHEATH TUMOR



EPIDEMIOLOGY



• Neurogenic tumors may arise from peripheral nerves or nerve sheaths, or from sympathetic ganglions.

• The tumors that arise from peripheral nerves or nerve sheaths include neurofibroma, neurilemmoma (schwannoma), and malignant nerve sheath tumors. Tumors from sympathetic ganglions are ganglioneuroma, ganglioneuroblastoma, and neuroblastoma. Nearly 85% of tumors in children are ganglion in origin whereas, in adults, more than 75% are nerve sheath tumors.1

• In varying proportions, neurogenic tumors also may be malignant. These tumors are variously termed malignant schwannoma, neurogenic sarcoma, or neurofibrosarcoma, but malignant peripheral nerve sheath tumor (MPNST) is the preferred designation.


DISTRIBUTION



• The majority of MPNSTs are derived from neurofibroma or arise de novo in normal peripheral nerves.2,3

• There were only very rare cases arising in malignant transformation of benign schwannoma or sympathetic ganglion tumors.4 Large and medium-sized nerves are more often involved than small nerves. Common sites of origin include the sciatic nerve, brachial plexus, and upper arm. MPNSTs affect young to middle-aged adults, with a slight female predominance.

• Neurofibromatosis type 1 (NF-1) predisposes to the development of MPNSTs. About 50–60% of MPNSTs occur in patients with NF-1.2,3 In addition to hereditary factors, exposure to ionizing radiation also may play a role in the development of MPNSTs.


HISTOLOGY



• The malignant nerve sheath tumors are confined to the cells intrinsic to the peripheral nerve sheath, including the perineurium and endoneurium. These tumors are generally regarded as being of Schwann cell origin because most of them usually exhibit some evidence of Schwann cell differentiation and the small minority have the features of fibroblast or perineurial cells.

• Histologically, MPNSTs are usually more hypercellular with spindle cell proliferation. The tumor cells often show hyperchromatic nuclei and are mitotically active.4

• Microscopically, the tumor shows fasciculated growth of tightly packed, hyperchromatic spindle cells (Fig. 6-1). The fibrosarcoma-like fascicles are focally alternating with hypocellular myxoid zones, creating a marbleized appearance. Focal, subtle nuclear palisading and waving nuclei are present. Moderate cellular atypism, high mitotic activity, and foci of necrosis are also noted (Fig. 6-2).

• In the immunohistochemical studies, the tumor cells are positive for S100 and negative for cytokeratin, desmin, and CD34. Positive p53 immunoreactivity is noted in 10% of tumor cells.

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Fig. 6-1 Low-power photomicrograph of malignant peripheral nerve sheath tumor shows spindle to ovoid tumor cells with fascicular arrangement (hematoxylin–eosin stain, ×40).


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Fig. 6-2 High-power photomicrograph of MPNST shows buckle-like irregular nuclear shape (hematoxylin–eosin stain, ×400).



RADIOLOGY



• Imaging findings with MPNST are not specific and can mimic metastatic lesions to the vertebrae.

• On plain radiographs, nerve sheath tumors typically appear as sharply marginated, round, elliptical, or lobulated paraspinal masses. Intervertebral foramen widening is seen and erosion of the ribs and vertebral bodies sometimes is evident5 (Fig. 6-3).

• On computed tomography (CT) scan, schwannoma has been shown to have a mixed attenuation, attributable to a confluent area of hypocellularity adjacent to dense cellularity, or xanthomatous change, or regions of cystic degeneration. Variable enhancement of the tumor may be seen after contrast infusion. Calcification (about 5–10%) may be present with either benign or malignant tumors but is not a reliable sign of benign character.

• On magnetic resonance imaging (MRI), MPNSTs typically have iso-signal intensity as muscle on T1-weighted images (T1WI) and markedly increased signal intensity on T2-weighted images (T2WI) or contrast-enhanced images, although often in an inhomogeneous fashion (Figs. 6-4 to 6-7).

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Fig. 6-3 Plain radiography (left) and CT scan (right) of MPNST. Compression fracture of T7 and T8 and mild scoliotic deformity are seen on plain radiography. On CT scan, an osteolytic lesion invades the vertebral body and epidural mass formation is observed. On the margin of the tumor mass, an osteosclerotic bony margin is formed (right).


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Fig. 6-4 MRI sagittal view of MPNST. On T2WI, a mixed high signal intensity mass is seen in the T7, T8 vertebral body and epidural space. The spinal cord is compressed from the posterior side (left). Diffuse low signal change of the T7, T8 vertebral body is observed on T1WI (middle). An epidural mass is easily delineated from the epidural fat. With gadolinium use, a homogeneous enhancement pattern is shown (right).


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Fig. 6-5 Axial MRI of MPNST at T7. Tumor mass surrounds the spinal cord and constricts the entire dura. Epidural mass is connected with an intraosseous mass at T7.


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Fig. 6-6 Another case of the MPNST at T10. On the sagittal view of MRI, the signal of the mass is mixed (T2WI; left), diffuse low (T1WI; middle), and dense enhancement pattern (right). On T1WI, the T10 vertebral body shows no signal change. The mass abuts the posterior cortex of the vertebral body. The tumor does not infiltrate the vertebral body.


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Fig. 6-7 Axial view of T10 MPNST. The location of the tumor mass is purely extradural. The mass grows into posterior back muscle, but the lamina is not destroyed. The signal of the mass is the same as that in the sagittal view. The posterior cortex of the vertebral body is slightly displaced and eroded but not destroyed.

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Extradural Benign Tumors Anterior Approaches to the Cervicothoracic Junction Lateral Approaches to Cervicothoracic Junction Management of Upper Cervical Spine Tumors Posterior Stabilization in the Cervical Spine and Cervicothoracic Junction Radiographic Evaluation of Lesions within the Vertebrae

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Aug 6, 2016 | Posted by in NEUROSURGERY | Comments Off on Intradural Extramedullary Malignant Tumors

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