Intradural Extramedullary Benign Tumors

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Chapter 4 Intradural Extramedullary Benign Tumors

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

1 Meningioma
2 Schwannoma
3 Neurofibroma
4 Paraganglioma
5 Ganglioneuroma

INTRODUCTION

In the intradural extramedullary space, tumors from various origins can be found. Most of them are benign. Meningiomas are dural-based neoplastic proliferations of meningothelial cells. Their histologic grading is based on histologic subtype, necrosis, and mitotic rate. Their histologic variation includes meningothelial, fibrous, transitional, psammomatous, clear, chordoid, atypical, papillary, and rhabdoid subtypes.

Schwannomas are the most common spinal tumor. They are proliferations of neoplastic Schwann cells, which may have variable appearances (e.g., spindled, epithelioid, or melanotic). Schwannomas may be found throughout all levels of the spinal cord and involve the sensory nerve roots.

Neurofibromas are the proliferation of all components of a nerve, including Schwann cells, collagen, and perineurial cells. They are typically extradural lesions that may extend proximally to an intradural location.

Spinal paragangliomas arise from extra-adrenal sympathetic ganglion cells, which are composed of chromaffin cells. They are usually located at the filum terminale in the cauda equina.

Ganglioneuromas are one type of neuronal tumors in which the neoplastic cells express a mature neuronal phenotype. Most spinal ganglioneuromas involve the paraspinal region with intraspinal extension.

MENINGIOMA

EPIDEMIOLOGY

• Spinal meningiomas occur much more commonly in women than in men.
• The peak incidence of meningiomas is in the fourth to eighth decades of life.
• Multiple meningiomas occurring throughout the brain and spinal cord are often found in patients with neurofibromatosis type 2 (NF-2).

DISTRIBUTION

• Meningiomas are intradural neoplasms which may infiltrate into the adjacent spinal cord.
• Meningiomas are most commonly found in the thoracic region of the spine.

HISTOLOGY/GRADING

GENERAL

• Meningiomas are dural-based neoplastic proliferations of meningothelial cells (arachnoid cap cells).
• The classic histologic findings include lamellar (psammomatous) calcifications and nuclear pseudoinclusions, which can be found in all subtypes of this tumor.
• The neoplastic cells demonstrate uniform vimentin immunoreactivity and patchy to widespread epithelial membrane antigen (EMA) immunoreactivity.
• Adhering to the World Health Organization 2000 classification of central nervous system tumors,1 grading is based on histologic subtype and other features (e.g., necrosis, mitotic rate).
• The percentage of a higher grade histologic subtype necessary to increase the overall grade of the tumor is debatable; some neuropathologists suggest a threshold of 50% before increasing the grade.

Grade I

MENINGOTHELIAL

• The meningothelial meningioma is composed of syncytial lobules of uniform cells with oval nuclei (Fig. 4-1, A).
• The histologic differential (in small specimens) includes benign meningothelial proliferations associated with a neighboring process (e.g., a reactive response).
image image image image

Fig. 4-1 Histologic subtypes with grade I morphology. A, An otherwise low-grade meningothelial meningioma with a small focus of brain invasion. B, Fibrous meningioma composed of fascicles of spindle-shaped cells. C, Transitional meningioma with components of meningothelial (upper half) and fibrous (lower half) subtypes. D, Psammomatous meningioma composed of near confluent psammoma bodies with few intervening meningothelial cells (A-D, hematoxylin–eosin stain, ×100).

FIBROUS

• This subtype is composed of spindle-shaped meningothelial cells in a fascicular arrangement with a variable amount of interposed collagen (Fig. 4-1, B).
• The histologic differential includes solitary fibrous tumor (SFT). SFTs are immunoreactive for CD34, but non-reactive for EMA.

TRANSITIONAL

• The transitional meningioma has features of both meningothelial and fibrous subtypes with the cells commonly arranged in whorling architectural patterns (Fig. 4-1, C).
• Psammomatous calcifications are common in this subtype.

PSAMMOMATOUS

• This subtype is composed mainly of psammomatous calcifications with a paucity of cellular elements (Fig. 4-1, D).
• Psammomatous meningiomas are found most commonly in the spine.
• Even though schwannomas associated with the Carney complex, a multiple neoplasia syndrome, have a substantial psammomatous component and could be confused with this meningioma subtype, the former tumor is typically pigmented and demonstrates diffuse S100 protein and HMB-45 immunoreactivity.

Other grade I histopathologic subtypes (angiomatous, microcystic, secretory, and metaplastic) are less common in the spine.

Grade II

CLEAR CELL

• This subtype is composed of cells with clear glycogen-rich, periodic acid-Schiff–positive cytoplasm.
• The cauda equina represents a common location for clear cell meningiomas.

CHORDOID

• This subtype is composed of cords of vacuolated meningothelial cells in a mucinous matrix.
• A chordoid phenotype is most often seen as a secondary pattern within meningiomas with other histologic subtypes.
• The histologic differential includes chordoma. Whereas both meningiomas and chordomas demonstrate EMA immunoreactivity, chordomas also display strong S100 protein immunoreactivity. S100 protein immunoreactivity in meningiomas is often faint and patchy.2

Atypical

• Irrespective of the histologic subtypes previously described, a meningioma is assigned a grade II if three of the following five criteria are fulfilled:

• Sheet-like (or patternless) growth pattern (Fig. 4-2, A)
• Areas of increased cellularity
• Small cell cytology
• Tumoral necrosis (to be distinguished from necrosis associated with embolization [Fig. 4-2, B])
• Prominent (not just identifiable) nucleoli (Fig. 4-2, C)

• A grade of II is assigned if four or more mitotic figures per 10 high-power fields are identified.
• Clinicopathological studies3 have indicated that the presence of brain invasion confers a more aggressive clinical course, and this finding alone justifies a diagnosis of grade II meningioma (Fig. 4-2, D).
image image image image

Fig. 4-2 Atypical features in meningiomas. A, Patternless or sheet-like growth pattern. B, Focus of spontaneous necrosis. C, A hypercellular area containing cells with prominent nucleoli and mitotic figures. D, Glial fibrillary acidic protein immunohistochemical stain of tumor in Fig. 4-1, A highlighting brain parenchyma between the infiltrating tumor nests (×100). (A-C, hematoxylin–eosin stain; A and B, ×100; C, ×400.)

Grade III

PAPILLARY

• This subtype, commonly found in the pediatric population, is composed of cells in a pseudopapillary arrangement with a fibrovascular core.
• The histologic differential diagnosis includes ependymoma and other papillary neoplasms, which can be characterized based on immunophenotypic profiles.

RHABDOID

• The rhabdoid subtype is composed of cells with abundant eosinophilic cytoplasm and eccentrically positioned nuclei (Fig. 4-3). This meningioma subtype typically has an association with high mitotic rate and other cytoarchitectural anaplastic features, as well as evidence of brain invasion.4,5
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Fig. 4-3 Rhabdoid meningioma. Eccentrically located nuclei and abundant pinkish cytoplasm are seen (hematoxylin–eosin stain, ×400).

RADIOLOGY

• The location of meningioma is typically intradural, extramedullary. However, it is rarely located in intraosseous, extradural, or even paraspinous areas. On T1-weighted images (T1WI), the signal of the mass is isointense to the spinal cord (Figs. 4-4 and 4-5).
• On T2-weighted images (T2WI), most parts of the mass show iso-signal to the spinal cord (see Figs. 4-4 and 4-5).
• If a calcified area is included, the signal may change to low. When the meningioma is very vascular, prominent flow void can be displayed.
• With contrast material, a homogeneous enhancement pattern is common.
• A dural tail sign may be seen, which is less common than in intracranial meningiomas.
• Grossly the tumor mass is gray to white and of a slightly hard consistency (Fig. 4-6).
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Fig. 4-4 Sagittal MRI of intradural meningioma. On T2WI, a small, round mass is seen in the intradural space at the T7 level (left). The mass signal is isointense to the spinal cord. It is located in the subarachnoid space posterior to spinal cord. On T1WI, the mass signal also is isointense to the spinal cord (middle). With contrast, a homogeneous enhancement pattern is shown (right).

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Fig. 4-5 MRI axial images of intradural meningioma. On T1WI, a large iso-signal round mass is located at the posterolateral side of the intradural space (left image) with a homogeneous enhancement pattern (middle image). The spinal cord is compressed and displaced to the right anterior side. On T2 axial image adjacent caudal level to the tumor mass, a widened subarachnoid space is seen as bright high signal area (right image).

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Fig. 4-6 Intraoperative view of spinal cord meningioma. After dural opening, the arachnoid membrane is seen to cover the tumor mass. Arachnoid dissection is done. A gray to white mass of slightly hard consistency is adhered to the pial membrane of the spinal cord (left image). After resection is completed from dural attachment, en bloc removal of the tumor mass is achieved (right image).

NERVE SHEATH TUMOR—SCHWANNOMA

EPIDEMIOLOGY

• Schwannomas account for approximately 30% of all spinal tumors.
• The peak incidence for schwannomas is in the fourth to seventh decades of life.
• As with meningiomas, there is a high incidence of schwannomas in patients with NF-2.
• One variety, psammomatous melanotic schwannoma, is a characteristic manifestation of the Carney complex.6

DISTRIBUTION

• Schwannomas may be found throughout all levels of the spinal cord and involve the sensory nerve roots.
• Schwannomas may have both intradural and extradural components; an intramedullary location is rare.
• Cellular schwannomas usually are located in paravertebral locations.

HISTOLOGY/GRADING

• Schwannomas are proliferations of neoplastic Schwann cells, which may have variable appearances (e.g., spindled, epithelioid, melanotic).
• Classic schwannoma (grade I)

• Histologic sections show Antoni A (densely cellular) and Antoni B (less cellular, sometimes cystic) areas (Fig. 4-7, A).
• Within Antoni A regions, Verocay bodies (small groups of fibrils surrounded by parallel rows of neoplastic cells) are commonly found.
• Cellular atypia alone (usually in Antoni B areas) in otherwise unremarkable schwannomas reflect degenerative (so-called “ancient”) changes and confers no prognostic significance. Other reactive and degenerative features, including cyst formation, macrophage and lymphocyte infiltration, and hemosiderin-laden cells, are commonly found in Antoni B areas (Fig. 4-7, B).
• The nerve from which the schwannoma arises may be identified in the specimen and, if so, is compressed to the edge of the tumor (Fig. 4-7, C).
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