Chapter 7 Intramedullary Tumors

Jae-Soo Koh, Ung-Kyu Chang, Terri Haddix

1 Astrocytoma

2 Ependymoma

3 Capillary Hemangioblastoma

4 Spinal Cord Cavernous Angioma

5 Ganglioglioma

6 Neurocytic Tumors

7 Oligodendroglioma

8 Embryonal Neoplasms

9 Spinal Cord Intramedullary Metastasis

INTRAMEDULLARY TUMORS

Spinal cord intramedullary tumors are mostly benign. Primary intramedullary tumors originate from glial cell, neuronal cell, or other connective tissue cells. Glial tumors are astrocytoma, ependymoma, and oligodendroglioma. Astrocytomas are neoplasms of astrocytic origin within the spinal cord which demonstrate immunoreactivity for glial origin cells. They infiltrate into the surrounding spinal cord tissue, which makes radical resection difficult. Ependymomas, another glial tumor, are from the ependymal lining cells of the central canal in the spinal cord. They rarely show infiltrative growth pattern. Oligodendrogliomas are composed of proliferations of neoplastic oligodendroglial cells.

Intramedullary tumors from vascular tissue are hemangioblastomas and cavernous angiomas. Spinal cord hemangioblastomas are vascular neoplasms of benign nature that occur sporadically or in association with von Hippel–Lindau (VHL) disease. They are usually attached to the pial surface. Cavernous angiomas are composed of thin-walled, dilated, abnormal, vascular channels without neural tissue.

Tumors of neuronal components are gangliogliomas, neurocytomas, and embryonal neoplasms. Gangliogliomas are composed of both glial and neuronal neoplastic cells. The glial component is typically piloid to fibrillary, and a dysplastic neuronal portion also is identified.

Embryonal neoplasms correspond to primitive neuroectodermal tumors (PNETs), and neurocytic tumors are matched with central neurocytomas in the brain.

Metastatic lesions are rarely seen in the spinal cord and result from vascular rather than subarachnoid spread.

ASTROCYTOMA

EPIDEMIOLOGY

• Intramedullary spinal cord astrocytomas represent 6–8% of spinal cord tumors.¹

• In the pediatric population this tumor is the most common glial neoplasm and is typically low grade.²

• In adults, astrocytomas are the second most common glial spinal cord neoplasm after ependymomas.

• Pilocytic astrocytomas of the spinal cord are associated with neurofibromatosis type 1 (NF-1).

DISTRIBUTION

• Astrocytomas may involve any region of the spinal cord, although the cervical area is most commonly affected in children.²

• Holocord involvement may occur.

HISTOLOGY/GRADING

General

• These tumors are composed of neoplastic astrocytes that demonstrate immunoreactivity for glial fibrillary acidic protein (GFAP).

• GFAP immunoreactivity may be lost in some high-grade astrocytomas (e.g., glioblastomas and gliosarcomas).

Pilocytic Astrocytoma (Grade I)

• The classic histologic phenotype is of a biphasic neoplasm composed of looser (and cystic) areas with protoplasmic astrocytes and densely cellular areas composed of hair-like (piloid) cells (Fig. 7-1).

• Eosinophilic granular bodies (Fig. 7-2) are more commonly found in loose areas, whereas Rosenthal fibers (Fig. 7-3) predominate in densely cellular areas.

• Oligodendroglial-like cells (cells with rounded nuclei and perinuclear clearing) may be prominent in some regions (Fig. 7-4).

• Pilocytic astrocytomas (PAs) are associated with NF-1.

• The histologic differential includes gliosis (particularly when only densely cellular areas are sampled) and rarely occurring oligodendrogliomas or other tumors with clear cell histology (e.g., ependymoma).

Fig. 7-1 Classic histologic appearance of pilocytic astrocytoma (hematoxylin–eosin stain, ×200).

Fig. 7-2 Eosinophilic granular body in a less cellular area of a pilocytic astrocytoma (hematoxylin–eosin stain, ×400).

Fig. 7-3 Rosenthal fibers in a densely cellular area of a pilocytic astrocytoma (hematoxylin–eosin stain, ×200).

Fig. 7-4 A prominent oligodendroglial-like phenotype in one area of a pilocytic astrocytoma (hematoxylin–eosin stain, ×200).

Diffuse Astrocytoma (Grade II)

• This neoplasm shows relatively low cellularity and is composed of cells with angulated nuclei and modest nuclear pleomorphism (Fig. 7-5).

• The neoplastic astrocytes may have varied appearances, including fibrillary or gemistocytic (plump).

• Low mitotic activity without evidence of microvascular proliferation or pseudopalisading necrosis is characteristic.

• The histologic differential includes ganglioglioma if infiltrated gray matter is sampled. The presence of a population of clearly dysplastic ganglion cells should be sought to make the diagnosis of ganglioglioma.

Fig. 7-5 A fibrillary astrocytoma infiltrating gray matter. Note the neurons with large nuclei and prominent nucleoli in the left upper and center fields of the figure (hematoxylin–eosin stain, ×200).

Anaplastic Astrocytoma (Grade III)

• The histologic features are similar to the grade II tumors just described, but with the presence of increasing cellularity and mitotic activity.

• No microvascular proliferation or pseudopalisading necrosis is seen.

Glioblastoma (Grade IV)

• Features of anaplastic astrocytoma (Fig. 7-6) with microvascular proliferation and/or pseudopalisading necrosis (Fig. 7-7).

• Leptomeningeal seeding may occur with higher grade astrocytomas.

• Occasionally true sarcomatous differentiation may be found (gliosarcoma), but these tumors typically involve the cerebral hemispheres.

• Small cell glioblastoma may be confused with an anaplastic oligodendroglioma. Cytogenetic analyses may help distinguish these tumors. Many oligodendrogliomas demonstrate deletions of the short and long arms of chromosome 1 (1p) and chromosome 19 (19q), respectively, and amplification of the epidermal growth factor receptor gene is found in some small cell glioblastomas.

Fig. 7-6 Cytologic features of increased cellularity and mitotic figures shared by grades III and IV astrocytomas (hematoxylin–eosin stain, ×400).

Fig. 7-7 The presence of pseudopalisading necrosis (upper center) and/or microvascular proliferation (lower two-thirds) distinguish grade IV from grade III astrocytomas (hematoxylin–eosin stain, ×100).

RADIOLOGY

• Magnetic resonance imaging (MRI) shows enlargement of the cord at the tumor location.

• Astrocytoma shows slightly low signal or iso-intensity relative to the cord on T1-weighted images (T1WI) and high signal on T2-weighted images T2WI) (Fig. 7-8).

• After injection of intravenous gadolinium, no enhancement of the intramedullary mass is noted. Syringomyelia and hemorrhage are not found.

• Reactive or neoplastic cysts are identified in high-grade glioma.³

Fig. 7-8 MRI showing diffusely widened spinal cord extending from C1 to C5 in low-grade astrocytoma. Sagittal T2WI (left) shows high signal intensity, sagittal T1WI (center) low signal intensity, and enhanced image (right) a slightly enhanced lesion.

EPENDYMOMA

EPIDEMIOLOGY

• In the pediatric population, ependymomas are nearly always intracranial in location.

• The peak incidence of spinal ependymomas is in the fourth and fifth decades of life.¹

• Spinal intramedullary ependymoma arises from the central canal and accounts for 1.5–3% of central nervous system (CNS) tumors.

• Ependymoma accounts for 15% of all spinal cord tumors, comprises 60% of spinal gliomas, and is known to be the most common intramedullary spinal cord tumor in adults.

DISTRIBUTION

• Ependymomas may be found at any region of the spinal cord, although cervical and cervicothoracic segments are slightly more favored.

• Myxopapillary ependymomas have a predilection for the filum terminale and conus medullaris.

HISTOLOGY/GRADING

Most spinal ependymomas are histologically benign and rarely show infiltrative growth. Though they do not form tumor capsules, the interface between the tumor mass and the surrounding normal cord tissue is relatively well defined.⁴

General

Ependymomas demonstrate cytoplasmic GFAP immunoreactivity. Both punctate intracytoplasmic and ring-like epithelial membrane antigen (EMA) immunoreactivity have been reported in ependymomas.^5,6

Myxopapillary Ependymoma (Grade I) (Fig. 7-9)

• These tumors demonstrate a papillary architecture composed of vessels covered by a layer of monomorphic cells and separated by pools of mucin.

• An eosinophilic aggregate is often seen within the mucin.

Fig. 7-9 The classic histologic appearance of a myxopapillary ependymoma (hematoxylin–eosin stain, ×200).

Ependymoma (WHO Grade II)

• This grade of ependymoma is composed of monomorphic cells with little mitotic activity.

• The cells often aggregate with processes extending to centrally positioned vessels forming perivascular pseudorosettes (Fig. 7-10).

• True ependymal rosettes (tumor cells aligned to form a true central lumen) are uncommon.

• Microvascular proliferation and sheet-like growth patterns are not found to an appreciable degree.

• Histologic variants include clear cell, tanycytic, and papillary.

• Areas of calcification and hyalinization may be found.

• Depending on the degree of sampling, the histologic differential can include other clear cell neoplasms (e.g., oligodendroglioma) and other papillary neoplasms (e.g., choroid plexus lesions), all of which should be distinguishable based on their immunohistochemical profiles.

Fig. 7-10 Perivascular pseudorosettes are prominent in this example of a grade II ependymoma (hematoxylin–eosin stain, ×200).

Ependymoma (Grade III)

High-grade ependymomas demonstrate greater cellularity, a sheet-like growth pattern, increasing mitotic activity, nuclear anaplasia, and microvascular proliferation, as compared with grade II neoplasms. It may be difficult in some circumstances to distinguish high-grade ependymomas from grade IV astrocytomas.

RADIOLOGY

• Spinal intramedullary ependymoma usually shows low-signal intensity on T1WI and high-signal intensity on T2WI MRI (Figs. 7-11 and 7-12).

• It has good contrast enhancement and a well-demarcated margin, but the signal intensity and the degree of enhancement are variable because of the different distributions of the vascular component of the connective tissue in the tumor mass (Figs. 7-13 to 7-15).⁷

• Homogeneous enhancement is observed in 47% of tumors and heterogeneous enhancement in 53%. In most cases, the interface between the tumor and the spinal cord is clearly identified.

• Associated syrinx is commonly seen in intramedullary ependymomas. It is known that tumor syrinx occurs in more than 50% of cases of intramedullary ependymomas, which is greater than the incidence of syrinx in spinal astrocytomas.

• The more proximally located the tumor mass, the more often tumor syrinx tends to develop.⁸

• Syrinx is more commonly found on the cephalic side of the tumor mass than on the caudal side and at the cervical level rather than the thoracolumbar level. These tendencies suggest that the development of the syrinx may be related to the cerebrospinal fluid circulation.⁹

• The presence of syrinx in intramedullary spinal cord tumors is known to be a good prognostic factor because it enables complete resection of the tumor mass with the provision of an excellent dissection margin between the tumor mass and normal cord tissue.

• A tumor cyst is found in 43% of cases. Low-signal intensity on T2WI suggests repeated hemorrhage.

Fig. 7-11 T2 sagittal MR of myxopapillary ependymoma at conus level. High signal mass is encroaching the L1 vertebral body. In the tumor mass, serpentine structures (feeding vessels) are seen.

Fig. 7-12 T1 sagittal MR of myxopapillary ependymoma. The mass signal is isointense to the spinal cord.

Fig. 7-13 With gadolinium use, the mass shows bright enhancement.

Fig. 7-14 On the axial view at the L1 vertebral body level, intradural mass is extending to posterior portion of the vertebral body.

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