Книги по МРТ КТ на английском языке / Neurosurgery Fundamentals Agarval 1 ed 2019

and adolescents and involve the posterior arches of the vertebrae, sinuses, facial bones, skull, and mandible. These are present in up to 5% of autopsy cases. No associated chromosomal loss or translocation has been identified to date. Observation with

resection of symptomatic or enlarging lesions is recommended. En bloc surgical excision may be curative. Solitary fibrous tumors and hemangiopericytomas (SFTs/ HPC) were previously classified separately and are now recognized as the histological

Table 13.1  Simpson grading scale

VDecompression/biopsy

Abbreviations: GTR, gross total resection; STR, subtotal resection.

Note: Simpson divided meningioma resection into five grades based on the extent of resection and management of the dura and overlying bone.10 Recent refinements have included proliferative index but has not resulted in a significant deviation from the originally proposed framework.

spectrum of a single tumor entity. Heterogeneous isoto hyperdense lesions appear on noncontrast CT. Lesions are TI isointense, T2 hypointense with intense but heterogeneous contrast enhancement. GTR may be curative; subtotal resection may lead to local recurrence, which is associated with reduced survival. Malignant tumors carry a high rate of recurrence (80%) and systemic metastasis (25%), but prognosis is good for lower grades with complete surgical resection. Extended follow-up is suggested in all cases as no case of CNS SFT/ hemangiopericytoma can be considered definitively cured. Lipomas are benign lesions composed of mature adipose tissue representing 0.46 to 1% of intracranial tumors. Intracranial lesions often asymptomatic, while spinal lesions often present with cord compression and are associated with CNS dysgenesis. Lesions are midline in

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80 to 90% and usually at the surface of the corpus callosum, dorsal midbrain, cerebellar vermis, and spinal cord. As it is thought to result from the abnormal persistence and maldifferentiation of the meninx primitiva, the term lipomatous hamartoma is used interchangeably. There is marked hypodensity on CT without contrast enhancement and capsular calcification in interhemispheric lesions. They are homogeneously hyperintense on T1WI, hypointense with fat suppression, and hypointense on T2WI without enhancement. Surgery is rarely indicated and often associated with high morbidity and mortality secondary to the highly vascular nature of lipomas and their adherence to surrounding tissue.

Malignant Mesenchymal Tumors

These are rare, aggressive lesions representing less than 0.1% of intracranial tumors. Cell of origin may be pluripotent, primitive mesenchymal cells of the meninges, periadventitial spaces, tela choroidea or the stroma of the choroid plexus. Prior CNS radiation is a risk factor. EBV is associated with intracranial leiomyosarcoma in individuals with AIDS. These lesions show variable differentiation often resembling fibrous tissue (e.g., fibrosarcoma, malignant fibrous histiocytoma), muscle, cartilage, bone, or blood vessels, and are usually found in the temporal and parietal lobes. As there is a high incidence of leptomeningeal spread, imaging of the full neuraxis is essential. Systemic metastases (lungs, bone, liver) rarely occur. Radiographic appearance is often nonspecific with contrast enhancement on CT and MRI. Management strategies include maximal safe resection and radiotherapy. Chemotherapy is largely ineffective for CNS sarcomas. The 5-year survival rate was 52% overall but only 28% for patients with high-grade lesions versus 83% among patients with low-grade

lesions. Specific entities include fibrosarcomas, rhabdomyosarcomas, leiomyosarcomas, Ewing’s sarcoma (primitive neuroectodermal tumor [PNET]), osteosarcoma, Kaposi’s sarcoma, liposarcoma, angiosarcoma, and malignant fibrous histiocytoma.

radiation and temozolomide have been trialed in diffuse leptomeningeal disease. Melanocytoma is considered a WHO grade I lesion with a slow-growing indolent course and surgery may be curative. Meningeal melanomatosis typically has a dismal outcome.13

13.2.4 Hemangioblastoma

These are vascular WHO grade I tumors of unknown histogenesis associated with the leptomeninges and associated with von Hippel-Lindau (VHL).

Inactivation of the VHL tumor suppressor gene and gain of function in HIF2A have been reported in sporadic forms. Genetic changes are isolated to the stromal elements of the tumor but not the vasculature. Surgery is the mainstay of treatment if symptomatic or demonstrating growth on serial imaging. Antiangiogenic agents have been used when other modalities are not feasible.12

13.3  Neuroepithelial Brain Tumors

Neuroepithelial cells give rise to all CNS neurons and glial cells and thus neoplasms from cells of neuroepithelial origin constitute a substantial proportion of primary brain neoplasms. All tumors of glial origin are considered gliomas. The 2016 WHO classification of CNS neoplasms incorporated cytogenetics for classification of tumors with a less prominent role for histology. Isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion play an essential role in the new classification schema with additional information provided by ATRX loss, TP53 and TERT mutations.

13.2.5 Melanocytic Lesions

These include melanocytomas, malignant melanomas, and meningeal melanomatosis. They originate from leptomeningeal melanocytes and are typically found in the posterior fossa, perimedullary and high cervical cord, and less frequently, in the thoracic and lumbar spine. They are T1 hyperintense and T2 hypointense con- trast-enhancing lesions. Melanocytomas may exhibit fine punctate areas of decreased signal intensity on T1WI and show no contrast enhancement. Meningeal melanomatosis may show diffuse leptomeningeal enhancement with nodular parenchymal enhancement. The imaging characteristics vary depending on melanocytic content and hemorrhage. Treatment entails surgical resection for focal lesions;

13.3.1 Astrocytomas

Astrocytomas are gliomas derived from astrocytes and range from WHO grade I to IV.

Glioblastoma multiforme (GBM) is a WHO grade IV lesion and is the most common primary malignant CNS tumor overall representing nearly 50% of primary CNS malignancies, while pilocytic astrocytomas (WHO grade I) are the most common type in the pediatric population.14

Diffuse Infiltrating Glioma

These are WHO grade II gliomas with microscopic invasion of brain parenchyma

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and thus lack sharp boundaries. Typical MRI features include a homogeneous mass with minimal mass effect and vasogenic edema without contrast enhancement. There is T2/ fluid-attenuated inversion recovery (FLAIR) hyperintensity ( Fig. 13.4).

Lesions are hypodense on CT and sometimes calcification is present. Nearly 80% present with seizures although headaches, cognitive and behavioral changes, hemiparesis, hydrocephalus, and aphasias are other common presenting features. GTR can be difficult as a result of microscopic infiltration and some authors advocate resection of all T2 hyperintensity if this can be safely performed.

GBM shows contrast heterogeneous ring enhancement and frequently has a necrotic core ( Fig. 13.5).

Pilocytic Astrocytoma

It usually affects children although can be seen in adults. They typically occur in the cerebellum, optic nerve, or brainstem. Adult pilocytic astrocytomas follow a more aggressive clinical course compared to the pediatric population. Constitutive RAS/RAF/MAPK activation is important in the pathogenesis of sporadic pilocytic astrocytomas. CT scan characteristically shows a cystic lesion with an enhancing mural nodule. MRI reveals a solid tumor (50%) with variable contrast enhancement or cystic lesions with contrast-enhancing mural nodules (21%), mixed cystic and solid areas (29%), and occasional intratumoral hemorrhage ( Fig. 13.6).

For pilocytic astrocytomas, GTR may be curative, while subtotal resection of the nodule may provide excellent control.

Adjuvant radiotherapy and/or chemotherapy employed in lesions are not amenable to surgical resection (optic gliomas, brainstem lesions). Overall survival at 5 and 10 years is 87 and 77%, respectively.

Chordoid Glioma of the Third Ventricle

These are rare, low-grade neoplasms arising from the roof of the third ventricle or anterior wall, female preponderance, and age of onset between 30 and 70 years. The ependymal cells (tanycytes) of the lamina terminalis are their postulated source of origin. It presents with obstructive hydrocephalus, endocrine imbalance, dysautonomia, and progressive weight gain with hyperphagic behavior attributed to pressure on the surrounding suprasellar structures and hypothalamus. MRI shows a T1 isointense, T2 isoto hyperintense ovoid the third ventricular mass. Surgical resection is the treatment of choice although this can often prove difficult due the deep-seated location. Chemoand radiotherapy are not effective modalities. Outcome is often poor due to incomplete resection, associated morbidity, and high recurrence rates.

13.3.2 Pediatric Neuroepithelial Lesions

Pediatric Brainstem Glioma

These account for 25% of infratentorial CNS tumors in children with median age of 7 to 14 years. Prognosis is poor with 2-year mortality over 90%. The pons is usually the most commonly affected location followed by the medulla and midbrain. Four pathologic patterns are identified based on growth: diffuse (all are malignant), cervicomedullary (72% low-grade astrocytomas), focal (medulla with 66% low-grade astrocytomas), and dorsally exophytic (most favorable prognosis). MRI is the preferred diagnostic modality and often obviates the need for surgical biopsy, which is no longer recommended for diagnosis.

Partial resection is associated with improved survival in the first 9 months post-op for dorsally exophytic tumors.15

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Diffuse intrinsic pontine glioma (DIPG) is the most common type and is associated with a grave prognosis ( Fig. 13.7).

Palliative radiotherapy remains the mainstay of treatment for pediatric brainstem lesions. Chemotherapy has not proven very beneficial.

A new entity called “diffuse midline glioma, H3K27 mutant” has been defined which includes tumors previously referred to as DIPG. It was included in the WHO 2016 classification of CNS tumors. The mutation is found in 71% of patients with DIPG. Radiotherapy is the standard treatment and leads to neurologic improvement and improved progression-free survival without improvement in overall survival. Median survival is less than 12 months.16,​17

Tectal Glioma

These are typically low-grade gliomas arising from the tectal plate of the midbrain and account for 6% of surgically treated brain tumors in children. Median age of presentation is 6 to 10 years. Management is usually conservative with treatment of hydrocephalus. Stereotactic radiosurgery often offered for progressive lesions. Outcome is generally favorable with median interval of tumor progression of 7.8 years from the time of shunt insertion and 11.5 years from initial presentation in a sin- gle-institution series.18,​19

Pilocytic Myxoid Astrocytoma

Pilomyxoid astrocytoma was introduced first in 1985 as “diencephalic pilocytic astrocytoma with clinical onset in infancy.” Median age of onset is 10 to 18 months. Histologically, the tumor appears similar

to pilocytic astrocytomas with the addition of a prominent myxoid matrix. Outcomes are poor compared to classical pilocytic astrocytoma with lower progres- sion-free survival (38.7% at 1 year vs. 69.2% for classic pilocytic astrocytomas).20,21

13.3.3 Other Low-Grade Glial Tumors

Angiocentric Glioma

Angiocentric glioma is a tumor entity defined in 2005. Refractory epilepsy is the most common presenting feature. The mean age at presentation is 17 years. They are often located in the frontoparietal region, temporal lobe, and hippocampus. MRI reveals a T1 hypointense, T2 hyperintense, nonenhancing well-circumscribed mass with a stalk-like extension to the subjacent ventricle. GTR is potentially curative and there is no established role for chemoradiotherapy.

Histological analysis of an angiocentric glioma reveals bipolar cells with an angiocentric growth pattern and pseudorosettes reminiscent of ependymoma.

Astroblastoma

These are rare tumors that arise from astroblasts with a mean age of presentation between 10 and 30 years. Lesions are large, peripherally located, supratentorial, lobulated, solid, cystic masses with little vasogenic edema and tumor infiltration. Multiple cysts are commonly seen giving rise to a bubbly appearance. Lesions are isointense on T1 and T2 with calcifications in 85% of lesions on CT. Resection with adjuvant radiotherapy improves survival in patients with highgrade lesions.22

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13.4  Ependymoma and Subependymoma

Ependymomas arise from ependymal cells lining the cerebral ventricles or central canal of the spinal cord. They are most common in children and young adults without gender predilection. They are T1 isoand T2 isoto hyperintense with heterogeneous contrast enhancement with frequent intratumoral hemorrhage, calcification, and cysts ( Fig. 13.8).

Supratentorial ependymoma has RELA- or YAP1 fusion, which activate nuclear factor kappa B (NF-κB) pathway. Standard treatment is maximal safe resection followed by radiation therapy. The efficacy of chemotherapy remains controversial. Fiveyear survival is 70 to 90% and 60 to 65% for grades II and III tumors, respectively.

Subependymomas in contrast occur in older individuals and present as a sharply demarcated isoor hypodense lesion on CT with occasional calcification. They are hypoto isointense on T1 and hyperintense on T2-weighted MRI without contrast enhancement. These are considered benign lesions and management includes surgical resection without adjuvant therapy. Prognosis is good in the setting of a GTR.14

13.5  Pineal Region Tumors

The most frequent tumor in the pineal region is a germ cell tumor (35.3%), followed by pineal parenchymal tumor (PPT) (27.9%). PPTs consist of pineocytoma (WHO grade I), pineal parenchymal tumor of intermittent differentiation (PPTID) (WHO grade II/III), pineoblastoma (WHO grade IV), and papillary tumor of the pineal region (PTPR) (WHO grade II/III). Pineocytoma occurs in patients from 10 to 60 years, with a slight predominance in females. It presents with intracranial

hypertension due to obstructive hydrocephalus caused by compression of the mesencephalic aqueduct. It usually presents as globular, well-demarcated masses with occasional cysts. CT shows calcification usually in the periphery of the mass. Complete resection may lead to cure. If residual tumor is observed postoperatively, local radiation therapy is usually done. Pineoblastomas are WHO grade IV neoplasms, which arise from pineal parenchymal cells. They occur in children and young adults without gender predilection. The standard treatment is surgical resection followed by whole-brain radiation therapy and multiagent chemotherapy. In adult patients, GTR and radiation therapy with more than 40 Gy improves the prognosis. Papillary tumors of the pineal region are WHO grade II or III tumors thought to arise from ependymal cells at the subcommissural organ. They occur in all ages but most frequently in young adults without gender predilection. Treatment is resection, then radiation therapy with chemotherapy reserved for recurrence or CSF dissemination.30,​31

13.6  Embryonal/PNETs

13.6.1 Medulloblastoma

Medulloblastomas comprise 15 to 20% of pediatric brain tumors. Approximately 75% occur in children younger than 15 years with a peak age of 7 years and a male:female ratio of 2:1. They are composed of small primitive neuroepithelial cells thought to arise from the external granular layer or subependymal matrix cells at superior and inferior velum. The cerebellar vermis and fourth ventricles are involved in 75% and the cerebellar hemispheres in 25%. These are WHO grade IV invasive tumors and 10 to 35% present with subarachnoid dissemination. The tumor appears as a well-circumscribed solid mass in the cerebellar vermis, hemisphere, or fourth ventricles. CT shows a high-density mass due to high cellularity. The lesions are hypoto isointense on T1, isoto hyperintense on T2, and enhance on gadolinium T1-weighted images. There is restricted diffusion on diffusion-weighted imaging (DWI) ( Fig. 13.9).