Adult CNS Tumors

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Pathophysiology

Summary

In adults, the most common CNS neoplasms arise from metastases, often from primary malignancies such as lung cancer, breast cancer, and melanoma. These metastases frequently present at the grey-white junction in the brain, appearing on MRI as multiple solid, nodular, ring-enhancing tumors with central necrosis. Predisposing factors for CNS tumors include exposure to ionizing radiation, especially during childhood, and certain genetic syndromes like tuberous sclerosis, neurofibromatosis 2, von Hippel-Lindau syndrome, & Turcot syndrome.

Adult CNS tumors are primarily supratentorial, involving the cerebral hemispheres, whereas pediatric tumors are primarily infratentorial. Common symptoms include headaches, fatigue, memory problems, personality changes, & seizures, resulting from compression of the surrounding brain parenchyma. Additionally, CNS tumors can produce focal deficits such as sensory loss, blindness, paralysis, gait disturbances, & ataxia. A notable complication is intracranial hypertension, attributed to either a direct mass effect or obstruction of CSF flow.

Meningiomas originate from meningeal cells in the arachnoid mater, and are benign CNS tumors. Found predominantly in women aged 40-60, these tumors typically localize in the dural folds such as the falx cerebri, tentorium cerebelli, and venous sinuses. Histologically, meningiomas are characterized by spindle cells arranged in a whorled pattern and the presence of Psammoma bodies— eosinophilic laminated calcium deposits.

Astrocytomas are the most common glioma in adults. The most malignant form, glioblastoma multiforme (GBM), or grade IV astrocytoma, is the most prevalent primary malignant CNS tumor in adults. Glioblastomas most commonly arise in men between 40-60 yrs old, and primarily affect the frontal and temporal lobes. They can present as a ‘butterfly glioma’ due to growth into the corpus callosum and across the midline and show a thick peripheral rim enhancement on MRI. Histological examination reveals small round purple cells aligning along bands of necrosis, a phenomenon termed pseudopalisading necrosis. Another defining feature is the tumor's prominent microvascular proliferation, which can precipitate hemorrhage. Both glioblastomas and oligodendrogliomas stain positive for glial fibrillary acidic protein (GFAP).

Oligodendrogliomas are slow-growing tumors that resemble oligodendrocytes, and most commonly arise between 40-50 yrs old. These tumors localize primarily in the frontal and temporal lobes and are frequently calcified. On histology, oligodendrogliomas exhibit a ‘fried egg’ appearance, characterized by round nuclei with granular chromatin and generous cytoplasm. Furthermore, their thin, fragile anastomosing capillaries create a unique ‘chicken-wire’ appearance.

Von Hippel Lindau (VHL) is an autosomal dominant genetic cancer syndrome that predisposes individuals to both CNS and non-CNS tumors. VHL results from a deletion of the VHL tumor suppressor gene on chromosome 3 and follows the ‘two-hit hypothesis,’ meaning that individuals inherit one germline mutation and acquire a somatic mutation later during their lifetime.

The most common CNS presentation in VHL is the formation of hemangioblastomas. These benign vascular lesions frequently occur in multiple CNS sites, particularly affecting the cerebellum, spinal cord (infratentorial lesions), and retina. Morphologically, hemangioblastomas are well-circumscribed vascular lesions, often surrounded by large fluid-filled cysts that contribute to the compression of adjacent tissue. Hemangioblastomas are also prone to rupture and subsequent hemorrhage due to their thin vascular walls. A defining histological feature of hemangioblastomas is their positive staining for periodic acid-Schiff (PAS). Hemangioblastomas in the retina can bleed, leading to complications such as retinal edema, traction, & detachment. VHL is also associated with conditions outside of the CNS, including clear cell renal carcinoma and pheochromocytomas.

Another entity, cavernous hemangiomas, are common in both the CNS and liver, and are characterized by clusters of thin-walled, dilated blood vessels. These hemangiomas are particularly prone to hemorrhage since their vessels contain a single endothelial layer and thin adventitia, lacking both elastic fibers and smooth muscle. This is in contrast to hemangioblastomas, which maintain a relatively normal capillary architecture that includes smooth muscle and elastic fibers.

Primary CNS lymphoma occurs when neoplastic lymphocytes proliferate in the brain rather than within a lymphoid organ. Primary CNS lymphomas is the predominant malignancy in immunocompromised patients, and is almost always associated with an EBV infection in this population. Histological evaluations typically classify them as diffuse large B cell lymphomas. Clinically, these lymphomas appear as multiple lesions that accumulate around blood vessels, with frequent areas of necrosis, and exhibit a distinctive ring enhancement on MRI.

Other notable CNS pathologies include pituitary adenomas and schwannomas. Although schwannomas predominantly form in the peripheral nervous system, they can also occur within the CNS.

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FAQs

What are the typical clinical manifestations of CNS tumors in adults?

Central nervous system (CNS) tumors in adults can manifest a range of symptoms depending on their size, location, and rate of growth. Commonly reported symptoms include persistent headaches, fatigue, memory disturbances, and notable changes in personality. Seizures may also occur due to the tumor compressing the surrounding brain tissue. Focal neurological deficits such as sensory loss, visual impairment, paralysis, gait abnormalities, and ataxia may also be observed. In certain cases, the tumor can lead to intracranial hypertension, presenting with symptoms like severe headaches, nausea, vomiting, and papilledema, which results from either the tumor's direct mass effect or an obstruction of cerebrospinal fluid (CSF) flow.

What imaging techniques are employed for CNS tumors, and how do metastases to the CNS typically appear on these images?

Magnetic resonance imaging (MRI) is the primary modality used to visualize CNS tumors due to its superior soft tissue contrast and multi-planar capabilities. When examining metastases to the CNS on MRI, they typically present as multiple solid, nodular lesions with characteristic ring enhancement. These metastatic tumors predominantly localize at the grey-white junction of the brain. A hallmark feature of these metastases is the presence of central necrosis, which contributes to their distinctive appearance on imaging.

3. What characterizes glioblastoma and how does it differ from other CNS tumors?

Glioblastoma, also known as glioblastoma multiforme (GBM) or grade IV astrocytoma, is the most common malignant primary CNS tumor in adults. It is slightly more prevalent in men and typically manifests between the fourth to sixth decades of life, usually in the frontal and temporal lobes. On MRI, glioblastomas display a thick peripheral rim enhancement and can present as a ‘butterfly glioma’ due to growth into the corpus callosum. Histologically, they show pseudopalisading necrosis and are prone to hemorrhage due to prominent microvascular proliferation.

What are the most prevalent types of CNS tumors diagnosed in adults?

In adults, meningiomas are the most commonly diagnosed CNS tumor. Originating from the arachnoid mater's meningeal cells, they are especially predominant in women between 40-60 yrs. Glioblastoma, also known as grade IV astrocytoma, is the leading malignant primary CNS tumor in adults, with a slight male predominance and usually presenting between 40-60 yrs. Astrocytomas are the most common glioma subtype. Oligodendrogliomas mirror the appearance of oligodendrocytes, and are slow-growing tumors most frequently diagnosed between aged 40-50.

What are the distinguishing features of primary CNS lymphoma?

Primary CNS lymphoma involves the proliferation of neoplastic lymphocytes in the brain, and are typically diffuse large B cell lymphomas. An immunocompromised state significantly increases the risk for CNS lymphoma, making it the most common CNS malignancy in this group, often alongside co-infection with EBV. On MRI, CNS lymphomas demonstrate ring enhancement and often accumulate around blood vessels, with areas of necrosis.