Tumors of the CNS

Pituitary adenomas are tumors that develop within the anterior lobe of the pituitary gland. They are classified by size (either micro- or macroadenomas) and by their ability to secrete hormones. Non-functioning or non-secretory adenomas do not secrete hormones but can compress surrounding pituitary tissue, leading to hypopituitarism. Secretory adenomas secrete various hormones depending on the cell type from which they evolved, leading to hyperpituitarism.

Astrocytomas are neuroepithelial tumors that arise from astrocytes, which are star-shaped glial cells (supporting tissues of the CNS). Astrocytomas are a type of glioma. There are 4 grades of astrocytomas. Grade I tumors are typically benign and present in children, while grade IV tumors (known as glioblastoma multiforme) are the most common primary malignant brain tumor in adults and have a particularly poor prognosis. The etiology of astrocytomas is usually unknown. The exact presenting symptoms depend on the tumor location and grade, but patients may exhibit headaches, seizures, and/or focal neurologic deficits. Diagnosis is made by MRI and tissue biopsy. Treatment depends on the grade of the tumor and may include any combination of surgery, radiation therapy, and/or chemotherapy.

Medulloblastomas are malignant primitive neuroectodermal tumors that arise in the posterior fossa in children. Medulloblastomas are the most common malignant brain tumors in children. Patients with medulloblastoma present with symptoms of increased intracranial pressure and cerebellar signs, which both evolve and worsen over weeks to a few months. Magnetic resonance imaging is the imaging modality of choice and typically shows a midline or paramedian cerebellar mass that enhances with contrast, but histopathological analysis after surgical resection is required for diagnosis. Treatment involves a combination of surgery, radiation therapy, and chemotherapy. Prognosis depends on a variety of factors, but with modern multimodality therapy, roughly 75% of children diagnosed with medulloblastoma survive into adulthood.

Meningiomas are slow-growing tumors that arise from the meninges of the brain and spinal cord. The vast majority are benign. These tumors commonly occur in individuals with a history of high doses of skull radiation, head trauma, and neurofibromatosis 2. Clinical symptoms of meningioma depend on the location and progression of the tumor, with a large proportion of meningiomas being asymptomatic. When symptoms do develop, they most commonly include headache, seizures, visual disturbances, and other focal neurologic deficits. Diagnosis is made based on neuroimaging (MRI is the gold standard) and biopsy. Management involves surveillance for asymptomatic patients and, for symptomatic patients, surgical resection. Radiation is also used in some cases.

Schwannomas (also known as neurilemmomas) are benign nerve sheath tumors in the peripheral nervous system (PNS), arising from Schwann cells that encase the peripheral nerves. Schwannomas are the most common tumors in the PNS. Although schwannomas are typically sporadic, they can be associated with neurofibromatosis type II and schwannomatosis. The clinical presentation of schwannomas depends on their specific location, but general signs and symptoms include a palpable mass on the skin, pain, and/or paresthesias due to nerve compression. The diagnosis is established primarily based on imaging studies (MRI or CT), and the treatment is usually surgical resection.

Acoustic neuroma, also referred to as vestibular schwannoma, is a benign tumor arising from Schwann cells of the vestibular component of the cranial nerve VIII. Acoustic neuroma forms within the internal auditory meatus and extends into the cerebellopontine angle. Vestibular schwannoma is mostly unilateral. Bilateral vestibular schwannomas are associated with neurofibromatosis type II. Symptoms arise due to compression of the cranial nerves V, VII, and VIII, and the cerebellum. The most common complaint is unilateral hearing loss but acoustic neuroma can also present with vertigo, decreased facial sensation, Bell’s palsy, and ataxia. Diagnosis of vestibular schwannoma is made with MRI of the brain with contrast. Treatment depends on the size of the tumor and symptom severity. Large tumors with severe hearing loss are treated with surgical excision or radiation therapy, while small tumors with mild symptoms can be observed over time.

Oligodendrogliomas are malignant CNS tumors arising from neural glial cell precursors. Oligodendrogliomas often arise in the frontal lobes of the brain and have a generally favorable prognosis when compared to other gliomas. Oligodendrogliomas are the 3rd most common CNS tumor. The most frequent presenting symptom is a seizure; other symptoms include headaches, visual loss, and focal neurologic deficits. Diagnosis is established by brain biopsy that demonstrates a classic “fried egg” appearance (round nuclei with clear cytoplasm). Oligodendrogliomas are slow-growing, but because they are life-limiting, they are managed with a combination of surgical resection, radiation, and chemotherapy.