Tumors Of The Cns And Pns are shown in Figure

A. One-third of brain tumors are metastatic, and two-thirds are primary. In metastatic tumors, the primary site of malignancy is the lung in 35% of cases, the breast in 17%, in the gastrointestinal tract in 6%, melanoma in 6%, and the kidney in 5%.

B. Brain tumors are classified as glial (50%) or nonglial (50%).

C. According to national board questions, the five most common brain tumors are:

1. Glioblastoma multiforme, the most common and most fatal type

2. Meningioma, a benign noninvasive tumor of the falx and the convexity of the hemisphere

3. Schwannoma, a benign peripheral tumor derived from Schwann cells

4. Ependymoma, which is found in the ventricles and accounts for 60% of spinal cord gliomas

5. Medulloblastoma, which is the second most common posterior fossa tumor seen in children and may metastasize through the CSF tracts

XIII. CUTANEOUS RECEPTORS (Figure 5-3) are divided into two large groups: free nerve endings and encapsulated endings.

A. Free nerve endings are nociceptors (pain) and thermoreceptors (cold and heat).

B. Encapsulated endings are touch receptors (Meissner's corpuscles) and pressure and vibration receptors (Pacinian corpuscles).

C. Merkel disks are unencapsulated light touch receptors.

Germinomas

• germ cell tumors that are commonly seen in the pineal region (>50%)

• overlie the tectum of the midbrain

• cause obstructive hydrocephalus due to aqueductal stenosis

• the common cause of Parinaud's syndrome

Brain abscesses-

• may result from sinusitis, mastoiditis, hematogenous spread

• location: frontal and temporal lobes, cerebellum

• organisms: streptococci, staphlococci. and pneumococci

• result in cerebral edema and herniation

Colloid cysts of third ventricle

• comprise 2% of intracranial gliomas

• are of ependymal origin

• found at the interventricular foraminia

• ventricular obstruction results in increased intracranial pressure, and may cause positional headaches, "drop attacks,"

or sudden death

Third Ventricle Glioma

Choroid plexus papillomas

• histology: benign; no necrosis or invasive features

• represent 2% of the gliomas

• one of the most common brain tumors in patients < 2 years of age

• occur in decreasing frequency: fourth, lateral, and third ventricle

• CSF overproduction may cause hydrocephalus

Cerebellar astrocytomas

• benign tumors of childhood with good prognosis

• most common pediatric intracranial tumor

• contain pilocytic astrocytes and Rosenthal fibers

Medulloblastomas-

• represent 7% of primary brain tumors

• represent a primitive neuroectodermal tumor (PNET)

• second most common posterior fossa tumor in children

• responsible for the posterior vermis syndrome

• can metastasize via the CSF tracts

• highly radiosensitive

Hemangioblastomas

• characterized by abundant capillary blood vessels and foamy cells: most often found in the cerebellum

• when found in the cerebellum and retina, may represent a part of the von Hippel-Lindau syndrome

• 2% of primary intracranial tumors: 10% of posterior fossa tumors

Meningiomas

• derived from arachnoid cap cells and represent the second most common primary intracranial brain tumor after astrocytomas (15%)

• are not invasive; they indent the brain; may produce hyperostosis

• pathology: concentric whorls and calcified psammoma bodies

• location: parasagittal and convexity

• associated with neurofibromatosis-2 (NF-2)

Astrocytomas

• represent 20% of the gliomas

• histologically benign

• diffusely infiltrate the hemispheric white matter most common glioma found in the posterior fossa of children

Glioblastoma multiforme

• represents 55% of gliomas

• malignant: rapidly fatal astrocytic tumor

• commonly found in the frontal and temporal lobes and basal ganglia

• frequently crosses the midline via the corpus callosum (butterfly glioma)

Oligodendrogliomas . mç)§t common primary brain tumQr

• represent 5% of all . histology: pseudopalisades, the gliomas perivascular pseudorosettes

• grow slowly and are relatively benign

• most common in the frontal lobe

• calcification in 50% of cases

• cells look like "fried eggs" (perinuclear halos)

Intraspinal tumors ----

• Ependymomas represent 60% of intramedullary gliomas

Pituitary Adenoma Visual Field Defect

Craniopharyngiomas

• represent 3% of primary brain tumors

• derived from epithelial remnants of Rathke's pouch

• location: suprasellar and inferior to the optic chiasma

• cause bitemporal hemianopia and hypopituitarism

• calcification is common

Pituitary adenomas (PA)

• most common tumors of the pituitary gland

• prolactinoma is the most common (PA)

• derived from the stomodeum (Rathke's pouch)

• represent 8% of primary brain tumors

• may cause hypopituitarism, visual field defects (bitemporal hemianopia and cranial nerve palsies CNN III, IV, VI. V-1 and V-2, and postganglionic sympathetic fibers to the dilator muscle of the iris)

Schwannomas (acoustic neuromas)

• consist of Schwann cells and arise from the vestibular division of CN VIII

• comprise approx. 8% of intracranial neoplasms

• pathology: Antoni A and B tissue and Verocay bodies

• bilateral acoustic neuromas are diagnostic of NF-2

— Brain stem glioma

• usually a benign pilocytic astrocytoma

• usually causes cranial nerve palsies may cause the "locked-in" syndrome

Ependymomas

• represent 5% of the gliomas

• histology: benign, ependymal tubules, perivascular pseudorosettes

• 40% are supratentorial; 60% are infratentorial (posterior fossa)

• most common spinal cord glioma (60%)

• third most common posterior fossa tumor in children and adolescents

Figure 5-2. Tumors of the central and peripheral nervous systems. (A) Supratentorial tumors. (J3) Infratentorial (posterior fossa) and intraspinal tumors. In children, 70% ol tumors are infratentorial. In adults, 70% of tumors are supratentorial. CN = cranial nerve; CSF = cerebrospinal fluid.

Free nerve endings

Meissner corpuscles Merkel cells

Schwann cells

Dermal Free Nerve Endings

y Epidermis y Dermis

Basement membrane

Merkel disk

Cutaneous nerve

A-p fiber

Pacinian corpuscles

Adipose tissue

Figure 5-3. Four important cutaneous receptors. Free nerve endings mediate pain and temperature sensation. Meissner corpuscles of the dermal papillae mediate tactile two-point discrimination. Paccinian corpuscles of the dermis mediate touch, pressure and vibration sensation. Merkel disks mediate light touch.

Free nerve endings y Epidermis y Dermis

Meissner corpuscles Merkel cells

Cutaneous nerve

A-p fiber

Basement membrane

Pacinian corpuscles

Adipose tissue

Schwann cells

Merkel disk

Figure 5-3. Four important cutaneous receptors. Free nerve endings mediate pain and temperature sensation. Meissner corpuscles of the dermal papillae mediate tactile two-point discrimination. Paccinian corpuscles of the dermis mediate touch, pressure and vibration sensation. Merkel disks mediate light touch.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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