Color Atlas of Neurology

T2

T5

Afferent pathway (thermoreceptors)

Pregan-

glionic sudoriparous fibers (T2/3-L2/3)

Innervation of sweat glands

Extrinsic vagal and sympathetic efferent fibers (CNScontrolled)

Bladder Function

The urinary bladder stores (continence) and voids (micturition) the urine produced by the kidneys. Parasympathetic fibers arising in segments S2–S4 (sacral micturition center, detrusor nucleus) and traveling through the pelvic plexus activate the detrusor muscle of the bladder. Sympathetic fibers arising from segments T10– L2 and traveling through the hypogastric plexus inhibit the detrusor (!-adrenergic receptors) and stimulate the vesical neck (trigone, internal sphincter; α-adrenergic receptors). Somatic motor impulses arising from segments S2–S4 (Onuf’s nucleus) travel through the pudendal nerve to the external sphincter and the pelvic floor muscles. Somatosensory fibers from the bladder travel along the hypogastric and pelvic nerves to spinal levels T10–L2 and S2–S4, conveying information about the state of bladder stretch (overdistention is painful). The central nervous system (frontal lobes, basal ganglia) subserves the voluntary inhibition of detrusor contraction. The pontine micturition center, which triggers the act of micturition, is under the influence of afferent impulses relating to the state of bladder stretch; its output passes to somatic motor neurons in the spinal cord that synergistically innervate the detrusor and external sphincter muscles.

Continence. An intact bladder closure mechanism is essential for normal filling (up to 500 ml). Closure involves contraction of the vesical neck and external sphincter urethrae and pelvic floor muscles, and relaxation of the detrusor muscle (dome of the bladder).

Micturition. Once a urine volume of 150–250 ml has accumulated, stretch receptors generate impulses that pass to the pontine micturition center and also produce the sensation of bladder distention. Micturition begins when the dome of the bladder is stimulated to contract while the vesical neck and pelvic floor muscles relax. Contraction of the muscles of the abdominal wall increases the intravesical pressure and facilitates micturition.

Useful diagnostic aids include laboratory testing (urinalysis and renal function), ultrasound examination (kidney, bladder, pelvis), urodynamic testing, micturition cystourethrography, and neurophysiological studies (evoked potentials, urethroanal/bulbocavernosus reflex).

Sexual Function

The genital organs receive sympathetic (T11– L2), parasympathetic (S2–S4), somatic motor (Onuf’s nucleus), and somatosensory innervation (S2–S4) and are under supraspinal control, mostly through hypothalamic projections to the spinal cord. Hormonal factors also play an important role (p. 142). Neurological disease often causes sexual dysfunction (erectile dysfunction, ejaculatory dysfunction) in combination with bladder dysfunction. Isolated sexual dysfunction is more often due to psychological factors (depression, anxiety), diabetes mellitus, endocrine disorders, and atherosclerosis.

Sensory pathway

Pyramidal tract

Motor efferent fibers (pudendal n.)

External anal sphincter m.

Neural control of urinary bladder

(EUSM = external urethral sphincter m.)

Onuf’s nucleus

Spinal reflex arc

(sacral micturition center)

Inferior mesenteric ganglion

Urinary bladder (dome, detrusor muscle)

Internal urethral sphincter m.

EUSM

Streaky hemorrhage

Mild disk elevation (0.5 diopters), illdefined margins

Early papilledema

Elevated (3-5

Headache diopters) and enlarged disk with

irregular margins

Infarcts (cotton-wool spots)

Dilated vein

Papilledema

(fully developed)

Nausea

Herniation

(decerebration syndrome)

Herniation syndromes (p. 162). Transtentorial herniation causesanipsilateraloculomotornerve palsy (ptosis, mydriasis, and secondary ophthalmoplegia), contralateral hemiplegia, and decerebration syndrome (p. 46). Downward herniation ofthecontentsoftheposteriorfossaintotheforamen magnum causes neck pain and stiffness, a head tilt, and shoulder paresthesiae. If medullary compression is also present, respiratory and circulatorydisorders,cerebellarfits,andobstructivehydrocephalusmaydevelop. Upwardherniation of the contents of the posterior fossa across the tentorial notch causes a decerebration syndrome in which the ipsilateral pupil is initially constricted and later dilated.

Pseudotumor cerebri causes headache (holocephalic, bilateral frontal/occipital), visual disturbances of varying severity (enlarged blind spot, blurred vision, loss of vision, or diplopia due to abducens palsy), and bilateral papilledema. CT and MRI scans reveal the absence of an intracranialmass(normalventricularsize,thickening of optic nerve, “empty sella” = intrasellar expansion of the suprasellar cisterns, with or without sellar dilatation). CSF tests are normal except for an elevated opening pressure (!250 mmH2O). The etiology of pseudotumor cerebri is multifactorial; it occurs most commonly in obese young women. Its differential diagnosis includes intracranial venous or venous sinus thrombosis, drug toxicity (high doses of vitamin A, tetracycline, NSAIDs), elevated CSF protein level (spinal tumor, Guillain–Barré syndrome), or endocrine changes (pregnancy, Addison disease, Cushing syndrome, hypothyroidism).

Intracranial Hypotension

Spontaneous drainage of cerebrospinal fluid by means of lumbar puncture is no longer possible when the CSF pressure is below 20 mmH2O (patient is lying flat); when it is below 0 mmH2O, air is sucked through the LP needle into the subarachnoid space and travels upward to the head, where air bubbles can be seen on a CT scan. For causes of low intracranial pressure see Table 22 (p. 372).

! Symptoms

Severe headache (nuchal, occipital, or frontal) is provoked by sitting, standing, or walking, and

subsides when the patient lies flat. It is exacerbated by abdominal straining, coughing, and the Valsalva maneuver. Other symptoms include nausea, vomiting, and dizziness. Unilateral or bilateral abducens palsy, tinnitus, ear pressure, or neck stiffness may also occur. Subdural fluid collections (hematoma due to rupture of the bridging veins, hygroma arising from local CSF collection due to rupture of the arachnoid membrane) are rare. Intracranial hypotension may be caused by a CSF leak; patients may report occasional loss of watery fluid from the nose or ear (traces visible on pillows).

Normal-pressure hydrocephalus (NPH) is a chronic form of communicating hydrocephalus that reflects an impairment of CSF circulation and resorption, sometimes in the aftermath of subarachnoid hemorrhage, head trauma, or chronic meningitis, but often without discernible cause. Symptoms develop over several weeks or months. Gait disturbances (gait apraxia, hydrocephalic astasia-abasia) begin as unsteadiness, difficulty climbing stairs, leg fatigue, a small-stepped gait, and frequent stumbling and falling, and then typically progress to an inability to stand, sit, or turn over in bed. The associated behavioral changes (p. 132ff) are variable and may include impaired spatial orientation, reduced psychomotor drive (abulia), mild memory disturbances, or even dementia. Bladder dysfunction such as urge incontinence and polyuria develop as the condition progresses. Patients ultimately lose the perception of bladder distension and thus void uncontrollably.

Pathogenesis

ICP depends on the volume of nervous tissue, CSF, and blood inside the nondistensible cavity formed by the skull and vertebral canal. An increase in the volume of one of these three components must be offset by a compensatory mechanism (Monro–Kellie doctrine) such as an adjustment of the CSF or (venous) blood volume, expansion or the lumbosacral dural sheath, or deformation of the brain. When the capacity of such mechanisms is exhausted, the ICP decompensates. Compliance is defined as the first derivative of volume as a function of ICP, i.e., the ratio of a small, incremental change in