Nervous System Disorders

Published on 27/03/2015 by admin

Last modified 27/03/2015

Print this page

This article have been viewed 2642 times

Chapter 93 Nervous System Disorders

Central nervous system (CNS) disorders are important causes of neonatal mortality and both short- and long-term morbidity. The CNS can be damaged as a result of hypoxia, asphyxia, hemorrhage, trauma, hypoglycemia, or direct cytotoxicity. The etiology of CNS damage is often multifactorial and includes acute perinatal complications, postnatal hemodynamic instability, and developmental abnormalities that may be genetic and/or environmental. Predisposing factors for brain injury include chronic and acute maternal illness resulting in uteroplacental dysfunction, intrauterine infection, macrosomia/dystocia, malpresentation, prematurity, and intrauterine growth restriction. Acute and often unavoidable emergencies during the delivery process frequently result in mechanical and/or hypoxic-ischemic brain injury.

93.1 The Cranium

Waldemar A. Carlo

Erythema, abrasions, ecchymoses, and subcutaneous fat necrosis of facial or scalp soft tissues may be noted after a normal delivery or after forceps or vacuum-assisted deliveries. Their location depends on the area of contact with the pelvic bones or of application of the forceps. Traumatic hemorrhage may involve any layer of the scalp as well as intracranial contents (Fig. 93-1).

Figure 93-1 Sites of extracranial (and extradural) hemorrhages in the newborn. Schematic diagram of important tissue planes from skin to dura.

(From Volpe JJ: Neurology of the newborn, ed 4, Philadelphia, 2001, WB Saunders.)

Caput succedaneum is a diffuse, sometimes ecchymotic, edematous swelling of the soft tissues of the scalp involving the area presenting during vertex delivery (see Fig. 93-1). It may extend across the midline and across suture lines. The edema disappears within the 1st few days of life. Molding of the head and overriding of the parietal bones are frequently associated with caput succedaneum and become more evident after the caput has receded; they disappear during the 1st weeks of life. Rarely, a hemorrhagic caput may result in shock and require blood transfusion. Analogous swelling, discoloration, and distortion of the face are seen in face presentations. No specific treatment is needed, but if extensive ecchymoses are present, hyperbilirubinemia may develop.

Cephalohematoma (Fig. 93-2) is a subperiosteal hemorrhage, hence always limited to the surface of one cranial bone. Cephalohematomas occur in 1-2% of live births. No discoloration of the overlying scalp occurs, and swelling is not usually visible for several hours after birth because subperiosteal bleeding is a slow process. The lesion becomes a firm tense mass with a palpable rim localized over one area of the skull. Most cephalohematomas are resorbed within 2 wk-3 mo, depending on their size. They may begin to calcify by the end of the 2nd week. A few remain for years as bony protuberances and are detectable on radiographs as widening of the diploic space; cystlike defects may persist for months or years. An underlying skull fracture, usually linear and not depressed, may be associated with 10-25% of cases. A sensation of central depression suggesting but not indicative of an underlying fracture or bony defect is usually encountered on palpation of the organized rim of a cephalohematoma. Cephalohematomas require no treatment, although phototherapy may be necessary to treat hyperbilirubinemia. Infection of the hematoma is a very rare complication.

Figure 93-2 Cephalohematoma of the right parietal bone.

A subgaleal hemorrhage is a collection of blood beneath the aponeurosis that covers the scalp the entire length of the occipitofrontalis muscle. Bleeding can be very extensive into this large potential space and may even dissect into the subcutaneous tissues of the neck. There is often an association with vacuum-assisted delivery. The mechanism of injury is most likely secondary to a linear skull fracture, suture diastasis or fragmentation of the superior margin of the parietal bone, and/or rupture of the emissary vein. Extensive subgaleal bleeding is occasionally secondary to a hereditary coagulopathy (hemophilia). A subgaleal hemorrhage manifests as a firm fluctuant mass that increases in size after birth. Many patients have a consumptive coagulopathy owing to massive blood loss. Patients should be monitored for hypotension and the development of hyperbilirubinemia. These lesions typically resolve over 2-3 weeks.

Fractures of the skull may occur as a result of pressure from forceps or from the maternal symphysis pubis, sacral promontory, or ischial spines. Linear fractures, the most common, cause no symptoms and require no treatment. Depressed fractures are usually indentations of the calvaria similar to the dents in a ping-pong ball; they are generally a complication of forceps delivery or fetal compression. Affected infants may be asymptomatic unless they have associated intracranial injury; it is advisable to elevate severe depressions to prevent cortical injury from sustained pressure. Fracture of the occipital bone with separation of the basal and squamous portions almost invariably causes fatal hemorrhage because of disruption of the underlying vascular sinuses. Such fractures may result during breech deliveries from traction on the hyperextended spine of the infant while the head is fixed in the maternal pelvis.

Subconjunctival and retinal hemorrhages are frequent; petechiae of the skin of the head and neck are also common. All are probably secondary to a sudden increase in intrathoracic pressure during passage of the chest through the birth canal. Parents should be assured that these hemorrhages are temporary and the result of normal events of delivery. The lesions resolve rapidly within the 1st 2 wk of life.

93.2 Traumatic, Epidural, Subdural, and Subarachnoid Hemorrhage

Waldemar A. Carlo

Traumatic epidural, subdural, or subarachnoid hemorrhage is especially likely when the fetal head is large in proportion to the size of the mother’s pelvic outlet, with prolonged labor, in breech or precipitous deliveries, or as a result of mechanical assistance with delivery. Massive subdural hemorrhage, often associated with tears in the tentorium cerebelli or, less frequently, in the falx cerebri, is rare but is encountered more often in full-term than in premature infants. Patients with massive hemorrhage caused by tears of the tentorium or falx cerebri rapidly deteriorate and may die soon after birth. The majority of subdural and epidural hemorrhages resolve without intervention; consultation with a neurosurgeon is recommended. The diagnosis of subdural hemorrhage may be delayed until the chronic subdural fluid volume expands and produces megalocephaly, frontal bossing, a bulging fontanel, anemia, and, sometimes, seizures. CT scan and MRI are useful imaging techniques to confirm these diagnoses. Symptomatic subdural hemorrhage in large term infants should be treated by removal of the subdural fluid collection with a needle placed through the lateral margin of the anterior fontanelle. In addition to birth trauma, child abuse must be suspected in all infants with subdural effusion after the immediate neonatal period.

Subarachnoid hemorrhage (SAH) is rare and typically is clinically silent. The anastomoses between the penetrating leptomeningeal arteries or the bridging veins are the most likely source of the bleeding. The majority of affected infants have no clinical symptoms, but the SAH may be detected because of an elevated number of red blood cells in a lumbar puncture sample. Some infants experience benign seizures, which tend to occur on the 2nd day of life. Rarely, an infant has a life-threatening catastrophic hemorrhage and dies. There are usually no neurologic abnormalities during the acute episode or on follow-up. Significant neurologic findings should suggest an arteriovenous malformation; this lesion can easily be detected on CT or MRI; ultrasonography is a less sensitive tool.

93.3 Intracranial-Intraventricular Hemorrhage and Periventricular Leukomalacia

Waldemar A. Carlo

Etiology

Intracranial hemorrhage usually develops spontaneously; less commonly, it may be due to trauma or asphyxia, and rarely, it occurs from a primary hemorrhagic disturbance or congenital vascular anomaly. Intracranial hemorrhage often involves the ventricles (intraventricular hemorrhage [IVH]) of premature infants delivered spontaneously without apparent trauma. Primary hemorrhagic disturbances and vascular malformations are rare and usually give rise to subarachnoid or intracerebral hemorrhage. In utero hemorrhage associated with maternal idiopathic or, more often, fetal alloimmune thrombocytopenia may occur as severe cerebral hemorrhage or a porencephalic cyst after resolution of a fetal cortical hemorrhage. Intracranial bleeding may be associated with disseminated intravascular coagulopathy, isoimmune thrombocytopenia, and neonatal vitamin K deficiency, especially in infants born to mothers receiving phenobarbital or phenytoin.

Epidemiology

The overall incidence of IVH has decreased over the past decades as a result of improved perinatal care and increased use of antenatal corticosteroids, surfactant to treat respiratory distress syndrome (RDS), and, possibly, prophylactic indomethacin; however, it continues to be an important cause of morbidity in preterm infants. Approximately 30% of premature infants <1,500 g have IVH. The risk is inversely related to gestational age and birthweight, with the smallest and most immature infants being at the highest risk; 7% of infants 1,001-1,500 g have a severe IVH (grade III or IV), compared with 14% of infants 751-1,000 g and 24% of infants ≤750 g. In 3% of infants <1,000 g, periventricular leukomalacia (PVL) develops.

Pathogenesis

The major neuropathologic lesions associated with VLBW infants are IVH and PVL. IVH in premature infants occurs in the gelatinous subependymal germinal matrix. This periventricular area is the site of origin for embryonal neurons and fetal glial cells, which migrate outwardly to the cortex. Immature blood vessels in this highly vascular region of the developing brain combined with poor tissue vascular support predispose premature infants to hemorrhage. The germinal matrix involutes as the infant approaches full-term gestation and the tissue’s vascular integrity improves; therefore IVH is much less common in the term infant. Periventricular hemorrhagic infarction often develops after a grade IV IVH owing to venous congestion. Predisposing factors for IVH include prematurity, respiratory distress syndrome, hypoxic-ischemic or hypotensive injury, reperfusion injury of damaged vessels, increased or decreased cerebral blood flow, reduced vascular integrity, increased venous pressure, pneumothorax, thrombocytopenia, hypervolemia, and hypertension.

Understanding of the pathogenesis of PVL is evolving, and it appears to involve both intrauterine and postnatal events. A complex interaction exists between the development of the cerebral vasculature and the regulation of cerebral blood flow (both of which are gestational age dependent), disturbances in the oligodendrocyte precursors required for myelination, and maternal/fetal infection and/or inflammation. Similar factors (hypoxia-ischemia), venous obstruction from an IVH, or undetected fetal stress may result in decreased perfusion to the brain, leading in turn to periventricular hemorrhage and necrosis. PVL is characterized by focal necrotic lesions in the periventricular white matter and/or more diffuse white matter damage. The risk for PVL increases in infants with severe IVH and/or ventriculomegaly. The corticospinal tracts descend through the periventricular white matter, hence the association between cerebral white matter injury/PVL and motor abnormalities, including cerebral palsy.

Clinical Manifestations

The majority of patients with IVH, including some with moderate to severe hemorrhages, have no clinical symptoms. Some premature infants in whom severe IVH develops may have acute deterioration on the 2nd or 3rd day of life. Hypotension, apnea, pallor, or cyanosis; poor suck; abnormal eye signs; a high-pitched, shrill cry; convulsions, or decreased muscle tone; metabolic acidosis; shock; and a decreased hematocrit or failure of the hematocrit to increase after transfusion may be the 1st clinical indications. IVH may rarely manifest at birth; 50% of cases are diagnosed within the 1st day of life, and up to 75% within the 1st 3 days. A small percentage of infants have late hemorrhage, between days 14 and 30. IVH as a primary event is rare after the 1st month of life.

PVL is usually clinically asymptomatic until the neurologic sequelae of white matter damage become apparent in later infancy as spastic motor deficits. PVL may be present at birth but usually occurs later as an early echodense phase (3-10 days of life), followed by the typical echolucent (cystic) phase (14-20 days of life).

The severity of hemorrhage may be defined on CT scans by the location and degree of ventricular dilatation. In a grade I hemorrhage, bleeding is isolated to the subependymal area. In Grade II hemorrhage, there is bleeding within the ventricle but without evidence of ventricular dilatation. Grade III hemorrhage consists of IVH with ventricular dilatation. In Grade IV hemorrhage, there is intraventricular and parenchymal hemorrhage. Another grading system describes 3 levels of increasing severity of IVH detected on ultrasound: In grade I, bleeding is confined to the germinal matrix–subependymal region or to <10% of the ventricle (≈35% of IVH cases); grade II is defined as intraventricular bleeding with 10-50% filling of the ventricle (≈40% of IVH cases) and in grade III, more than 50% of the ventricle is involved, with dilated ventricles (Fig. 93-3). Ventriculomegaly is defined as mild (0.5-1 cm), moderate (1.0-1.5 cm), or severe (>1.5 cm).

Figure 93-3 Grading the severity of germinal matrix intraventricular hemorrhage with parasagittal ultrasound scans. A, Grade I: Note the echogenic blood in the germinal matrix (arrowheads) just anterior to the anterior tip of the choroid plexus, which (normally) is also echogenic. B, Grade II: Note the echogenic blood (arrowheads) filling <50% of the ventricular area. C, Grade III: Note the large blood clot nearly completely filling and distending the entire lateral ventricle.

(From Intracranial hemorrhage: germinal matrix-intraventricular hemorrhage of the premature infant. In Volpe JJ: Neurology of the newborn, ed 4, Philadelphia, 2001, WB Saunders.)