Fatal Cerebral Herniation After Lumbar Puncture in a Patient With a Normal Computed Tomography Scan

DISCUSSION

A cranial CT scan is often performed before LP in a comatose child suspected to have meningitis whenever significant concern of raised ICP exists. It is recommended that LP should be delayed if signs of increased ICP (eg, retinal changes, altered pupillary responses, increase in blood pressure with slow pulse rate, abnormal CT scan, or magnetic resonance imaging) are present.^9–11 Raised ICP is common in children with uncomplicated acute bacterial meningitis. Minns et al¹ found that 33 of 35 infants and children with pyogenic meningitis had a significant elevation in CSF pressure at the time of admission, but none had coning after LP and there were no deaths. Possible explanations for raised ICP in pyogenic meningitis include occlusion of arachnoid granulations, generalized inflammatory brain edema, basal occlusion of the subarachnoid spaces with development of hydrocephalus, status epilepticus, and syndrome of inappropriate antidiuretic hormone secretion.¹

Herniation or coning of the brain, the result of markedly raised ICP is a common postmortem finding in acute bacterial meningitis²and may be the direct cause of death in up to 30% of such children.¹² Symptoms and signs of herniation occur in about 5% of cases of bacterial meningitis.^{3 ,4} Herniation can occur at two sites: the cerebellar tonsils may protrude through the foramen magnum or the mesial temporal lobes may be forced downward through the tentorial opening. Although each may occur alone, tentorial herniation usually precedes foramen magnum herniation. The clinical diagnosis of cerebral herniation is usually relatively straightforward and typically has a rapid onset and proceeds in a rostral-caudal direction. There is progressive diminution in the level of consciousness, pupillary abnormalities, which may be unilateral or bilateral, in association with loss of oculocephalic responses or fixed oculomotor deviation of the eyes, tone abnormalities manifested by decorticate or decerebrate posturing, and respiratory abnormalities progressing through Cheyne-Stokes breathing, hyperventilation, ataxic breathing, followed by respiratory arrest. Unilateral herniation of one temporal lobe through the tentorial opening typically caused ipsilateral fixed dilated pupil and contralateral hemiparesis.^{13 ,14}

Early symptoms and signs of herniation may mimic the clinical picture of uncomplicated meningitis. Most children with bacterial meningitis are drowsy but rapid onset and progression to deep coma (Glasgow Coma Score <8) suggests raised ICP and LP is contraindicated.⁵Tonsillar herniation attributable to raised ICP may lead to neck stiffness, which may be confused with meningism attributable to meningitis or subaracnoid hemorrhage. When seizures occur it is difficult to differentiate the signs of herniation from the postictal state.^{2 ,4} The pupils may be dilated or unequal during or immediately after a seizure,¹⁵ and absent oculocephalic reflexes can be transiently suppressed.¹⁴ Some authors have suggested that a prolonged persistence of pupillary dilatation and, more important, absence of reaction to light indicate the probability of herniation rather than postictal state in cases of meningitis.⁴ Although convulsive seizures are not uncommon in early stages of meningitis and do not in themselves signify raised ICP, any seizures with accompanying hypoxia and hypercapnia may transiently elevate ICP in patients with meningitis.¹According to some experts, LP should not be done within 30 minutes after a short convulsive seizure or not at all after a prolonged convulsion.¹⁶ On the other hand, tonic seizures may be a symptom of high ICP and LP is contraindicated.¹⁷Papilledema is an uncommon finding in acute bacterial meningitis, even in the presence of markedly elevated ICP because it requires a minimum of 24 to 48 hours for the optic discs to become swollen,^{14 ,18} but its presence remains an absolute contraindication to LP.¹⁶

Several series have suggested that cerebral herniation typically occurs within 8 hours after hospital admission.^{3 ,4 ,19} Diagnostic LP may precipitate transtentorial or cerebellar herniation in some patients with meningitis.^3–5 In such cases, the interval from time of hospital admission to herniation may be within 30 minutes, suggesting that LP may have been the cause.⁴Dodge and Swartz³ found that herniation occurred within 2 hours of LP in 3 out of 9 cases diagnosed at postmortem examination. In their retrospective review, Rennick et al found that 8 (38%) of the 21 episodes of cerebral herniation occurred within 3 hours of LP and 12 (57%) occurred within 12 hours of LP; 6 (29%) of the 21 episodes of herniation occurred before LP or in a child who did not undergo LP.⁵ One report indicates that an LP may be responsible for up to 30% of deaths in the acute stages of meningitis.¹² Although herniation has been described in autopsies of children who died without an LP, most cases are identified in a hospital after an LP in children with meningitis who also have symptoms and signs consistent with cerebral herniation.^2–5 Delaying LP in such instances may be lifesaving.

The ease and relative safety of CT scanning make it an initial diagnostic procedure of choice when evaluating mass lesions and/or the possibility of increased ICP. Unfortunately, in most cases the results of CT scan are normal in acute meningitis at presentation.^{18 ,20 ,21} Cerebral edema may produce CT abnormalities including slitlike lateral and third ventricles, generalized low attenuation of the white matter, and obliteration of the basilar and suprachiasmatic cisterns.²¹ However, there is considerable variation in ventricular and cisternal size making interpretation of a single scan unreliable. In a prospective study of bacterial meningitis, CT findings obtained during the acute stages failed to reveal any clinically significant abnormalities that were not suspected on neurologic examination.²² On the other hand CT is very beneficial in excluding those conditions that may mimic bacterial meningitis with raised ICP. These conditions include posterior fossa tumors, acute hydrocephalus, cerebral abscess, and intracranial bleeds, all which are readily diagnosed by CT.

The present case with meningitis and progressive loss of consciousness after a seizure should have raised the suspicion of raised ICP. An LP then precipitated the brain herniation, and the initial CT failed to predict imminent herniation. Rennick et al⁵ reported a 15-year-old adolescent with bacterial meningitis with a normal CT scan who developed herniation confirmed at postmortem examination within 30 minutes of a diagnostic LP. The present report is the second documented case of herniation subsequent to a diagnostic spinal tap in a child with a normal CT scan. It clearly illustrates the fact that normal results on CT do not mean that it is safe to do an LP in a patient with bacterial meningitis. When the child's condition has stabilized, a decision can be made as to the need for an LP. This case also brings to light the importance of measuring the OP at the time of diagnostic LP. Careful measurement of OP by relieving neck and hip flexion can identify markedly elevated ICP that would allow prompt treatment with osmotic agent such as mannitol and hyperventilation to prevent herniation and avoid potentially fatal outcome.¹¹When the OP is very high, just enough fluid (usually 2 to 4 mL) should be removed to permit a careful examination.^{10 ,11}The use of a small bore needle (21- or 22-gauge) is recommended whenever there is concern about increased ICP to minimize the CSF leak from the LP site.¹¹

Fortunately, a vast majority of children presenting with suspected bacterial meningitis have no clinical evidence of herniation. A routine CT scan of the brain is not indicated in such cases.¹⁸ A diagnostic LP should be done expeditiously and appropriate antibiotic therapy should be promptly initiated. A CT scan should be performed before LP for patients with clinical evidence of raised ICP such as marked obtundation (Glasgow Coma Scale <8), prolonged/tonic seizures, focal neurologic signs, abnormalities in posture and respiratory pattern, pupillary changes, absent oculocephalic reflexes, or papilledema.