What is the role of imaging studies in the workup of Haemophilus influenzae type b (Hib) meningitis?

Updated: Jul 09, 2018
  • Author: Prateek Lohia, MD, MHA; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Brain imaging studies may be of importance in patients with Hib meningitis. These studies are appropriately obtained in the acute setting to identify mass lesions that are in the differential diagnosis (eg, focal encephalitis, brain abscess, empyema, parasitism, subdural hemorrhages) not only for diagnostic purposes, but also to evaluate possible risks of lumbar puncture. Hence, evidence of focal neurologic dysfunction (ie, seizures, focal neurologic deficits) or of papilledema should prompt consideration of scanning.

Other indications for scanning during the initial or subsequent phases of hospitalization include persistently depressed or unexplained deterioration in neurologic status and prolonged fever despite treatment.

Scanning should never be performed before other critical management decisions have been made and acted instituted. If lumbar puncture is deferred until after scanning, adequate IV access must be established, blood cultures must be drawn, and broad-spectrum antibiotic coverage pertinent to any suspected meningitic agent should be administered.

If a scan is ordered because of seizures, full IV loading with an anticonvulsant should be considered. The authors regard phenobarbital as the drug of choice for this in young children because its sedative properties may make other forms of sedation unnecessary.

The wide therapeutic window of phenobarbital permits multiple additional doses to be administered if seizures are resistant to treatment, and this agent is easier to manage than phenytoin because of the nonlinear kinetics of phenytoin, if an anticonvulsant is judged necessary at discharge. Phenobarbital may also have beneficial effects in cases of increased ICP by reducing irritability and cerebral metabolic demand.

Brain imaging studies obtained at presentation are usually justified to identify an alternative diagnosis to meningitis (eg, brain abscess, subdural empyema) that may contraindicate a lumbar puncture. Results of imaging studies do not confirm the diagnosis of meningitis, which can only truly be confirmed by the performance of lumbar puncture. In instances where lumbar puncture is contraindicated, the presumption of meningitis may be made when the imaging results or clinical circumstances and other testing do not disclose an alternative diagnosis.

Go to Imaging in Bacterial Meningitis for more complete information on this topic.

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