How are subdural effusions diagnosed and managed in 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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Subdural effusions are common in Hib meningitis and are usually the result of an inflammation-induced increase in the permeability of capillaries and veins of the inner dural surface, permitting leakage of sterile fluid into the subdural space.

On CT imaging, subdural effusions are crescentic extra-axial collections between the outer surface of the brain and the inner surface of the skull, and their density is quite low, appearing similar to CSF. They are often bilateral and, if large, may flatten the anterior portions of the brain and may displace the frontal horns posteriorly. To some extent, the displacement posteriorly may be the artificial result of the recumbent positioning of the patient in the scanner. They do not usually enhance after contrast administration.

Subdural effusions are generally benign and do not cause symptoms and should in general be left alone. Eventually they resorb spontaneously, as the meningitis resolves. On occasion, however, subdural effusions can create local mass effect with involvement of local tissue. They may even result in elevated ICP, herniation, or focal signs. The development of new or progressive deficits, such as hemiparesis, during the course of illness may indicate that a subdural effusion has begun to exert mass effects.

Subdural effusions may become infected. On brain imaging, infection is suggested by the fact that the purulent material within the effusion produces an imaging appearance that is of higher density than CSF. IV contrast administration results in enhancement, especially at the border between cortex and subdural surface.

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