A 68 year old woman with a known glioblastoma multiforme presented with approximately one week of confusion and drowsiness. Examination showed word-finding difficulties, right homonymous hemianopsia and right arm apraxia. The left pupil was larger on the right and poorly reactive.
 

 

Axial T1-weighted images with gadolinium. The patient's MRI shows midline shift and herniation. Note the displacement of the medial temporal lobe (uncus) against the midbrain. In addition, note that the ambien cistern is asymmetric and larger on the left. This occurs from the brainstem being torqued from above. The presence of an awake individual with such massive shift of brain structures implies that the displacement of brain structures occurred relatively slowly, allowing time for metabolic compensation. In a patient where this process occurs quickly, such as an acute subdural hematoma, this degree of herniation is often associated with depressed consciousness or coma.

This displacement of brain strucutres illustrates the Monro-Kellie doctrine: i.e. in an adult the cranial volume is a constant. The cranial contents consist prinicipally of brain, cerebrospinal fluid and blood vessels. These compartments must shift to accomodate new masses such as hematomas, tumors or edema fluid. In a patient with loss of brain mass, such as occurs after a stroke or neurosurgery, the CSF spaces often enlarge to fill the void.

Revised 04/20/06.
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