Case 27
History:
65 year old male with progressive intellectual deterioration and gait difficulty undergoing a "dementia work-up"
Findings:
Our patient (Patient A) first had a brain MRI showing dilatation of ventricular system out of proportion to the degree of atrophy. Also notice the flow void at the aquaduct of sylvius on the sagittal T1 weighted images (white arrow) see corresponding diagram. A radionuclide cisternogram demonstrated trace in the lateral ventricles at 4hours and persisting on delayed scans (not shown). Contrast with a normal subject (Patient B) showing the characteristic Neptune's triumviratea or trident appearance reflecting ascending radionuclide into the interhemispheric and Sylvian fissures (arrows).
Diagnosis:
Normal pressure hydrocephalus (NPH)
Discussion:
Normal pressure hydrocephalus (NPH) is one of the few treatable causes of dementia. The typical clinical triad consists of gait disturbance (often described as magnetic gait), dementia or difficulty with memory, and incontinence in a patient communicating hydrocephalus. The response to shunting seems to be less successful (30–50%) in patients with the idiopathic form than for patients with a known cause of communicating hydrocephalus (50–70%). Some of the etiologies to communicating hydrocephalus include: prior subarachnoid hemorrhage, meningitis or other inflammatory process, neurosurgical intervention, and prior traumatic injury. The gait disturbance is often the first symptom to appear and to improve following VP shunting, probably due to the fact that the corticospinal tract fibers supplying the motor function to the lower extremities are at very close proximity to the lateral ventricles within the corona radiata. Several diagnostic tests have been used to determine which patients might benefit from VP shunting. Although they can be complementary, no one test really emerged from the group.
Cisternography is performed by introducing Indium-111-DTPA intrathecally via a lumbar puncture. Images are typically acquired at 6, 24 and 48 hours. In normal subjects, the tracer will rise to the basal cisterns in 1 to 3 hours, giving the “Neptune’s triumvirate” or “trident” appearance reflecting radiotrace in the interhemispheric and Sylvian fissures The tracer will then proceed to flow over the convexities collecting in the sagittal area in 12 to 24 hours. The lateral ventricles are normally not visualized. A small amount of activity in the lateral ventricles within the first 24 hours can be seen in a small percent of normal subjects and is generally disregarded. Persistent activity within the lateral ventricles after 24 hours is virtually diagnostic in the proper clinical setting.
In patients with normal pressure hydrocephalus, there usually is ventricular “reflux” of the radiotracer, which persists for 24-48 hours or more. Little or no activity is seen over the cerebral convexities. This test is helpful when positive but of little value if negative.
MRI examination typically show communicating hydrocephalus with the ventricular system dilated out of proportion to the degree of volume loss distinguishing it from the usual age related volume loss. Ill defined often bilateral periventricular hallo of T2 hyperintensity signal can be seen representing subependymal CSF resorption. Also a prominent aquaductal flow void may be encountered especially with conventional spin echo proton density–weighted technique.
References:
- William G. Bradley. Normal Pressure Hydrocephalus: New Concepts on Etiology and Diagnosis. American Journal of Neuroradiology 21:1586-1590 (10 2000)
- Benzel E, Pelletier A, Levy P. Communicating Hydrocephalus in Adults: Prediction of Outcome after Ventricular Shunting Procedures. Neurosurgery 26:655-660,1990.
- Benson D, LeMay M, Patten D, Rubens A. Diagnosis of normal pressure hydrocephalus. New Eng J Med 1970;283:609-615.
- Sandler PM, et al. Diagnostic Nuclear Medicine, 3rd edition, 1996. Williams and Wilkins.
- Datz, et al. Nuclear Medicine: a teaching file. 1992. Mosby Yearbook
