Case Author(s): Gregg Schubach, M.D. and Keith Fischer, M.D. , 4/5/96 . Rating: #D3, #Q5

Diagnosis: Normal-pressure hydrocephalus

Brief history:

76-year old woman with mild dementia, ataxia, and urinary incontinence.

Images:

48 hr delayed cisternogram images

View main image(ci) in a separate image viewer

View second image(ct). Axial CT image at level of lateral ventricles

Full history/Diagnosis is available below

Diagnosis: Normal-pressure hydrocephalus

Full history:

This 76-year old woman with mild dementia, ataxia, and urinary incontinence was found to have ventriculomegaly on a recent CT study of the brain. This examination was performed to assess for possible normal-pressure hydrocephalus.

Radiopharmaceutical:

0.5 mCi In-111 DTPA

Findings:

The non-contrast enhanced CT study of the brain demonstrates ventriculomegaly and a left occipital infarct. The 24 and 48-hour delayed scintigraphic image in anterior and left lateral projections demonstrates activity within the lateral ventricles. There is also a paucity of activity along the outer convexity of the brain superiorly (near the vertex).

Discussion:

Radionuclide cisternography is performed using an intrathecal (subarachnoid) lumbar injection of In-111 DTPA. A 15-30 minute posterior image over the thoracolumbar spine is routinely obtained to document proper administration of the radiopharmaceutical into the subarachnoid space. Images of the head are obtained at 4, 24, and 48 hours in the anterior, left lateral, and posterior projections. In pediatric patients, however, images are generally obtained at 2, 12, and 24 hours because of more rapid cerebrospinal fluid flow. In-111 DTPA, which is diffusible in CSF, remains in the CSF space until it is absorbed through the arachnoid granulations near the superior sagittal sinus. The radiopharmaceutical is then cleared from the extracellular space by the kidneys via glomerular filtration. The physical half-life of In-111 is 67 hours. In-111 DTPA cisternography delivers 0.1 rad/mCi total body radiation, 2.3 rad/mCi to the brain, and 1.3 rad/mCi to the spinal cord.

The total volume of CSF is about 120 mL with about one-third of this within the ventricular system and two-thirds bathing the brain and spinal cord. CSF is formed by the choroid plexus in the lateral ventricles. Normal CSF flow is through the foramen of Monroe into the third ventricle, where it exists via the aqueduct of Sylvius to the fourth ventricle. CSF then exists the ventricular system via the foramen of Luschka and Magendie to enter the basal cisterns and subarachnoid space surrounding the brain.

Normal-pressure hydrocephalus is characterized by the classic triad of dementia, ataxia, and urinary incontinence. Although the etiology of normal- pressure hydrocephalus is unknown, it remains one of the few causes of treatable pre-senile dementia. It is thought to begin with an obstruction to CSF flow either in the ventricles or basal cisterns, with resultant ventriculomegaly. The CSF pressure then slowly returns to normal with persistently enlarged ventricles. While the clinical findings are classic, the CT findings are easily confused with atrophy.The pattern of CSF flow in patients with normal-pressure hydrocephalus is abnormal and can be assessed with radionuclide cisternography.

The normal radionuclide cisternogram demonstrates activity ascending to the basal cisterns by four hours. The radiopharmaceutical will extend into the interhemispheric and Sylvian fissures forming the so-called Neptune's triumvirate. Activity should be identified over the convexities of the brain by 24 hours. Normally, there is no reflux of activity into the lateral ventricles. However, a small amount of activity which is transiently present in the lateral ventricles within the first 24 hours is within the accepted limits of normal and generally disregarded. Persistent activity within the lateral ventricles after 24 hours is virtually diagnostic in the proper clinical setting.

Treatment includes shunting of CSF flow, such as with a ventriculoperitoneal shunt. While some patients respond dramatically to treatment, the CSF flow pattern on cisternography does not predict the patientıs response to ventricular shunting. Patients with chronic normal-pressure hydrocephalus typically respond less well than those patients with acute disease. Thus, clinical data, and not imaging, determines whether a patient is to be treated.

Radionuclide cisternography does not diagnose normal-pressure hydrocephalus, per se. Rather, it diagnoses obstructive, communicating hydrocephalus in patients with a clinical suspicion of normal- pressure hydrocephalus (classic clinical triad) with ventriculomegaly on CT scan (atrophy vs NPH). The other common indication for radionuclide cisternography is detection of a CSF leak.

References:

1) Sandler PM, et al. Diagnostic Nuclear Medicine, 3rd edition, 1996. Williams and Wilkins

2) Datz, et al. Nuclear Medicine: a teaching file. 1992. Mosby Yearbook

Differential Diagnosis List

The differential diagnosis includes obstructive communicating hydrocephalus attributed to other etiologies, such as meningitis or prior subarachnoid hemorrhage.

ACR Codes and Keywords:

References and General Discussion of Cisternography (Anatomic field:Skull and Contents, Category:Organ specific)

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Case number: ci001

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