Evaluation of a limited three-slice head CT protocol for monitoring patients with ventriculoperitoneal shunts

Patients with a ventriculoperitoneal shunt for the management of hydrocephalus often undergo multiple head CT examinations for assessment of shunt malfunction. The purpose of this study was to evaluate whether a limited three-slice CT protocol would consistently provide adequate information for the diagnosis of shunt malfunction with a decrease in effective dose.

The study group included 231 unenhanced head CT examinations performed on 128 patients with shunts for hydrocephalus. The original contiguous CT images were reviewed retrospectively. A theoretic limited three-slice study was then created from the original complete CT study and separately reviewed. This limited three-slice study was created by using the lateral topographic image to select three axial locations as follows: midpoint between foramen magnum and vertex, top of the mastoid air cells, and orbital roof. The limited study was graded for parameters of image adequacy with the original full protocol study as the reference standard.

Twenty-four of the 231 (10.4%) full studies had findings consistent with shunt failure; all 231 studies would have been correctly categorized with the limited three-slice protocol. The sensitivity of three-slice CT for identifying the ventricular system was 91.6% and for identifying the catheter tip, 93.5%. Limited-slice CT examination would have resulted in greater than 90% mean dose reduction in both adult and pediatric populations.

Unenhanced head CT with a limited-slice protocol provides adequate diagnostic information for the diagnosis of shunt malfunction with a greater than 90% reduction in effective dose.