Niedrigdosis-Schädel-CT zur Beurteilung der Ventrikelweite (und darüber hinaus)

Whole-body ultra-low-dose CT (ULD-CT) has replaced radiographic shunt series as the standard imaging method for CSF shunts at our institution. However, ULD-CT has limitations in assessing intracranial structures, and full-dose cranial CT (cCT) remains the standard for evaluating ventricular width and hygroma/subdural hematoma as potential signs of overdrainage. Patients with implanted CSF shunts often undergo multiple cCT scans, leading to high radiation exposure. Therefore, we developed a novel low-dose (LD) protocol primarily for evaluating ventricular width and retrospectively analyzed its feasibility.

Eighty-two cranial LD-CTs (100kV, 60mAs) were performed at our institution between January 15th 2021, and January 14th 2022. The DLP (dose length product) and calculated effective dose of LD-CTs were assessed and compared with full-dose CTs. Clinical performance, including therapeutic consequences, was also evaluated.

The average age was 51 years (+/-19), with 46% being female. The most common diagnosis was post-hemorrhagic hydrocephalus (24%), followed by tumor-associated and congenital hydrocephalus. LD-CT was performed in an outpatient setting for 69%, 9% through the emergency department, and 22% in the inpatient setting. 85% of patients had a VP shunt, 3% a VA shunt, and 12% had no shunt (including monitoring for subdural/epidural effusions, pneumocephalus, or CSF cushions). In 17% of cases, hygromas/SDH were diagnosed as signs of overdrainage or primary pathology.

When compared with the pre-cCT examination, ventricular width was significantly regressed in 8%, slightly regressed in 21%, remained the same in 58%, slightly progressed in 8%, and significantly progressed in 4%. The valve pressure level was reduced in 18%, maintained in 41%, and increased in 10%. Surgical therapy was performed in 11% of cases, early follow-up in 16%, and other measures in 4%. Additional imaging (one cCT and one cMRT) was necessary for surgical planning in only 2 cases.

The median CT dose index of LD-CTs was 5.93 mGy, and the median DLP for the cranium was 77 mGy*cm (which corresponds to an effective dose of 0.16 mSv), reaching 9.5% of the radiation dose of standard cCT (median DLP: 808 mGy*cm).

LD-CT allows for accurate evaluation of ventricular width, sulcal relief, and subdural hygroma. This may be particularly relevant in younger patients. Further studies are needed to determine the optimal low-dose protocol for assessing subdural hematoma.