Prone Dynamic CT Myelography in Spontaneous Intracranial Hypotension : Diagnostic Need and Radiation Doses.

Abstract

The diagnostic work-up in patients with spontaneous intracranial hypotension (SIH) and spinal longitudinal extradural CSF collection (SLEC) on magnetic resonance imaging (MRI) comprises dynamic digital subtraction myelography (dDSM) in prone position for leak detection. Dynamic computed tomography (CT) myelography (dCT-M) in prone position follows if the leak is not unequivocally located. A drawback of dCT‑M is ahigh radiation dose. This study evaluates the diagnostic needs of dCT-M examinations and measures to reduce radiation doses. Frequency, leak sites, length and number of spiral acquisitions, DLP and effective doses of dCT‑M were retrospectively recorded in patients with ventral dural tears. Of 42patients with ventral dural tears, 8 underwent 11dCT‑M when the leak was not unequivocally shown on digital subtraction myelography. The median number of spiral acquisitions was 4 (range 3-7) and the mean effective radiation dose 30.6 mSv (range 13.1-62.16 mSv) mSv. Five of eight leaks were located in the upper thoracic spine (range C7/Th1-Th2/3). Bolus tracking of intrathecal contrast agent in dCT‑M was used to limit the number and length of spiral acquisitions. A dCT‑M in prone position to localize aventral dural tear is needed in every fifth patient with aSLEC on MRI. It is typically needed when the leak is located in the upper thoracic spine and when patients have broad shoulders. Measures to reduce the radiation dose include bolus tracking or to repeat the DSM with adjusted positioning of patient.