Background Accumulation of contrast medium in the subdural space after diagnostic intraarterial and intravenous contrast administrations is a rare observation. The authors report the case of a subdural contrast effusion (SCE) mimicking an acute subdural hematoma (SDH) presenting during embolization of an intracranial dural arteriovenous fistula (DAVF).

Clinical history A 52-year-old woman was admitted to our department with a four months history of left-sided numbness of the upper lip, cheek, tongue and forehead. Digital subtraction angiography showed a right tentorial DAVF with a venous ectasia. The DAVF was mainly supplied by the right middle meningeal artery, occipital artery and the artery of Bernasconi-Cassinari and drained into the Galenic venous system.

Procedure The patient underwent endovascular treatment with triaxial catheterization of the right occipital artery. Transarterial embolization using PHIL was performed and monitored by control runs made with an intermediate (distal access) catheter. After several injections, increased accumulation of contrast medium along the cerebellar tentorium and the walls of both transverse sinuses was noted. An immediately performed Dyna CT showed extensive contrast medium in the subdural space of the posterior cranial fossa and foramen magnum suspicious for an acute SDH. The catheters were removed, and the procedure was terminated. The patient woke up presenting no new symptoms and had an uneventful postoperative course. A 24-hour follow-up Dyna CT was completely normal suggesting the diagnosis of an asymptomatic SCE. We believe that repeat high pressure contrast injections via a large bore intermediate catheter into the territory of a (even partly) occluded DAVF may have induced leakage of contrast medium into the extravascular subdural space thereby causing a SCE.

Summary In conclusion we present the unique case of an asymptomatic SCE, which developed during transarterial embolization of a DAVF. SCE can occur during endovascular therapy and may mimic an acute SDH. Differentiation between the two by computed tomography or Dyna CT and early neurological examination can be crucial for patient management.

Disclosures R. Dahl: None. V. Eskesen: None. G. Benndorf: None.