Variations in the morphology of lagomorph confluence sinuum on contrast enhanced CT

Kelsey Jorge, Sara Tolliver, David Gasper, Christoph Mans, Seng Wai Yap

Background: The cerebral dural venous sinus system is a network of veins that drains blood from the brain and cranium. The confluence sinuum is a triangular structure that receives blood from the dorsal sagittal sinus, straight sinus, and ventromedial and ventrolateral veins. The morphology of the confluence sinuum in rabbits on contrast-enhanced CT has not been well described.

Study: The authors performed a retrospective, observational, and descriptive study to describe the characteristics of the confluence sinuum in rabbits on contrast-enhanced CT and to compare the degree of contrast enhancement and Hounsfield units (HU) among different groups.

Methods: Images of 24 rabbits who had pre- and postcontrast CT sequences of the skull were reviewed by a radiologist and a radiology resident. The degree of contrast enhancement within the region of the confluence sinuum was graded as mild, moderate, or marked. HU of the confluence sinuum was measured in three different regions of interest and averaged for each patient. One-way ANOVA analysis was used to compare the mean HU among the groups.

Results: Contrast enhancement was identified in all rabbits (24/24) on contrast-enhanced CT imaging. Contrast enhancement was mild in 45.8% (11/24) rabbits, moderate in 33.3% (8/24), and marked in 20.8% (5/24). There were significant differences (P < 0.05) between the average HU of the mild and marked group and the moderate and marked groups. Two rabbits with marked contrast enhancement were initially misdiagnosed with an intracranial, extra-axial mass based on contrast-enhanced CT, but necropsy confirmed normal brain parenchyma.

Limitations: The study had a small sample size and did not account for confounding factors such as patient size, time of postcontrast sequences, heart rate, and beam hardening artifact. The time of injection of contrast material to the start of the postcontrast sequence acquisition was not recorded or standardized. Only four rabbits had necropsies performed to confirm the absence of intracranial abnormalities.

Conclusions: The study described the variable features of the normal confluence sinuum and straight sinus in rabbits on contrast-enhanced CT. The confluence sinuum can be variable in size and shape and should not be mistaken for a pathological lesion in the absence of mass effect or secondary calvarial changes. Recognition of the normal lagomorph cerebral venous system and its variation in size is clinically important to prevent misdiagnoses.

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