The "connecting vessel" sign: an imaging biomarker to differentiate ruptured infected (mycotic) intracranial aneurysm mimicking the CTA spot sign.

Purpose: Infected (mycotic) intracranial aneurysms (IIA) are a prevalent source of morbidity in patients with systemic infection. Unlike saccular aneurysms, ruptured IIA frequently presents with intracerebral hemorrhage (ICH), and the appearance of ruptured IIA on CTA overlaps with the CTA "Spot Sign" (SS), an imaging finding in non-infectious, spontaneous ICH. The purpose of this study was to investigate the imaging and clinical features which may differentiate these two entities on CTA for which treatment strategies differ substantially.

Methods: In an IRB-approved, retrospective case series, we compared 14 patients with confirmed IIA and 14 patients with positive SS due to other non-infectious etiology (SS(+) ICH). Clinical history, laboratory studies, and CTA reports and images were reviewed to define imaging characteristics of IIA and SS(+) ICH, including the diagnostic criteria for SS used in clinical trials.

Results: A total of 7/14 patients (50.0%) diagnosed with IIA had ICH at presentation. Of these, 3/7 patients (42.9%) with ruptured IIA and ICH met diagnostic imaging criteria of SS. The remaining 4/7 patients did not meet criteria due to presence of a connecting vessel. Compared with SS(+) ICH of non-infectious etiology, patients with ruptured IIA were younger (40.7 vs. 66.4 years) and had higher rates of IVDU and bacteremia (p < 0.01) and lower rates of hypertension (p < 0.01). Hematoma volume was similar in both groups, but lobar location was more frequent in ruptured IIA (p = 0.06). Mortality at 1 year from diagnosis was equally high in both groups (42.9%).

Conclusion: This study characterizes ruptured IIA as an imaging mimic of SS and provides a framework for differentiating these lesions, allowing prompt diagnosis and appropriate treatment.