RESUMO
BACKGROUND: Infundibula are frequently regarded as incidental anatomical variants that are of no pathogenetic significance. CASE DESCRIPTION: A 51-year-old man presented with a sudden onset of severe occipital headache. Computed tomographic scan revealed a predominantly perimesencephalic pattern of SAH with a slight bias toward the left side. Angiography demonstrated a left PCo-A IF as the sole abnormality. At craniotomy, the left PCo-A IF was found to represent the sole abnormality. The IF was markedly reddened posteriorly, contained a capping clot, and lay immediately adjacent to a mass of xanthochromatous tissue. The PCo-A was hypoplastic and lacked perforating vessels; therefore, the IF base was successfully clipped with a straight Sugita clip parallel to the left ICA. At discharge and at clinical follow-up, our patient was asymptomatic and lacked neurologic signs. CONCLUSIONS: Infundibula may rarely represent a direct source of rupture and SAH. Exploratory craniotomy is required to establish the diagnosis and to provide definitive treatment. To label a case of SAH as angiogram-negative may be unwise when an IF potentially colocalizes to the SAH source.