2026 Poster Presentations
P111: GIANT ARACHNOID GRANULATIONS OF THE TRANSVERSE AND SIGMOID SINUSES: ANALYSIS OF MORPHOLOGY AND CLINICAL RELEVANCE IN 100 POSTERIOR FOSSA SURGERIES
Keisuke Murofushi, MD; Osamu Akiyama, MD, PhD; Yuzaburo Shimizu, MD, PhD; Takuma Kodama, MD; Ryo Miyahara, MD; Akihide Kondo, MD, PhD; Department of Neurosurgery, Faculty of Medicine, Juntendo University, Tokyo, Japan
Background: Giant arachnoid granulations (GAGs) are large protrusions of arachnoid tissue into the dural venous sinuses, most often the transverse and sigmoid sinuses. They are generally regarded as incidental findings, but in some cases may mimic dural sinus thrombosis or neoplastic lesions on imaging, potentially leading to misdiagnosis and inappropriate treatment. Although increasing recognition of GAGs has been achieved with advanced neuroimaging, their frequency, distribution, and clinical significance remain incompletely understood.
Objective: The purpose of this study was to investigate the dominance pattern of the transverse sinus, the maximal diameter of the transverse and sigmoid sinuses, and the prevalence, size, and distribution of arachnoid granulations, including giant forms, in patients undergoing posterior fossa surgery at our institution.
Methods: We retrospectively analyzed 100 consecutive patients who underwent posterior fossa surgery at Juntendo University Hospital between 2023 and 2024. Preoperative contrast-enhanced MRI and MR venography were reviewed to determine the dominance of the transverse sinus and to measure the maximal diameters of the transverse and sigmoid sinuses. The presence, location, and size of arachnoid granulations were assessed, with GAGs defined as lesions measuring 10 mm or greater in maximal dimension. Clinical records were reviewed for symptoms potentially related to venous outflow obstruction.
Results: Right dominance of the transverse sinus was identified in 46 cases (42.6%), left dominance in 30 cases (27.8%), and no dominance in 32 cases (29.6%). The mean maximal diameter of the transverse sinus was 7.80 mm, while that of the sigmoid sinus was 6.55 mm. Arachnoid granulations were present in 61 cases (56.5%). Among these, six lesions (5.6% of the total cohort, 9.8% of cases with granulations) met criteria for GAGs. Their locations included the right sinus in two patients, the left sinus in two, the midline in one, and bilateral involvement in one. None of the patients demonstrated venous outflow obstruction or clinical symptoms attributable to the presence of GAGs.
Discussion: Our findings demonstrate that arachnoid granulations, including giant forms, are not uncommon in posterior fossa surgery cases. Although asymptomatic in this series, their imaging appearance may closely resemble sinus thrombosis or dural-based tumors, which underlines the importance of accurate recognition. Preoperative awareness of GAGs can prevent unnecessary anticoagulation or surgical interventions and may reduce the risk of intraoperative complications, particularly during approaches involving the transverse or sigmoid sinuses. While no symptomatic cases were encountered in this cohort, prior reports have described associations with headache, tinnitus, or raised intracranial pressure, highlighting the need for further investigation into their potential pathophysiological impact.
Conclusion: GAGs of the transverse and sigmoid sinuses are relatively frequent and occasionally reach giant size. They are clinically significant primarily in the context of differential diagnosis and surgical planning, and should be considered important anatomical variants rather than mere incidental findings.