Joseph Gastala, MD and Bruno Policeni, MD University of Iowa Hospitals and Clinics DISTRIBUTION OF SUBARACHNOID HEMORRHAGE WITH RESPECT TO THE FORAMEN MAGNUM IN RELATION TO RUPTURED INTRACRANIAL ANEURYSMS Poster #: EP-35

DISCLOSURES The authors have no financial or nonfinancial relationships to disclose

OUTLINE Purpose Materials and methods Results Discussion Conclusions

PURPOSE A subarachnoid hemorrhage (SAH) due to ruptured intracranial aneurysm is a devastating clinical event with a high mortality rate and a substantial risk for re-bleeding. It is important that the radiologist not miss a potential aneurysm if the imaging findings suggest a diagnoses To date there have been no studies, to our knowledge, that have compared the distribution of SAH of ruptured intracranial aneurysms with respect to the foramen magnum and we hypothesize that a foramen magnum hemorrhage can be an important clue to the diagnosis of aneurysmal rupture and its location.

MATERIALS AND METHODS A retrospective review of all cases of ruptured aneurysms with SAH at our institution for the last 5 years was performed. Each of the cases was angiographically confirmed Exclusion criteria included: Patients with multiple intracranial aneurysms Patients with prior coiling of a known aneurysm Noncontract CT scan of the brain was performed after large intervals between rupture and CT scanning (after 4 days of the development of symptoms as used by Kallmes et al.) Initial available imaging performed after coil embolization or other intervention Patients for whom no imaging was available for review at our institution The non-contrast CTs of these patients were reviewed to determine the distribution of SAH with attention paid to the foramen magnum.

RESULTS Average age was 60 years old 57 males, 119 females All patients presented with “worst headache of life” but with a minority being found down but previously seen in normal healthy state Anterior communicating artery (Acomm), anterior cerebral artery (ACA), middle cerebral artery (MCA), posterior communicating artery (Pcomm), basilar artery aneurysms and posterior inferior cerebellar artery (PICA) aneurysms were analyzed All superior cerebellar artery (SCA) (1 case) and anterior inferior cerebellar artery (AICA) aneurysm (1 case) cases were excluded as these were in patients with multiple aneurysms Basilar artery aneurysms in this study were all at the basilar tip

FORAMEN MAGNUM HEMORRHAGE AneurysmTotal patientsAfter exclusion criteria Foramen magnum hemorrhage Absence of foramen magnum hemorrhage ACA862 / 6 (25%)4 / 6 (75%) Acomm / 69 (28%)50 / 69 (72%) MCA / 36 (33%)24 / 36 (67%) Pcomm / 29 (37%)18 / 29 (62%) PCA741 / 4 (25%)3 / 4 (75%) Basilar artery / 14 (93%)2 / 14 (14%) PICA / 15 (93%)1 / 15 (7%) Vertebral artery1176 / 7 (86%)1 / 7 (14%) Table 1: Aneurysm rupture with respect to foramen magnum hemorrhage.

AneurysmTotal foramen magnum hemorrhage Complete filling of foramen magnum (>75% cross sectional area) Partial filling of foramen magnum ACA20 / 2 (0%)2 / 2 (100%) Acomm193 / 19 (16%)16 / 19 (84%) MCA122 / 12 (17%)10 / 12 (83%) Pcomm113 / 11 (27%)8 / 11 (73%) PCA10 / 1 (0%)1 / 1 (100%) Basilar artery124 / 12 (25%)8 / 12 (75%) PICA14 10 / 14 (71%)4 / 14 (29%) Vertebral artery66 / 6 (100%)0 / 6 (0%) Table 2: Extent of foramen magnum hemorrhage. Complete filling of the foramen magnum was defined as filling >75% of the cross sectional area on axial slices. Complete filling was more common with posterior fossa aneurysms.

AneurysmTotal casesForamen magnum hemorrhage (% of total cases) Disproportionate supratentorial hemorrhage Foramen magnum hemorrhage without disproportionate supratentorial hemorrhage (% of total cases) ACA62 / 6 (25%)20 / 6 (0%) Acomm6919 / 69 (28%)163 / 69 (4%) MCA3612 / 36 (33%)102 / 36 (6%) Pcomm2911 / 29 (37%)83 / 29 (10%) PCA41 / 4 (25%)10 / 4 (0%) Basilar artery1412 / 14 (93%)84 / 14 (29%) PICA1514 / 15 (93%)0 Vertebral artery76 / 7 (86%)0 Table 3: Adjusting foramen magnum hemorrhages for disproportionate supratentorial hemorrhage. Disproportionate supratentorial hemorrhage was defined as filling of the foramen magnum with subarachnoid blood widening supratentorial subarchnoid spaces. This table shows the number of foramen magnum hemorrhage cases before and after subtracting the disproportionate supratentorial cases.

SUPRATENTORIAL HEMORRHAGE WITHOUT FORAMEN MAGNUM HEMORRHAGE IN ACOMM ANEURYSM RUPTURE A) Axial CT image at the level of the foramen magnum demonstrate no hemorrhage. B) Image at the level of the suprasellar cistern shows hemorrhage within the anterior hemispheric fissure. C) Axial CT image demonstrates large collection of subarachnoid blood from ruptured ACA. ABC

DISPROPORTIONATE SUPRATENTORIAL HEMORRHAGE IN A MCA ANEURYSM RUPTURE A) Axial CT image at the level of the foramen magnum demonstrates partial filling of the foramen magnum. B) Image at the level of the suprasellar cistern hemorrhage within and widening the anterior hemispheric fissure. C) Axial CT image demonstrates widening of the sylvian fissures ABC

DISPROPORTIONATE SUPRATENTORIAL HEMORRHAGE IN A PCOMM RUPTURE A) Axial CT image at the level of the foramen magnum demonstrates partial filling of the foramen magnum. B) Image at the level of the suprasellar cistern hemorrhage within and widening the bilateral MCA fissures. C) Axial CT image demonstrates widening of the sylvian fissures, left greater than right. ABC

PICA ANEURYSM WITH FORAMEN MAGNUM HEMORRHAGE AND MINIMAL SUPRATENTORIAL HEMORRHAGE A) Axial CT image at the level of the foramen magnum demonstrates filling of the foramen magnum. B) Image at the level of the suprasellar cistern demonstrates small hemorrhage within the suprasellar cistern and interpeduncular cistern. C) Axial CT image demonstrates no subrachnoid hemorrhage within sylvian fissures ABC

FORAMEN MAGNUM HEMORRHAGE IN PICA ANEURYSM ABC A) Axial CT image at the level of the foramen magnum demonstrates complete filling of the foramen magnum. B) Image at the level of the suprasellar cistern hemorrhage within the suprasellar cistern, MCA fissures, and. C) Axial CT image demonstrates some subarachnoid hemorrhage within sylvian fissures. Complete filling of the foramen magnum suggests that the ruptured aneurysm is in the lower posterior fossa.

DISCUSSION In our study, we found the presence and extent foramen magnum hemorrhage is a clue to the location of a ruptured aneurysm. Hemorrhage demonstrated within the foramen magnum was more characteristic of posterior fossa aneurysms with 93% of basilar, 93% of PICA and 86% of vertebral artery aneurysms having foramen magnum hemorrhage (Table 1) Of the cases with foramen magnum hemorrhage, complete filling of the foramen magnum was a characteristic predominantly of ruptured aneurysms in the lower posterior fossa, being demonstrated in 71% of our PICA cases and 100% of our vertebral artery cases, but 25% of basilar artery cases. The next most common ruptured aneurysm with foramen magnum hemorrhage to show complete filling was Pcomm 27% (Table 2) However, with PICA aneurysms, still 29% of the cases did not have have complete filling. With several of the other ruptured aneurysms (particularly the MCA and upper posterior circulation) demonstrating cases with partial filling of the foramen magnum hemorrhage another way of distinguishing the lower posterior fossa from the supratentorial aneuryms was explored

DISTINGUISHING HEMORRHAGES When examining hemorrhage within the foramen magnum as well as distribution in the supratentorium, we found that the supratentorial aneurysms as well as the higher posterior fossa aneurysms tended to have widening of some of the subarachnoid spaces We defined disproportionate supratentorial hemorrhage as hemorrhage evident that widened supratentorial subarachnoid spaces along with the incomplete filling of the foramen magnum These spaces included the middle cerebral artery fissures, sylvian fissures, and anterior interhemispheric fissures. Additionally formation of intraparenchymal hematoma was deemed a criteria for disproportionate supratentorial hemorrhage When accounting for a disproportionate amount of hemorrhage within the supratentorium, this helped to distinguish partial filling of the foramen magnum from lower posterior fossa sources as opposed to supratentorial sources

PICA AND VERTEBRAL ARTERY ANEURYSMS AND FORAMEN MAGNUM HEMORRHAGE These data show that PICA and vertebral artery aneurysm ruptures were more likely to have complete filling of the foramen magnum When there is partial filling of the foramen magnum, there is more uncertainty about the location of the hemorrhage. When adjusting the number of cases with foramen magnum hemorrhage with the number of cases that showed disproportionate supratentorial hemorrhage, we were better able to distinguish those cases from ruptured lower posterior fossa aneurysms (Table 3) Particularly, ruptured basilar artery aneurysms frequently resulted in foramen magnum hemorrhage almost as frequently (93%) as PICA and vertebral artery, but also were more likely to result in disproportionate supratentorial hemorrhage. All the studied ruptured aneurysms besides the PICA and vertebral arteries resulted in the majority of the cases resulting in foramen magnum hemorrhage to have disproportionate supratentorial hemorrhage Limitations to the study including the retrospective nature, the relatively low instances of particular ruptured subarachnoid hemorrhage, as well as the non-evaluation of aneurysms such as AICA and SCA. Further study would include more cases as they occur at our institution to have a more robust data set

CONCLUSION Hemorrhage within the foramen magnum may be an indicator of a ruptured PICA or vertebral artery aneurysm rupture, particularly if there is no disproportionate supra- tentorial hemorrhage. Hemorrhage within the foramen magnum and the extent of hemorrhage can be a clue to a lower posterior fossa aneurysm and search should be initiated with such a finding. Additionally, protocols for non-contrast CT and CT angiography should fully include the foramen magnum and the posterior fossa circulation including the PICA to elucidate such findings.

SPECIAL THANKS Special thanks to Dr. Hasan of the Department of Neurosurgery at University of Iowa Hospitals and Clinics for providing the database of ruptured aneurysms at our institution

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