Unruptured Posterior Cerebral Artery Aneurysm Presenting with Temporal Lobe Epilepsy

The International League Against Epilepsy (ILAE) proposed a new epilepsy classification scheme in 2013. The framework, which was formalized in 2017, builds upon several previous iterations while emphasizing the importance of seizure etiology at each level of classification. However, a recent systematic review reported that “epilepsy of unknown origin” continues to be the most prevalent diagnosis. The same study found structural/ metabolic etiologies account for 40% of cases. Unruptured intracranial aneurysms are often asymptomatic or accompany vague symptoms like headaches; however, they may also cause cranial neuropathies or lead to cerebral ischemia. Giant aneurysms or those that project into cortical surfaces (i.e., the medial temporal lobe) can certainly lead to seizures. Overall, posterior cerebral artery (PCA) aneurysms are uncommon and hence they are very rarely implicated as the cause for seizures. A search of the MEDLINE and EMBASE databases was performed with the specific Medical Subject Headings (MeSH) and keywords for (epilepsy or seizures) and (PCA and intracranial aneurysms). A total of 14 studies were initially identified. Titles and abstracts were screened; studies that described PCA aneurysms presenting with seizures were included. Of the seven remaining studies, two were excluded on further review. One did not have full text available and the other described a mycotic aneurysm located in the calcarine sulcus in the setting of metastatic choriocarcinoma. A summary of the cases is presented in Table 1. Here, we report a patient who experienced stereotypic spells consistent with temporal lobe epilepsy which was caused by an unruptured PCA aneurysm. A 59-year-old left-handed man with a history of dyslipidemia and hypertension presented with episodes consistent with focal aware seizures. The patient described that these events began with a sense of panic and feeling like a curtain was coming down upon him with associated cognitive slowing as if he was wading through water. Soon thereafter, he would develop severe nausea with no emesis. These experiences lasted several minutes without loss of awareness, followed by an immediate return to his cognitive baseline. These events occurred two to three times per week with no identifiable triggers. His neurological examination did not yield focal deficits. The patient was started on carbamazepine 200 mg BID empirically and referred to an epileptologist. A computed tomography angiogram and magnetic resonance imaging revealed a 7 mm aneurysm arising from the P2 segment of the left PCA that was embedded in the medial aspect of the left parahippocampal gyrus with increased signal suggesting inflammation or edema (Figure 1). A cerebral angiogram confirmed the presence of the superolaterally projecting saccular aneurysm (Figure 1). After considering endovascular and open surgical management options, as well as a conservative approach, microsurgical clip repair through a left subtemporal approach was recommended. This decision was based on the aneurysm size, distal location of the aneurysm, significant proximal vascular tortuosity, and small parent artery diameter. Furthermore, the surgical approach would also allow for resection of any local abnormal tissue. The patient underwent neuropsychological evaluation which suggested left hemisphere language dominance and low risk of significant cognitive decline with the proposed lesionectomy without hippocampal resection. An electroencephalogram showed moderate left temporal dysrhythmia seen maximal over the mid to posterior temporal derivations with a variable centroparietal field. These findings indicated focal cerebral dysfunction arising from the area most indicative of an underlying structural abnormality. The surgery proceeded as planned with a left subtemporal craniotomy, clipping of the aneurysm base, and resection of gliotic tissue surrounding the aneurysm dome (Supplementary Figure 1). There was no evidence of adjacent hemosiderin deposition. The postoperative imaging confirmed satisfactory clipping, and the patient remains seizure free 5 months after surgery. He remains on carbamazepine which will be reassessed on his 6-month follow-up.