Topological data analysis (TDA) enhances bispectral EEG (BSEEG) algorithm for detection of delirium.

Current methods for screening and detecting delirium are not practical in clinical settings. We previously showed that a simplified EEG with bispectral electroencephalography (BSEEG) algorithm can detect delirium in elderly inpatients. In this study, we performed a post-hoc BSEEG data analysis using larger sample size and performed topological data analysis to improve the BSEEG method. Data from 274 subjects included in the previous study were analyzed as a 1st cohort. Subjects were enrolled at the University of Iowa Hospitals and Clinics (UIHC) between January 30, 2016, and October 30, 2017. A second cohort with 265 subjects was recruited between January 16, 2019, and August 19, 2019. The BSEEG score was calculated as a power ratio between low frequency to high frequency using our newly developed algorithm. Additionally, Topological data analysis (TDA) score was calculated by applying TDA to our EEG data. The BSEEG score and TDA score were compared between those patients with delirium and without delirium. Among the 274 subjects from the first cohort, 102 were categorized as delirious. Among the 206 subjects from the second cohort, 42 were categorized as delirious. The areas under the curve (AUCs) based on BSEEG score were 0.72 (1st cohort, Fp1-A1), 0.76 (1st cohort, Fp2-A2), and 0.67 (2nd cohort). AUCs from TDA were much higher at 0.82 (1st cohort, Fp1-A1), 0.84 (1st cohort, Fp2-A2), and 0.78 (2nd cohort). When sensitivity was set to be 0.80, the TDA drastically improved specificity to 0.66 (1st cohort, Fp1-A1), 0.72 (1st cohort, Fp2-A2), and 0.62 (2nd cohort), compared to 0.48 (1st cohort, Fp1-A1), 0.54 (1st cohort, Fp2-A2), and 0.46 (2nd cohort) with BSEEG. BSEEG has the potential to detect delirium, and TDA is helpful to improve the performance.

Mechanical Thrombectomy for Basilar Artery Occlusion Compared with Anterior Circulation Stroke.

OBJECTIVE: To investigate the clinical effectiveness of mechanical thrombectomy (MT) for basilar artery occlusion (BAO) and to ascertain whether outcomes for patients with BAO were comparable to those with anterior circulation large vessel occlusion (ACS). METHODS: A total of 345 patients who underwent MT between 2011 and 2018 were grouped by occlusion site (295 patients with ACS and 50 patients with BAO). Patients' baseline characteristics, procedural times, complications, symptomatic intracranial hemorrhage, modified Rankin Scale score, and mortality at 90 days were analyzed. RESULTS: Male preponderance (66.0% vs. 48.8%; P = 0.0316), younger age (72.5 years [interquartile range (IQR), 64.75-78.5 years] vs. 77 years [IQR 69-84 years]; P = 0.0297), higher National Institutes of Health Stroke Scale score (24.5 [IQR, 13-32] vs. 18 [IQR 13-22]; P = 0.0015) and higher reperfusion rate (100% vs. 84.7%; P = 0.0010) were observed in patients with BAO. We found no significant difference in favorable outcomes (modified Rankin Scale score ≤2) between patients with BAO and patients with ACS (64.3% vs. 49.3%; P = 0.0914). In multivariate analysis, Alberta Stroke Program Early Computed Tomography Score (odds ratio [OR], 1.282; 95% confidence interval [CI], 1.090-1.524; P = 0.0024), time from onset to reperfusion (OTR) (OR, 0.9950; 95% CI, 0.992-0.998; P = 0.0008), successful reperfusion (OR, 6.953; 95% CI, 1.576-48.729; P = 0.0092), and hemorrhagic complication (OR, 0.352; 95% CI, 0.151-0.797; P = 0.0122) were associated with a favorable outcome at 90 days in patients with ACS. In patients with BAO, only OTR (OR, 0.9879; 95% CI, 0.974-0.999; P = 0.0314) was associated with a favorable outcome at 90 days. CONCLUSIONS: MT may be considered the standard care for patients with BAO. OTR was the only common significant predictor for favorable outcomes in both patient cohorts.

Mechanical Thrombectomy of Primary Distal Anterior Cerebral Artery Occlusion: A Case Report.

OBJECTIVE: Primary anterior cerebral artery (ACA) occlusion is a rare condition and sometimes leads to significant neurological deficits. We herein report on the efficacy of mechanical thrombectomy (MT) in treating the distal ACA occlusion in a clinical setting. CASE PRESENTATION: A 76-year-old woman presented with a sudden onset of right hemiparesis. Computed tomographic angiography and perfusion imaging and subsequent analysis with RAPID software revealed acute left ACA occlusion with salvageable penumbra. The patient obtained a score of 11 on the National Institutes of Health Stroke Scale. MT was performed for occlusion of the left ACA (A4), and successful reperfusion (Thrombolysis in Cerebral Infarction score of 3) was achieved on the first attempt using a stent retriever. The patient's recovery progressed well, and she was discharged 13 days after admission with a modified Rankin Scale score of 1. CONCLUSION: This case report demonstrates the clinical efficacy, safety, and favorable clinical outcome of treating a primary distal ACA occlusion with MT.

A Direct Aspiration First Pass Technique in Japanese Real-World Clinical Setting.

BACKGROUND: It is debatable whether mechanical thrombectomy has benefits in a real-world setting outside the more rigid and selective clinical trial environment. OBJECTIVE: To evaluate clinical outcomes, efficacy, and safety of mechanical thrombectomy in single-center retrospective cohort case series. METHODS: We reviewed prospectively collected data from our large-vessel occlusion stroke database to identify patients undergoing mechanical thrombectomy using Penumbra catheters (Penumbra, Almeida, California) as first-line devices. The primary outcomes were the modified Rankin Scale score at 90 d and recanalization rate. The secondary outcomes included the rates of hemorrhagic complications and mortality. RESULTS: The entire study population included 298 patients. Thrombolysis in Cerebral Infarction Scale ≥2b was achieved in 86.6% of patients. Fifty-five patients (18.5%) were outside the 6 hr time window and 82 patients (27.5%) were over 80-yr old. The posterior circulation thrombectomy rate was 12.4%. At 90 d from onset, 49.3% of patients had favorable outcomes. The parenchymal hemorrhage type 2 (PH2) and subarachnoid hemorrhage rates were 2.3% and 11.7%, respectively. In multivariate analyses, cerebral blood flow/cerebral blood volume mismatch (odds ratio [OR] = 9.418; 95% confidence interval [CI], 3.680-27.726; P < .0001), onset to recanalization time (OR = 0.995; 95% CI, 0.991-0.998; P = .0003), and hemorrhagic complications including PH2 and subarachnoid hemorrhage (OR = 0.186; 95% CI, 0.070-0.455; P = .0002) were associated with favorable outcomes. CONCLUSION: A direct aspiration first pass technique with an adjunctive device demonstrated high recanalization rates in old Japanese patients. Our patient cohort may reflect the application of endovascular techniques in acute ischemic stroke treatment in a real-world setting.

Mechanical Thrombectomy for Acute Anterior Cerebral Artery Occlusion.

BACKGROUND: We sought to examine the presentation, treatment, and outcomes of anterior cerebral artery (ACA) occlusions in patients undergoing mechanical thrombectomy (MT). METHODS: Two-hundred ninety-eight consecutive patients with large-vessel occlusion treated with MT were analyzed to identify all patients with acute ACA occlusion who underwent MT. The primary end point was defined as achieving a thrombolysis in cerebral infarction score ≥2b. The secondary end point included the 90-day modified Rankin Scale (mRS) score and symptomatic intracranial hemorrhage. RESULTS: Nine patients with a median National Institutes of Health Stroke Scale score of 24 presented with acute ACA occlusion. The median time from onset to recanalization was 229 minutes. The ACA occlusion was a primary embolic occlusion in 5 patients, secondary to an interventional maneuver in 4 patients. Recanalization (thrombolysis in cerebral infarction ≥2b) was achieved in 9 of 9 patients (100%) without procedural complications. All patients had a 90-day mRS score ≥3, and 2 patients had an mRS score of 6. Two patients developed hemorrhagic infarction, and 1 patient had subarachnoid hemorrhage. CONCLUSIONS: Although MT can be considered in patients with ACA occlusions, our data suggest that future clinical trials are needed to determine the efficacy of MT for ACA occlusions. Unfavorable outcomes in our study were considered to occur because of a larger infarct volume due to internal carotid artery, middle cerebral artery, and anterior cerebral artery territory infarction. The time from onset to recanalization was longer because MT was performed for occlusions of multiple arteries.

Recurrence in 787 Patients with Chronic Subdural Hematoma: Retrospective Cohort Investigation of Associated Factors Including Direct Oral Anticoagulant Use.

OBJECTIVE: Chronic subdural hematoma (CSDH) is a highly recurrent disorder. Although some predictors including the use of antithrombotic agents such as aspirin and warfarin have been proposed, the pathogenic mechanism involved remains unclear. Moreover, the link between direct oral anticoagulant (DOAC) agent use and CSDH recurrence has not been reported. The aim of this study was to investigate factors including DOAC use that could potentially be associated with CSDH recurrence. METHODS: The authors analyzed 787 patients with CSDH who underwent surgery for CSDH with 1 burr-hole irrigation at Baba Memorial Hospital from January 2012 to November 2017. The patients were divided into recurrence and nonrecurrence groups and anticoagulant, antiplatelet, and control groups. Recurrence was defined as ipsilateral hemorrhage within 90 days from the original operation. Variables with P < 0.1 in the univariate analysis were included in a multivariate logistic regression model. RESULTS: CSDH recurrence was observed in 12.2% of patients, and significantly more men (80.2%) than women experienced recurrence. Age, sex, and warfarin use were entered in the multivariate analysis, and it was revealed that age and male sex were independently associated with CSDH recurrence. Antithrombotic agent use including use of DOACs was not associated with increased CSDH recurrence. CONCLUSIONS: The present study found that age and male sex were independently associated with CSDH recurrence, while the use of antithrombotic agents was not.

Basilar Artery Occlusion with "Seizures" as a Presenting Symptom: Three Cases Treated Using Mechanical Thrombectomy.

BACKGROUND: Basilar artery occlusion (BAO) is a rare, potentially fatal cause of ischemic stroke. It is often challenging to diagnose, especially when the presenting symptom is "seizures". We present 3 cases of patients with BAO presenting with seizures. CASE DESCRIPTION: The first patient was a 53-year-old man with clonic convulsions. On angiography, BAO was detected and mechanical thrombectomy (MT) was performed. The modified Rankin Scale score at 3 months after treatment was 1. The second patient was a 64-year-old man with generalized convulsions. He was diagnosed with BAO and vertebral artery dissection and was treated with MT, percutaneous transluminal angioplasty, and stenting. The modified Rankin Scale score at 3 months after treatment was 3. The third patient was a 77-year-old man with tonic convulsions. He was diagnosed with BAO and treated with MT. However, he did not survive. CONCLUSIONS: BAO is devastating; however, it is a treatable disease. Our report suggests that BAO should be suspected in patients presenting with initial convulsive seizures.

A case of delayed distal coil migration after coil embolization of an unruptured distal azygos anterior cerebral artery aneurysm: A case report and literature review.

Intraprocedural coil migration during endovascular treatment for an aneurysm that might carry serious ischemic complications is well known. On the other hand, delayed coil migration after endovascular treatment for an aneurysm is very rare. A 77-year-old woman was incidentally diagnosed with unruptured aneurysm associated with distal azygos anterior cerebral artery (ACA). The aneurysm was located at the distal bifurcation of the azygos ACA and was wide necked (approximately 7 mm in diameter). Endovascular coil embolization was selected and the aneurysm was occluded successfully, but 29 days after endovascular therapy, follow-up computed tomography (CT) and magnetic resonance (MR) angiography revealed distal coil migration in the peripheral portion of the ACA. In addition, CT on day 57 after therapy revealed the migrated coil had moved more distally. Fortunately, in the course of these events, the patient remained asymptomatic. To the best of our knowledge, this represents the first case of delayed distal coil migration associated with relatively rare azygos ACA aneurysm, and also the first report confirming more distal coil movement over time. In the future, a large number of patients could develop this complication as more aneurysms are aggressively treated with endovascular treatment. Knowledge regarding the possibility of delayed coil migration is thus important.

[Coil Embolization for Very Small Intracranial Aneurysms with Diameter Less than 3mm:A Case Series of 14 Patients and Literature Review].

INTRODUCTION: Many studies describe aneurysms measuring ≤3mm as "very small" or "tiny, " with a risk of intraoperative rupture higher than that of most cerebral aneurysms. We evaluated the results of endovascular coil embolization for very small aneurysms with diameter ≤3mm. MATERIAL AND METHODS: The same interventional neurosurgeon performed coil embolization for 14 tiny aneurysms in 14 patients(8male and 6 females)at our institution between May 2015 and June 2017. Patient age range was 42-88 years(average 65.6 years). Five aneurysms had ruptured and 9 were unruptured. Of the 9 unruptured aneurysms, 3 were associated with a previous ruptured aneurysm. We assessed the procedural complications, type of microcatheter and coils used, total number and length of coils, and angiographic results immediately after the procedure. RESULTS: In 14 aneurysm cases, 8 used only 1 pre-shaped microcatheter, 4 used 2, and 2 used 3;cases using multiple microcatheters added final shaping. Only one case used a helical first coil and the remaining 13 cases used a 3-dimensional coil. The number of coils used was 1 in 3 cases, 2 in 7 cases, 3 in 2 cases, and 4 in 2 cases. The total length of coils inserted was <5 cm in 5 cases, 5-10 cm in 5 cases, and >10 cm in 4 cases. The total length of coils used was <10cm in 70% of cases. Immediately after coil embolization, complete occlusion and a neck remnant were achieved in 11 and 3 cases, respectively. Ballooning was induced by intentionally introducing a balloon-assist technique during surgery in 7 cases, and the balloon was actually inflated in 4 cases. Complications were seen in 2 ruptured cases;1 had an intraoperative rupture, the other had parent artery occlusion, and both patients recovered. CONCLUSION: Coil embolization for tiny aneurysms can be performed comparatively safely by understanding the pitfalls and by using appropriate procedures and tools. Placing the catheter tip at the aneurysm neck is the first step and endovascular treatment is usually performed with ≤3 coils measuring ≤10 cm in total length. Complete embolization should be attempted, but even incomplete embolization is acceptable. More delicate coil embolization is required.

Optimal thresholds for ischemic penumbra predicted by computed tomography perfusion in patients with acute ischemic stroke treated with mechanical thrombectomy.

BACKGROUND AND PURPOSE: Optimal thresholds for ischemic penumbra detected by CT perfusion (CTP) in patients with acute ischemic stroke (AIS) have not been elucidated. In this study we investigated optimal thresholds for salvageable ischemic penumbra and the risk of hemorrhagic transformation (HT). METHODS: A total of 156 consecutive patients with AIS treated with mechanical thrombectomy (MT) at our hospital were enrolled. Absolute (a) and relative (r) CTP parameters including cerebral blood flow (aCBF and rCBF), cerebral blood volume (aCBV and rCBV), and mean transit time (aMTT and rMTT) were evaluated for their value in detecting ischemic penumbra in each of seven arbitrary regions of interest defined by the major supplying blood vessel. Optimal thresholds were calculated by performing receiver operating characteristic curve analysis in 47 patients who achieved Thrombolysis In Cerebral Infarction (TICI) grade 3 recanalization. The risk of HT after MT was evaluated in 101 patients who achieved TICI grade 2b-3 recanalization. RESULTS: Absolute CTP parameters for distinguishing ischemic penumbra from ischemic core were as follows: aCBF, 27.8 mL/100 g/min (area under the curve 0.82); aCBV, 2.1 mL/100 g (0.75); and aMTT, 7.30 s (0.70). Relative CTP parameters were as follows: rCBF, 0.62 (0.81); rCBV, 0.83 (0.87); and rMTT, 1.61 (0.73). CBF was significantly lower in areas of HT than in areas of infarction (aCBF, p<0.01; rCBF, p<0.001). CONCLUSIONS: CTP may be able to predict treatable ischemic penumbra and the risk of HT after MT in patients with AIS.

[Five Cases of Neuroendovascular Treatment Using the Goose Neck Snare for Inducing and Holding the Guiding Catheter].

The stabilization of a guiding catheter is a very important factor for successful endovascular treatment. However, it is sometimes difficult to obtain sufficient stabilization because of the tortuosity of the approach route. A Goose Neck Snare is useful for the retrieval of intravascular foreign bodies and can be used to hold the guiding catheter. We describe five cases of endovascular treatment performed while using the Goose Neck Snare via the brachial artery to hold the guiding catheter. We discuss the utility of this strategy.

A case with coil embolization for ruptured aneurysm associated with fenestration of the posterior inferior cerebellar artery.

An 87-year-old man hospitalized for subarachnoid hemorrhage showed a ruptured aneurysm arising from fenestration of the posterior inferior cerebellar artery. Endovascular treatment was selected and the aneurysm and superior limb were embolized completely using three coils. Fenestration of the posterior cerebellar artery is exceedingly rare. In addition, we present a first case of aneurysm as fenestration of the posterior inferior cerebellar artery that was definitively identified as a cause of bleeding.

Mechanical Thrombectomy for Acute Basilar Artery Occlusion in Early Therapeutic Time Window.

BACKGROUND: The natural history of basilar artery occlusion (BAO) is devastating, with morbidity rates increasing up to 80%. However, the efficacy of recanalization therapy for BAO has not been established as yet. OBJECTIVE: We analyzed consecutive cases of BAO treated with mechanical thrombectomy (MT) to evaluate its safety and efficacy and to determine factors associated with the prognosis. METHODS: Between October 2011 and September 2016, MT was performed in 34 patients with BAO. MT was performed using the Penumbra system and stent retriever. CT perfusion was used for evaluating patients. Cerebral blood flow (CBF) maps and cerebral blood volume (CBV) maps were evaluated. CBF/CBV mismatch was defined as ≥50% penumbra. Clinical outcomes were correlated with demographic, clinical, and radiographic findings. RESULTS: The median baseline National Institutes of Health Stroke Scale score was 29 (14-33). The recanalization rate (≥thrombolysis in cerebral infarction grades 2b) was 100%. The median onset to recanalization time (OTR) was 197 (160-256) min. Favorable outcomes (modified Rankin Scale ≤2) at 90 days occurred in 56% (n = 19 of 34). The mortality rate at 90 days was 12% (n = 4 of 34). In univariate analysis, intravenous (IV) recombinant tissue-type plasminogen activator (rt-PA) use, and OTR were significantly associated with favorable outcomes. In a multivariate logistic regression model, IV rt-PA use and lower National Institute of Health Stroke Scale score were significantly related to favorable outcomes. Conclusion and Relevance: Multimodal endovascular therapy using the Penumbra system and stent retriever demonstrated a high recanalization rate and favorable outcomes for BAO. Both devices were feasible and effective in the treatment of BAO. An approach combining MT with IV thrombolysis provided a better recanalization rate and more favorable clinical outcomes.

[Usefulness of Edoxaban for Deep Cerebral Venous Sinus Thrombosis with Hemorrhagic Infarction:A Case Report].

We describe a case of deep cerebral venous sinus thrombosis(DCVST)that was successfully treated by oral administration of the Xa inhibitor edoxaban. A 53-year-old man was admitted to our hospital because of a headache and undifferentiated dizziness. Computed tomography(CT)demonstrated a low-density area in the bilateral thalamus and high-density lesions in the internal cerebral veins(ICVs)and vein of Galen. Magnetic resonance imaging with diffusion-weighted images detected areas of hyperintensity in the bilateral thalamus. Additionally, the inferior sagittal sinus, ICV, and vein of Galen were not detected by CT venography or cerebral angiography. We therefore diagnosed DCVST and started anticoagulation therapy with heparin(IV)and warfarin. A week after admission, lesions that showed hypointensity on T2* images and high density on CT scans were detected in the bilateral thalamus. We thought that hemorrhagic infarction had occurred in association with DCVST, and changed the anticoagulation therapy to oral administration of edoxaban on day 9. The patient's symptoms gradually diminished, and CT venography indicated partial recanalization of the DCV from the ICV to the vein of Galen on day 72. We report our experience, and discuss the safety and usefulness of the Xa inhibitor for treating DCVST with hemorrhagic infarction.

[A Case of Middle Cerebral Artery Stenosis Presented with Limb-Shaking TIA].

Involuntary movement is a rare clinical manifestation of transient ischemic attack (TIA). However, limb-shaking TIA is well described presentation of carotid occlusive disease. We present the case of a patient who developed limb-shaking TIA associated with high-grade stenosis of middle cerebral artery (M1), which was treated with percutaneous transluminal angioplasty (PTA). The procedure was performed successfully without complication and the symptom disappeared immediately after the procedure. The patient remained free of symptoms at the 38-month follow-up. There was no tendency of restenosis of M1. In this case, PTA was technically feasible and beneficial for limb-shaking TIA with M1 stenosis. Limb-shaking TIA can be a symptom of high-grade stenosis of M1.

[A Girl with Intraorbital Varix: A Case Report].

We report a case of intraorbital varix. A 16-year-old girl showed sudden left-sided exophthalmos after vomiting. After several episodes of vomiting, she developed complete loss of vision in the left eye, followed by orbital pain, disruption of eye movement, and periorbital swelling. No change in symptoms or signs was observed after the Valsalva maneuver or jugular vein compression. Computed tomography (CT), magnetic resonance imaging (MRI), and angiography were inconclusive. Transcranial surgery revealed a large varix near the optic nerve. The lesion could not be completely resected because the orbital fat interfered with its complete visualization. We cauterized the lesion to reduce its volume. The patient's symptoms improved markedly after surgery and cauterization. Thus, cauterization appears to be an effective strategy to reduce the volume of an unresectable intraorbital varix.

[Contralateral suboccipital approach for clipping of an unruptured vertebral artery-posterior inferior cerebellar artery aneurysm].

Numerous approaches have been used to access aneurysms of the vertebral artery(VA)-posterior inferior cerebellar artery(PICA)complex for microsurgical clipping. Here, we report the case of a patient with an unruptured aneurysm of the left VA-PICA complex that was successfully treated using a contralateral suboccipital approach. Computed tomography angiography demonstrated a small saccular aneurysm arising from the lateral aspect of the left V4 segment just distal to the PICA origin. The aneurysm deviated to the right from the midline at the level of the jugular tubercle on angiographic evaluation, so we selected a contralateral suboccipital approach. The aneurysm was completely obliterated by neck clipping. After surgery, slight dysphagia and hoarseness appeared, but dysphagia disappeared within several days and hoarseness disappeared within 5 months. VA-PICA aneurysms can vary in their relationship to cranial nerves, brainstem, and bones of the skull base. Neurosurgeons should consider using a contralateral approach for certain aneurysms arising from a tortuous VA that has crossed the midline.

Risk of rebleeding in arteriovenous malformations due to impaired venous drainage after radiosurgery.

A 27-year-old woman presented with rebleeding from an intracranial arteriovenous malformation (AVM) 6 years after radiosurgery. Cerebral angiography demonstrated venous drainage change into a single drainer and cortical reflux due to drainage occlusion into the superior sagittal sinus. During surgery, multiple small feeders thought to be occluded on preoperative angiography caused brain swelling, hindering resection of the AVM border plane. Flow changes after radiosurgery, especially impaired venous drainage, may have increased the tendency to rebleeding of the AVM. Scheduled angiography after radiosurgery is recommended, and retreatment for residual AVMs is preferable, especially if venous drainage change occurs.

[A case of petrous ridge meningioma manifested as pneumocephalus followed by Eustachian tube insufflation].

A 50-year-old female, who had a headache after Eustachian tube insufflation for her ear congestion, came to our hospital. CT and MRI revealed pneumocephalus and petrous ridge meningioma which destroyed petrous bone and air cells. Eustachian tube insufflation was considered to make the air coming into the middle ear, mastoid air cell and then into the intracranial space destroying the tumor. At surgery, there was subdural hematoma around the tumor. Total removal of the tumor and the hematoma membrane was performed. Histologically, the tumor was transitional meningioma and the cluster of meningioma cells were noted in the subdural hematoma membrane.

[Four cases of direct surgery for anterior inferior cerebellar artery aneurysms].

Anterior inferior cerebellar artery (AICA) aneurysms are very rare. We carried out four direct operations for AICA aneurysms including two distal AICA aneurysms using lateral suboccipital retrosigmoid approaches (LSRA). We successfully performed the clipping by LSRA. but hearing loss occurred except in one of our cases which involved a chronic term operation in in our cases, In a 72 years old female with a ruptured dissecting aneurysm of the AICA anterior pontine segment, we performed the OA-PICA anastomosis first because of its being an AICA-PICA type, and then we continued to carry out the trapping operation of dissecting artery on day 0. She left our hospital cheerfully but hearing loss persisted on the operated side. Four examples of the dissecting aneurysm of AICA anterior pontine segment have been reported, but only our case involved the trapping with revascularization in acute stage. At the moment, there is no clinical or useful classification for distal AICA aneurysm because it is extremely rare. We will now propose a new classification. This classification is divided into two groups, (1) P (pons) -group and (2) C (cerebellum) -group. The P-group consists of pA (AICA anterior pontine segment). pL (lateral branch on the pons to the meatal loop) and pM (medial branch on the pons). C-group consists of m-loop (meatal loop), cL (lateral branch post meatal loop) and cM (medial branch on the cerebellum). From results of case reports (75 distal AICA aneurysms), we found that pA: 5 (6.7%), pL: 2 (2.8%), pM: 0, m-loop: 54 (72%), cL: 8 (11%), cM: 6 (8.3%). The followings factors were also found. (1) Occlusion of the parent artery of P-group without revascularization of peripheral circulation may entail the risk of death. (2) On the other hand, as for the C-group, the parent artery was able to be occluded without severe consequences, but hearing loss and/or cerebellar infarction occurred. We believe that this classification is simple and very useful for therapeutic strategies in both direct surgery and intravascular treatments for distal AICA aneurysms.