Ruptured aneurysm in collateral arteries with blood-flow impairment of posterior inferior cerebellar artery: a report of three cases.

Herein, we report three cases of cerebellar hemorrhage due to a ruptured small aneurysm located on a collateral artery compensating for one or more stenotic or occluded major cerebellar arteries. In each case, endovascular distant parent artery occlusion of both the collateral artery and aneurysm was performed to prevent rebleeding. A ruptured small aneurysm in a collateral artery may be observed in patients with hemorrhage in an atypical cerebellar region, especially in cases of stenosis or occlusion of the vertebral artery or posterior inferior cerebellar artery. Thus, cerebral angiography is recommended to rule out collateral artery aneurysm.

Posterior Inferior Cerebellar Artery Aneurysm Shaped Like a "Calabash Gourd" and Mimicking a Tumor.

Posterior inferior cerebellar artery aneurysms are likely to be fusiform, yet they hardly enlarge to mimic a tumor in the posterior fossa on radiology. They constitute about 3%-4% of all cerebral aneurysms. A 65-year-old woman presented with tremor in her right upper limb for 1 year and intermittent dizziness for 8 months. Interestingly, magnetic resonance imaging revealed 2 unanimously enhanced masses like mother and daughter located in the right cerebellum hemisphere. The lesion was resected via surgery, and histopathology established the diagnosis of an aneurysm. Her tremor and dizziness subsided 3 months after the surgery, and at her 2-year follow-up she was well with no further neurologic deficits.

Flow Diversion for Treatment of Anterior Inferior Cerebellar Artery Aneurysms: Mechanism and Pitfalls from a Novel Management Strategy.

BACKGROUND: Anterior inferior cerebellar artery (AICA) aneurysms present a challenge for neurosurgeons and neurointerventionalists alike. METHODS: Cases of AICA aneurysms managed with endovascular flow diversion at our institute are reviewed with their angiographic outcomes. RESULTS: Both direct and indirect flow diversion provide complete aneurysm occlusion at follow-up. We propose a stratified method of approaching AICA aneurysms based on location, rupture status, and neck size. CONCLUSIONS: Careful evaluation of preoperative parameters is paramount in deciding between a surgical or a neuroendovascular approach. Low-profile stents in the future may assist in direct flow diversion of AICA trunk aneurysms. In addition, neurosurgeons need to be well versed in endovascular approaches.

Preserving the cerebellar hemispheric tentorial bridging veins through a novel tentorial cut technique for supracerebellar approaches.

OBJECTIVE: The objective of this study was to describe the distribution pattern of cerebellar hemispheric tentorial bridging (CHTB) veins on the tentorial surface in a case series of perimedian or paramedian supracerebellar approaches and to describe a novel technique to preserve these veins. METHODS: A series of 141 patients with various pathological processes in different locations was operated on via perimedian or paramedian supracerebellar approaches by the senior author from July 2006 through October 2022 and was retrospectively evaluated. During surgery, the number and locations of all CHTB veins were recorded to establish a distribution map on the tentorial surface, divided into nine zones. Patients were classified into four groups according to the surgical technique used to manage CHTB veins: 1) group 1 consisted of CHTB veins preserved without intervention during surgery or no CHTB veins found in the surgical route; 2) group 2 included CHTB veins coagulated during surgery; 3) group 3 included CHTB veins preserved with arachnoid and/or tentorial dissection from the cerebellar or tentorial surface, respectively; and 4) group 4 comprised CHTB veins preserved using a novel tentorial cut technique. RESULTS: Overall, 141 patients were included in the study. Of these 141 patients, 38 were in group 1 (27%), 32 in group 2 (22.7%), 47 in group 3 (33.3%), and 24 in group 4 (17%). The total number of CHTB veins encountered was 207 during surgeries on one side. According to the distribution zones of the tentorium, zone 5 had the highest density of CHTB veins, while zone 7 had the lowest. Of the patients in group 4, 6 underwent the perimedian supracerebellar approach and 18 had the paramedian supracerebellar approach. There were 39 CHTB veins on the surface of the 24 cerebellar hemispheres in group 4. The tentorial cut technique was performed for 27 of 39 CHTB veins. Twelve veins were not addressed because they did not present any obstacles during approaches. During surgery, no complications were observed due to the tentorial cut technique. CONCLUSIONS: Because there is no way to determine whether a CHTB vein can be sacrificed without complications, it is important to protect these veins in supracerebellar approaches. This new tentorial cut technique in perimedian or paramedian supracerebellar approaches makes it possible to preserve CHTB veins encountered during supracerebellar surgeries.

Bypass Surgery for Vertebral Artery and Posterior Inferior Cerebellar Artery Fusiform Aneurysms: Surgical Technique and Key Lessons.

Fusiform vertebral artery (VA) aneurysms are challenging to treat due to their pathophysiology, morphology, and anatomic location.1,2 Endovascular treatments are considered to be a widely adopted safe option for this pathology.1 Open microsurgical treatment is considered for complex anatomy, important branch involvement, poor collateral flow, or failed endovascular therapy.3-7 This report aims to show the flow-replacement strategy and bypass technique for a VA aneurysm with complex anatomy and branch involvement. A 24-year-old man presented to our clinic with a bilateral fusiform VA aneurysm discovered during workup of progressive headaches. Further investigation revealed that the left-side aneurysm was mostly thrombosed and the posterior inferior cerebellar artery arose from the aneurysm dome with a fusiform enlargement within a few millimeters from the branching point. After evaluating all management options, the patient decided on surgical treatment of the left VA aneurysm. We performed an occipital artery to posterior inferior cerebellar artery end-to-side anastomosis distal to the fusiform enlargement, followed by trapping of the aneurysm and dome resection (Video 1). Antegrade flow to the distal VA was reestablished using a radial artery interposition graft, thus preventing any flow alterations that may cause growth or rupture of the contralateral aneurysm caused by increased hemodynamic stress if the ipsilateral VA flow is not preserved.8 After in-hospital physical rehabilitation, the patient was discharged with a modified Rankin Scale score of 1. The contralateral aneurysm is managed with serial imaging and treatment will ensue if there is clinical-radiologic evolution. The patient consented to the procedure and publication of his image.

Endoscopic endonasal transclival clipping of a cerebellar arteriovenous malformation feeding vessel and associated aneurysm; a 2D operative video.

Positioned along the ventral surface of the pons, proximal superior cerebellar artery (SCA) aneurysms account for only 1.7% of all intracranial aneurysms [1]. Unlike more commonly encountered basilar artery aneurysms, patients often experience good outcomes when treated via endovascular coiling or surgical clipping [1,2]. These lesions frequently have a lateral projection and paucity of perforator arteries [2]. With further development of endoscopic endonasal techniques, access to this region is possible via a direct frontal exposure to the ventral brainstem, basilar artery and branching vessels. To date, there are only a limited number of reports describing an endoscopic endonasal transclival (EETC) approach for surgical clipping [3-5]. In this operative video, we detail the surgical clipping of a cerebellar arteriovenous malformation feeding vessel and an associated aneurysm using the EETC approach in a 59-year-old woman who presented with sudden onset of a severe headache. The feeding vessel and aneurysm's midline location, just below the take-off of the SCA made it a good candidate for this surgery. Major steps included in this video include 1) transsphenoidal exposure of and subsequent drilling of the clivus, 2) dural opening into the pre-pontine cistern and dissection of the aneurysm, 3) clipping of the aneurysm, and 4) multi-layered closure of the skull base defect. Overall, the patient tolerated the procedure well and was found to have no residual filling of the aneurysm or the AVM feeding vessel at 2-year follow-up. EETC is a viable surgical option for the treatment of aneurysm located along the midline of the pre-pontine cistern.

Ring-shaped Dandy's superior petrosal vein.

BACKGROUND: Dandy's superior petrosal vein (SPV) anatomy is highly relevant for neurosurgeons. The SPV drains into the superior petrosal sinus (SPS), closely related to the trigeminal and internal auditory pores. METHOD: The archived enhanced MRI files of a male patient were studied. RESULTS: An infratentorial ring-shaped (RS) SPV was found on the petrosal surface of the right cerebellar hemisphere. It was inserted in the SPS above the internal auditory pore, postero-lateral to the trigeminal pore. The anterior arm of that venous ring received a delicate supratrigeminal plexus of veins from the pontine surface and continued as a single venous trunk on the cerebellar surface. CONCLUSION: Such previously unreported RS-SPV is of utmost importance to be identified before subtemporal transtentorial and retrosigmoid approaches for different neurosurgical reasons.

Use of Proximal Suboccipital Segment of Occipital Artery as Donor for Posterior Circulation Revascularization Surgery: Technical Note.

BACKGROUND: The distal suboccipital segment of the occipital artery is commonly used as a donor vessel for aneurysms of the posterior circulation requiring revascularization techniques. Isolating this segment of vessel can be challenging due to its course in and out of the various layers of the suboccipital musculature. METHODS: We describe the use of the proximal suboccipital segment of the occipital artery within the occipital groove at the lateral skull base as a donor segment for an interposition graft in revascularization surgery. We present a case detailing the use of this technique for treatment of a dissecting PICA aneurysm and photographs from cadaveric dissections demonstrating relevant anatomy. RESULTS: Our patient is a 62-year-old man who presented with a high-grade subarachnoid hemorrhage from a proximal dissecting-type aneurysm of the posterior inferior cerebellar artery (PICA). Endovascular options were limited to coil sacrifice of the parent vessel, and thus the patient was taken for a far lateral craniotomy, trapping of the aneurysm, and revascularization of the PICA territory via a saphenous vein interposition graft sewn proximally and distally to the occipital artery within the occipital groove and a cortical segment of the affected PICA, respectively. Postoperative imaging demonstrated filling of the PICA territory via the graft, and the patient ultimately recovered from his subarachnoid hemorrhage. CONCLUSIONS: The use of the proximal suboccipital segment of the occipital artery is a viable option for a donor in posterior fossa revascularization surgery.

Bilateral duplicated hypoplastic superior cerebellar arteries one of which originates from a full-type fetal posterior cerebral artery.

PURPOSE: The association of bilateral duplication of the superior cerebellar artery with an origin from the posterior cerebral artery is rare but of great interest to anatomists, radiologists, and surgeons. This article reports bilateral duplicated hypoplastic superior cerebellar arteries, one of which arises from a full-type fetal cerebral artery. MATERIAL AND METHOD: A 59-year-old woman admitted to the neurosurgery department for a subarachnoid hemorrhage underwent a brain CTA with 3D reconstruction using «3D slicer 4.11¼ software. Brain CTA and the 3D model were used to analyze the configuration of the posterior circulation. RESULTS: CTA images and the 3D model showed an unusual configuration of the posterior circulation. The basilar artery prolonged the left vertebral artery, while the right vertebral artery ended in the right posterior inferior cerebellar artery. On both sides, a full-type fetal posterior cerebral artery and duplicated hypoplastic superior cerebellar artery were observed. Three cerebellar arteries arose from the basilar artery, while the fourth one emerged from the right fetal posterior cerebral artery. CONCLUSION: Knowledge of such a configuration of the posterior circulation and others is necessary before radiological and surgical procedures. It helps to understand hemodynamic events, and neurovascular conflicts, improve revascularization procedures, and avoid surgical arterial and nervous injuries.

Occipital artery-posterior inferior cerebellar artery bypass: a cadaveric feasibility study.

PURPOSE: To demonstrate that occipital artery (OA)-p1 posterior inferior cerebellar artery (PICA) bypass can be an alternative for complex posterior circulation aneurysms. METHODS: A far-lateral approach to craniotomy was performed on 20 cadaveric specimens, and the OA was obtained 'in-line.' Its length, diameter, and the number of p1/p2 and p3 segmental perforators were determined, and the relationship between the caudal loop and cerebellar tonsil position was also assessed. The distance between the PICA's origin and the cranial nerve XI (CN XI), the buffer length above the CN XI after dissection, the OA length required to complete the OA-p1/p3 PICA bypass, and the p1 and p3 segment diameters were all measured. A bypass training practical scale (TSIO) was used to evaluate the quality of the anastomosis. RESULTS: All specimens underwent OA-p1 PICA end-to-end bypass and had favorable results for the TSIO score, 15 sides underwent OA-p3 PICA end-to-side bypass, and the other bypass protocols were less common. The buffer length above the CN XI after dissection, the distance between the PICA's origin and the CN XI, and the first perforator were all of sufficient length. The direct length of the OA needed to complete the OA-p1 PICA end-to-end bypass was significantly less than the available length and the OA-p3 PICA end-to-side bypass, with the OA matching the p1 segment diameter. The number of p1 perforators was less than that of p3, and the OA diameter was equal to that of the p1 segment. CONCLUSION: OA-p1 PICA end-to-end bypass is a feasible alternative in cases in which p3 segment has high caudal loops or anatomic anomalies.

Medullary branches of the vertebral artery: microsurgical anatomy and clinical significance.

BACKGROUND: Since the medullary arteries are of a great neurologic and neurosurgical significance, the aim was to perform a detailed microanatomic study of these vessels, as well as of the medullary infarctions in a group of patients. METHODS: The arteries of 26 halves of the brain stem were injected with India ink and gelatin, microdissected and measured with an ocular micrometer. Neurologic and magnetic resonance imaging (MRI) examinations were performed in 11 patients. RESULTS: The perforating medullary arteries, averaging 6.7 in number and 0.26 mm in diameter, most often originated from the anterior spinal artery (ASA), and rarely from the vertebral (VA) (38.5%) and the basilar artery (BA) (11.6%). They supplied the medial medullary region. The anterolateral arteries, 4.8 in number and 0.2 mm in size, most often arose from the ASA and PerfAs, and nourished the anterolateral region. The lateral arteries, 2.2 in number and 0.31 mm in diameter, usually originated from the VA and the posterior inferior cerebellar artery (PICA). They supplied the lateral medullary region. The dorsal arteries, which mainly arose from the PICA and the posterior spinal artery (PSA), nourished the dorsal region, including the roof of the 4th ventricle. The anastomotic channels, averaging 0.3 mm in size, were noted in 42.3%. Among the medullary infarctions, the lateral ones were most frequently present (72.8%). CONCLUSION: The obtained anatomic data, which can explain the medullary infarctions symptomatology, are also important in order to avoid damage to the medullary arteries during neurosurgical and neuroradiologic interventions.

Microsurgical anatomical vascular study of the PICA-PICA bypass.

OBJECTIVE: To assess the posterior inferior cerebellar artery (PICA)-PICA bypass possibility. METHODS: Fifteen adult cadaver heads were used for surgical simulation, and the far-lateral approach was used to expose the surgical field. The bilateral PICA course, diameter, and perforators were observed and measured to evaluate the possibility of a PICA-PICA bypass. RESULTS: The PICA-PICA bypass was performed in seven (46.7 %) of the 15 specimens; the procedure was performed easily in three specimens, a little difficult in two, and was difficult in two specimens because of the relationship between the tonsil and the short parallel length of the bilateral tonsillomedullary (p3) segment. In eight (53.3 %) of the 15 specimens, PICA-PICA bypass was not feasible for reasons including 1) the caliber of the bilateral p3 was unmatched for bypass, 2) the distance of bilateral p3 in the midline was > 7 mm, 3) the middle segment of p3 perforating direct arteries limited the buffer length, and 4) single caudal loops. CONCLUSION: The possibility of PICA-PICA bypass was determined by the proximity of the bilateral p3, caliber match, and mobilization of the bilateral caudal loop due to the perforators. The difficulty of the PICA-PICA bypass mainly depends on the relationship between the cerebellar tonsil and the parallel length of the bilateral PICA in the midline.

A posterior inferior cerebellar artery of C2 transverse foramen level origin that entered the spinal canal via the C1/2 intervertebral space demonstrated by computed tomography angiography.

PURPOSE: To describe a case of a posterior inferior cerebellar artery (PICA) of C2 transverse foramen level vertebral artery (VA) origin that entered the spinal canal via the C1/2 intervertebral space. CASE REPORT: A 48-year-old man with posterior neck pain underwent computed tomography (CT) angiography and selective left vertebral angiography. Arterial dissection was found at the distal V2 segment of the left VA on subtracted CT angiography. The left PICA arising from the VA at the level of C2 transverse foramen was identified on CT angiography with bone imaging. This PICA of extracranial origin entered the spinal canal via the C1/2 intervertebral space, just like a PICA of C1/2 level origin. DISCUSSION: The origins of PICAs show several variations. PICAs originating at the extracranial C1/2 level VA are relatively rare, with a reported prevalence of approximately 1%. Our patient had a left PICA arising from the VA at the level of the C2 transverse foramen. No similar cases have been reported in the relevant English-language literature. We speculated that the proximal short segment of the PICA arising from the C1/2 level VA regressed incidentally and that the distal segment of the PICA was supplied by the muscular branch of the VA arising from the level of the C2 transverse foramen. CONCLUSION: We reported the first case of PICA arising from the C2 transverse foramen level VA. CT angiography with bone imaging is useful for identifying a PICA arising from the extracranial VA.

Posterior inferior cerebellar artery originating from the posterior meningeal artery mimicking dural arteriovenous fistula.

PURPOSE: Many variations in the origin of the posterior inferior cerebellar artery (PICA) have been reported. To our knowledge, only one case of a PICA originating from the posterior meningeal artery (PMA) has been reported. METHODS: We describe a case with a PICA that was supplied retrograde from the distal segment of the PMA, mimicking a dural arteriovenous fistula on magnetic resonance angiography (MRA). RESULTS: A 31-year-old man was admitted to our hospital with a sudden occipital headache and nausea. MRA showed a hyperplastic left PMA, continuing to an abnormal vessel that was suspicious for venous drainage. Digital subtraction angiography revealed the left PMA originated from the extradural segment of the vertebral artery and then connected to the left PICA near the torcula. The cortical segment of the PICA flowed retrograde, which appeared as venous reflux on MRA. A second PICA originated from the extradural segment of the left vertebral artery and perfused the tonsillomedullary and televelotonsillar segment of the left PICA territory. CONCLUSION: We present an anatomical variant of the PICA mimicking a dural arteriovenous fistula. Digital subtraction angiography is useful for diagnosis of the cortical segment of the PICA flowing retrograde from the distal segment of the PMA because signal intensity in MRA of retrograde flow tends to decrease and diagnosis may be difficult. During endovascular treatment and open surgery, we should note that ischemic complications may occur due to the potential anastomosing channels between cerebral and dural arteries.

Revisiting the Tentorial Venous Sinuses: Anatomical and Histological Study.

BACKGROUND: Anatomical studies of the tentorial sinuses (TS) are scant, and to our knowledge, histological studies of this structure have not been reported. Therefore, we aim to better elucidate this anatomy. METHODS: In 15 fresh frozen, latex injected, adult cadaveric specimens, the TS were evaluated with microsurgical dissection and histology. RESULTS: The superior layer had a mean thickness of 0.22 mm, and the inferior layer had a mean thickness of 0.26 mm. Two types of TS were identified. Type 1 was a small intrinsic plexiform sinus with no obvious connections to the draining veins with gross examination. Type 2 was a larger tentorial sinus with direct connections to the bridging veins from the cerebral and cerebellar hemispheres. In general, type 1 sinuses were located more medially than type 2 sinuses. The inferior tentorial bridging veins drained directly into the TS along with connections to the straight and transverse sinuses. In 53.3% of specimens, superficial and deep sinuses were seen, with superior and inferior groups draining the cerebrum and cerebellum, respectively. CONCLUSIONS: We identified novel findings for the TS which can be considered surgically and when diagnosing pathology involves these venous sinuses.

Comparison Between the Supracerebellar Infratentorial and Precuneal Interhemispheric, Transtentorial Approaches to the Cerebellomesencephalic Fissure: An Anatomoradiological Study and Illustrative Cases.

BACKGROUND: The dorsal brainstem and cerebellomesencephalic fissure are challenging surgical targets. To afford a preferentially craniocaudal trajectory to this region, the precuneal interhemispheric transtentorial approach (PCIT) has been proposed. OBJECTIVE: To didactically describe and compare exposures and anatomic indications of the supracerebellar infratentorial approach (SCIT) and PCIT to the cerebellomesencephalic fissure. METHODS: Nine formalin-fixed, latex-injected cadaveric head specimens were used to perform a midline SCIT and bilateral PCITs and measure the distance of each approach. Twenty-four formalin-fixed specimens were used to measure the distance from the most posterior cortical bridging vein entering the superior sagittal sinus to the calcarine sulcus and the torcula. Fifty-one magnetic resonance images were reviewed to calculate the angle of each approach. Three illustrative surgical cases were described. RESULTS: Mean distances from the brain or cerebellar surface to the operative target of the PCIT and SCIT were 7.1 cm (range: 5-7.7 cm) and 5.5 cm (range: 3.8-6.2 cm), respectively. The SCIT provided direct access to structures of the quadrigeminal cistern bilaterally. The PCIT provided access from the ipsilateral inferior colliculus to the ipsilateral infratrochlear zone. The PCIT's benefit was the direct access it provided to the cerebellomesencephalic fissure because of its superior to inferior trajectory. CONCLUSION: The PCIT is indicated for unilateral lesions of the cerebellomesencephalic fissure and dorsal brainstem that harbor a craniocaudal long axis and do not have a superior extension beyond the superior colliculi. The SCIT is beneficial for lesions that extend bilaterally, have an anteroposterior long axis, or involve the Galenic complex.

Usefulness of combining CISS and digital subtraction angiography in diagnosis of isolated posterior inferior cerebellar artery dissection.

A 63-year-old man was admitted to our stroke center with brain infarction in the left posterior inferior cerebellar artery (PICA) territory. The initial MRI showed no findings suggestive of arterial dissection, and post-discharge MRI showed no temporal changes. Digital subtraction angiography (DSA) revealed vasodilation of the proximal portion of the PICA but it was uncertain whether dissection was present. Discrepancy between the outer contour seen on constructive interference in steady state (CISS) MRI and the inner contour seen on DSA suggested the presence of intramural hematoma. The patient was diagnosed with brain infarction caused by isolated PICA dissection (iPICAD). Imaging evaluation of combined CISS and DSA may be particularly useful for identification of small iPICAD lesions.