Chordae Willisii of the dural sinuses: an anatomical study using magnetic resonance imaging.

PURPOSE: The chordae Willisii (CWs), trabecular projections into the lumen of the dural sinuses, are not well understood. We aimed to explore them using magnetic resonance imaging (MRI). METHODS: Eighty-five patients underwent volumetric contrast-enhanced MRI, while another 30 underwent a fluid-attenuated inversion recovery (FLAIR) sequence in the coronal section. RESULTS: The CWs were detected as linear filling defects lying in the dural sinuses, adjacent to the surrounding dura mater. They were found in the superior sagittal sinus (SSS) in 68.2% of the patients, most frequently in the middle third, with laminar appearance. In 27.1% of the patients, the CWs divided the SSS lumen into separate channels. The CWs were identified in the transverse sinus, transverse-sigmoid sinus junctional area and sigmoid sinus, and straight sinus in 54.1, 47.1, and 8.2%, respectively. On the FLAIR images, dural septi partially dividing the SSS lumen were identified in all patients. In addition, in 73.3% of the patients, fine linear structures were observed in the lumen with inconstant arrangements. CONCLUSIONS: The CWs may be constant structures distributed over the lumen of the intracranial dural sinuses. Contrast-enhanced MRI may be useful for detecting laminar CWs. The FLAIR sequence may be advantageous for delineating the dural septi projecting into the lumen of the dural sinuses.

Diameters of the optic sheath and superior ophthalmic vein can expand and contract at positional changes: a magnetic resonance imaging study.

PURPOSE: This study aimed to explore the diameters of the optic sheath (OSD) and superior ophthalmic vein (SOVD) in response to positional changes using magnetic resonance imaging (MRI). MATERIALS AND METHODS: Fifty adult outpatients who presented to the hospital underwent thin-slice coronal T2-weighted MRI in the supine position followed by the prone position. RESULTS: The OS and SOV were well delineated in all the patients. The OSD in the anterior orbit was measured in the supine and prone positions on both sides. In addition, the SOVD in the anterior and posterior orbits was measured in the supine and prone positions on both sides. The OSD demonstrated an increase on both sides in 100% of the cases. The SOVD demonstrated an increase on both sides in 94% of the cases, whereas the remaining 6% demonstrated a decrease. The OSD measured at the anterior orbit and the SOVD at the anterior and posterior orbits significantly increased on both sides with positional changes from the supine to the prone position. CONCLUSION: OSD and SOVD may expand and contract in response to alterations in the intracranial pressure and venous flow patterns. MRI examination in the supine position combined with positional changes can help to better understand the OS and SOV as dynamic structures.

Spinal endodermal cyst undergoing malignant transformation and marked elevation of serum carbohydrate 19-9 level.

Endodermal cyst (EC) is a benign tumor that can arise along the craniospinal axis. Infrequently, ECs undergo malignant transformation. A 43-year-old man presented with numbness in the right arm, leg and occipitalgia. MRI revealed a multicystic, intradural extramedullary tumor at C2 with enhancement along the ventral surface of the spinal cord. Blood test showed an abnormal increase in serum carbohydrate antigen 19-9 (CA 19-9) level. Systemic positron emission tomography-computed tomography was normal. He underwent total tumor resection and was diagnosed with EC. He developed double vision, hearing loss, and swallowing difficulty on postoperative day 70. Cerebral MRI revealed marked extensions of leptomeningeal dissemination. The serum CA 19-9 level increased continuously and finally reached 1515.0 U/ml. He died of respiratory failure on day 108. An autopsy did not reveal abnormalities in the abdominal and chest organs. On microscopic examination, the post-mortem specimen revealed adenocarcinoma. Immunohistochemically, both the surgical and autopsy specimens were positive for CA 19-9. Spinal ECs may lead to malignant transformation with leptomeningeal dissemination that causes abnormal elevation of serum CA 19-9 levels.

Delineation of the lacrimal vein: a magnetic resonance imaging study.

PURPOSE: To our knowledge, anatomical knowledge about the lacrimal vein (LV) is missed. Therefore, this retrospective study aimed to explore them using magnetic resonance imaging (MRI). MATERIALS AND METHODS: Eighty-one patients who underwent contrast-enhanced MRI and three donated bodies to science were enrolled. RESULTS: On the sagittal images, the measured mean right long (LD) and short diameters (SD) of the lacrimal gland (LG) were 17.3 ± 2.4 mm and 13.7 ± 2.1 mm, while the left LD and SD were 17.0 ± 2.6 mm and 13.6 ± 2.6 mm, respectively. Laterality or sex differences were not found in the LD and SD groups. In addition, no specific age range was associated with a significantly longer LD or SD. LVs were identified in 94% of axial images. Their course was classified into as follows: three types: connecting to the superolateral cavernous sinus (CS), to the superior ophthalmic vein (SOV), and the diploic channels of the greater wing of the sphenoid bone (DCGW). The CS type was the most frequently identified, followed by the SOV and DCGW types. In dissected specimens, the LVs consistently coursed between the posterior margin of the LG and the superolateral part of the CS, above the upper margin of the lateral rectus muscle. CONCLUSIONS: The LV may consistently emerge from the upper posterior margin of the LG. It commonly pours into the SOV or superolateral part of the CS.

Delineation of intermammillary relationships using magnetic resonance imaging.

PURPOSE: No study has investigated intermammillary relationships using neuroimaging modalities. This study aimed to explore them using magnetic resonance imaging (MRI). MATERIALS AND METHODS: We enrolled 72 patients who underwent conventional MRI examinations, followed by constructive interference steady-state sequence in the coronal plane. The intermammillary distances (IMDs) were measured at the uppermost level of the intermammillary gap (IMDupp) and the lowest level (IMDlow) of the mammillary bodies (MBs). RESULTS: MBs with varying morphologies were consistently delineated. The appearance of both MBs could be classified into four patterns based on the size and relative levels, with the symmetrical type being the most common. Intermammillary relationships exhibited five patterns. In 69%, the IMDupp was discernible and measured 0.7 ± 0.4 mm, while it was not discernible in 31% due to the presence of intermammillary connection and adhesion. The age distribution did not differ between populations with and without discernible IMDupp. The IMDlow was measured 4.4 ± 0.9 mm. Although the IMDlow was not significantly different between both sexes; it was longer in subjects in their 70s. CONCLUSIONS: Intermammillary relationships show variable morphologies with gaps formed between both MBs. The IMDlow may become more evident in association with age-related increase in the width of the third ventricle and atrophy of the MBs.

Do the mammillary bodies atrophy with aging? A magnetic resonance imaging study.

PURPOSE: This retrospective study aimed to explore age-related atrophy of the mammillary bodies (MBs) based on their temporal change using magnetic resonance imaging (MRI). MATERIALS AND METHODS: The study included 30 adult outpatients who presented to the hospital and were followed for more than 100 months with annual MRIs. The bi-ventricular width (BVW), third ventricle width (TVW), and bi-mammillary dimension (BMD) were measured on axial T2-weighted imaging and analyzed. RESULTS: The 30 patients comprised 1 in their 40s, 5 in their 50s, 6 in their 60s, 11 in their 70s, 5 in their 80s, and 2 in their 90s. The MBs were consistently detected with left-to-right symmetry. The mean BVW was 32 ± 2.2 mm on the initial (BVW1) and 32 ± 2.4 mm on the last (BVW2) MRI. The mean TVW was 7.0 ± 2.3 mm on the initial (TVW1) and 7.6 ± 2.7 mm on the last (TVW2) MRI. Furthermore, the mean BMD was 9.9 ± 1.3 mm on the initial (BMD1) and 10 ± 1.3 mm on the last (BMD2) MRI. Statistically, no age ranges had a large dimension for BVW1, BVW2, TVW1, TVW2, BMD1, or BMD2. Changes between TVW1 and TVW2 were significantly different in the patients in their 80s; changes between BMD1 and BMD2 were not different for any age range or between sexes. CONCLUSIONS: Aging alone does not seem to promote MB atrophy. In healthy brains, the MBs may be stationary structures throughout life.

Delineation of the central retinal artery using computed tomography: a pilot study.

PURPOSE: The prospective study aimed to examine the central retinal artery (CRA) using computed tomography (CT). MATERIALS AND METHODS: Seventy adult outpatients comprising 32 men and 38 women, at a mean age of 60.6 ± 13.3 years, were enrolled in the study. The patients underwent contrast-enhanced CT. The scan timing was set to start 5.0 s after the circle of Willis began to be delineated. RESULTS: The ophthalmic arteries (OphAs) were comfortably delineated in all. In 97% of the patients, the CRA was delineated from the original site on the OphA to a more distal segment coursing on the optic sheath. Unilateral and bilateral CRA delineations were observed in 44% and 53% of cases, respectively. The delineated CRAs demonstrated highly variable morphologies in terms of the course and length on the optic sheath. In addition, the distance between the original site of the CRA and the posterior limit of the bulb was measured. The mean distance was 18.6 ± 5.0 mm on the right and 17.8 ± 4.3 mm on the left, respectively. No significant right-to-left differences in the measurements (p > 0.05) were observed. CONCLUSIONS: If optimal scan timing is adopted, the CRA segments coursing on the optic sheath can be delineated using contrast-enhanced CT. CT may be a useful diagnostic modality for the CRAs and associated pathological conditions.

Fluid-Filled Dehiscences in the Anterior Cranial Fossa Floor: A Magnetic Resonance Imaging Study.

OBJECTIVE: To date, only limited information regarding the anterior cranial fossa floor (AFF) and the appearance of sites of dehiscence and potential channels has been available. We aimed to evaluate this region with thin section magnetic resonance imaging (MRI). PATIENTS AND METHODS: A total of 65 patients underwent thin-sliced coronal T2-weighted MRI. The AFF was divided into 3 parts for analysis: the anterior, middle, and posterior. RESULTS: Dehiscences were identified in 84.6% of 65 patients with apparently transmitting channels. In 49.2% of the patients, the dehiscences were located in the anterior part, whereas they were located in the middle and posterior parts in 52.3% and 12.3%, respectively. The morphology and number of these dehiscences were highly variable. In 12.3%, channels in the dehiscences were distributed extradural. Statistically, dehiscences were more frequently identified on the left side in any part of the AFF. CONCLUSIONS: With thin-sliced, coronal T2-weighted MRI, dehiscences were frequently identified in the anterior two-thirds of the AFF. Further study is warranted to determine the role of AFF channels and dehiscences, including possibly for cerebrospinal fluid drainage.

Central retinal artery delineation using magnetic resonance imaging.

PURPOSE: Few studies have explored the central retinal artery (CRA) using neuroimaging. Our study aimed to explore this using magnetic resonance imaging (MRI). METHODS: A total of 81 patients with intact orbital structures and visual function underwent thin-slice contrast MRI. RESULTS: The identified CRAs showed highly variable morphologies on both axial and sagittal images. On the axial images, the CRAs were detected in the right orbit in 11.1% and in the left orbit in 19.8%. The distance between the site of CRA branching from the ophthalmic artery to the posterior limit of the bulb was 18.8 ± 3.9 mm (12.8-24.6 mm) on the right and 18.9 ± 3.3 mm (14.6-26.7 mm) on the left. On the sagittal images, CRAs were detected on the right in 76.5% and on the left in 85.2%. The distance between the CRA branching site and the posterior limit of the bulb was 20.4 ± 3.8 mm (14.2-28.2 mm) on the right and 19.2 ± 3.7 mm (11.3-27.1 mm) on the left. CONCLUSIONS: Thin-sliced, contrast sagittal MRI can be used to explore the proximal part of the CRA. In particular, serial sagittal imaging may be useful for detecting the CRAs and their relationship with relevant structures.

Correlation of the external occipital protuberance with venous sinuses: a magnetic resonance imaging study.

PURPOSE: To date, no study has explored the external occipital protuberance (EOP) using neuroimaging modalities. This study aims to characterize them using magnetic resonance imaging (MRI). METHODS: A total of 96 patients underwent thin-sliced, post-contrast MRI. The sagittal images were analyzed. RESULTS: In 97%, the EOPs were delineated as a focal external protrusion of the midline region of the occiput with varying morphologies. In 89% of 93 patients with identifiable EOPs, parts of the intracranial dural sinuses were found to lie just below the inion, the most prominent point of the EOP. The most frequently targeted dural sinus was the confluence of sinuses that was found in 57%, followed by the superior sagittal sinus. In 16%, a bony foramen and transmitting vessel were detected in the EOP, connecting between the diploic channels and the subcutaneous veins. Furthermore, in 33%, bony foramina and transmitting venous structures were identified in the region just below the EOPs, connecting between the diploic channels and the subcutaneous veins. CONCLUSIONS: The intracranial dural venous sinus is located just below the EOP with a high probability. Most bony foramina in the EOP and midline suboccipital region may transmit veinous structures connecting to the diploic channel.

Bilateral vertebral artery fenestrations in the craniocervical junction region: the clinical role of 3D computed tomography angiography.

Fenestration of the vertebral artery (FVA) is a rare occurrence that comprises only 2% of fenestrations formed in the intracranial arteries. Herein, we report a unique case of bilateral FVA in the craniocervical junction (CCJ) region using conventional magnetic resonance angiography (MRA) and three-dimensional computed tomography angiography (3D-CTA). Compared to MRA, 3D-CTA was more sensitive in delineating the FVAs located in the region. Furthermore, it effectively depicted the relationships between the VAs and surrounding bony structures. The clinical implications of FVAs can be better understood in relation to the surrounding bony structures. 3D-CTA is mandatory when performing endovascular and open surgical interventions in and around the VA segments in the CCJ region.

Hyperintense areas in the cisternal segments of the cranial nerves: a magnetic resonance imaging study.

PURPOSE: The study aimed to explore hyperintense areas in the cisternal segments of the cranial nerves using magnetic resonance imaging (MRI). METHODS: Seventy outpatients underwent thin-sliced, coronal constructive interference steady-state (CISS) sequence and sagittal T2-weighted MRI following conventional MRI examination. RESULTS: With the coronal CISS sequence, hyperintense areas were located in the central parts of the olfactory bulbs in 65.7% of patients. For the intracranial optic nerve and optic chiasm, hyperintense areas were detected in 98.6% of the CISS sequences and 100% of the T2-weighted images. In the optic tract, hyperintense areas were detected in 51.4% of cases. In 35% of the patients who underwent the CISS sequence, the intracranial optic nerves were considerably compressed by the internal carotid and anterior cerebral arteries, with hyperintense areas similar to those in patients without vascular compression. Hyperintense areas of the cisternal segments of the oculomotor nerve and trigeminal root were identified in 52.9% and 87.1% of the patients, respectively. CONCLUSIONS: The hyperintense areas found within the cisternal segments of the cranial nerves delineated on the coronal CISS sequence and sagittal T2-weighted imaging may indicate the intracranial part of the glymphatic pathway through the cranial nerves. The cranial nerves may function as part of the glymphatic pathway.

"Hammock" suspending the superior ophthalmic vein: a magnetic resonance imaging study.

PURPOSE: The present study aimed to explore the hammock-like structure suspending the superior ophthalmic vein (SOV) using magnetic resonance imaging (MRI). METHODS: Following conventional MRI examination, 93 outpatients underwent thin-sliced, coronal T2-weighted and contrast imaging of the orbit. RESULTS: SOVs were consistently detected in all 93 patients. In 90.3% of patients, a hammock-like structure suspending the SOV was identified, which was present on both sides in 64.5% of patients. The structure was frequently located in the anterior and middle thirds of the retrobulbar orbit, suspended from the superolateral corner of the orbital walls. The medial edge of the hammocks did not reach the orbital walls; therefore, they partially encased the SOV. The morphology of the hammock was highly variable between patients, although none were tethered to the extraocular muscles. In addition, a septal band connecting the hammock and optic sheath was identified in 36.6% of patients, most frequently located in the posterior third of the retrobulbar orbit. CONCLUSIONS: The hammock suspending the SOV and the septal band connecting the hammock and optic sheath may be structures that loosely anchor the SOV to the orbital fat to maintain a constant SOV flow, in addition to preventing excessive bends and obstructions.

Oculomotor nerve segment between proximal posterior and superior cerebellar arteries: an MRI study.

PURPOSE: No study has documented the oculomotor nerve (OMN) segment lying between the posterior cerebral (PCA) and superior cerebellar (SCA) arteries adjacent to the brainstem. The present study aimed to characterize it. METHODS: A total of 71 patients underwent thin-sliced, sagittal T2-weighted magnetic resonance imaging for analysis. RESULTS: The OMN segments lying between the PCA and SCA were identified in all patients. The OMN segment in relation to the PCA and SCA was classified into five types. Of them, the PCA-OMN contact type was the most frequent and found in 35.2% of 71 sides on the right and 39.4% on the left. Also, the PCA-OMN compression type was identified in 12.7% on the right and 15.5% on the left. In these types, the mean distance between the brainstem and contact/compression sites were measured 4.4 ± 2.3 mm on the right and 4.4 ± 1.6 mm on the left. In more than forty percent, the sites were located at the level of the pontomesencephalic junction. CONCLUSIONS: The OMN may be frequently in contact with the PCA near the brainstem. The site located more distal than the central-peripheral myelin junction of the OMN can attribute to a low frequency of neurovascular compression syndrome of the nerve.

Root exit zone of the trochlear nerve on the dorsal brainstem: an MRI study.

PURPOSE: To date, no study has explored the root exit zone of the trochlear nerve (TroN) on the dorsal brainstem; therefore, we aimed to characterize the location using magnetic resonance imaging (MRI). METHODS: A total of 85 patients underwent thin-slice axial T2-weighted MRI. RESULTS: TroN was identified in 91% of 85 patients, 60 (71%) on the right side, and 67 (79%) on the left. The distances between the apex of the inferior colliculus and the original site of TroN on the dorsal brainstem were variable, with mean values of 2.4 ± 1.8 mm (range 0-8 mm) on the right and 2.2 ± 1.7 mm (range 0-5 mm) on the left. Most of the root exit zones were distributed within 0-5 mm below the apex of the inferior colliculus. In addition, the distances between the midline and the root exit zones of the TroN were variable, with mean values of 4.4 ± 1.4 mm (range 1.9-7.5 mm) on the right and 4.6 ± 1.6 mm (range 1.1-7.8 mm) on the left. Most of the root exit zones were located within 1-7 mm range lateral to the midline. CONCLUSIONS: The root exit zone of the TroN may be mostly located in a small square area measuring 8 mm × 8 mm, lying at and below the apex of the inferior colliculus. The TroN may arise from any site in the square area, and significant attention is necessary when performing surgical maneuvers in and around it.

Meckel Cave: An Anatomical Study Using Magnetic Resonance Imaging.

OBJECTIVE: To our knowledge, few studies have investigated anatomy of the Meckel cave with neuroimaging modalities. The present study aimed to characterize it using magnetic resonance imaging (MRI). PATIENTS AND METHODS: Following conventional MRI examination, a total of 101 patients underwent T2-weighted imaging in thin-sliced coronal and sagittal sections, and 11 patients underwent constructive interference steady-state sequences in thin-sliced sagittal sections. Moreover, 3 injected cadaver heads were dissected. RESULTS: In the cadaver specimens, the size and extent of the cerebrospinal fluid-filled space between the Gasserian ganglion and surrounding arachnoids were difficult to define. On the T2-weighted imaging, the Meckel cave was delineated with variable morphologies and left-right asymmetry. On the sagittal images, the shape of the Meckel cave could be classified into 3 different types, bulbous, oval, and flat, with the oval being the most frequent that comprised 60%. Furthermore, on the sagittal constructive interference steady-state images, parts of the trigeminal nerve distributed in the Meckel cave were delineated in all patients. The ophthalmic, maxillary, and mandibular divisions were clearly distinguished on both sides. CONCLUSIONS: The Meckel cave is a structure characterized by diverse morphologies and left-right asymmetry. Thin-sliced T2-weighted imaging is useful for exploring the anatomy of the Meckel cave.

Emissary Foramina of the External Occipital Protuberance: A Magnetic Resonance Imaging Study.

OBJECTIVE: The posterior interparietal region is known to be a distinct area of the skull, predisposing to a variety of bony variants and congenital anomalies. The bony canals in this region have not yet been explored in detail. This study aimed to characterize them. PATIENTS AND METHODS: Overall, 82 patients underwent thin-slice contrast magnetic resonance imaging. Coronal and sagittal images were used for the analysis. RESULTS: At the rostral limit of the posterior interparietal region, the parietal foramen (PF) and transmitting emissary vessels were identified in 84% of cases, mostly delineated as single channels. They were located in the left parasagittal region (PS) in 26%, lateral to the left PS in 33%, right PS in 40%, lateral to the right PS in 12%, and midline in 16% of the cases. In 4% of the cases, the PF presented an obstruction around the outer opening. In the more caudal part of the posterior interparietal region, 51% of the patients presented with fine bony canals and transmitting emissary vessels, lying in the midline and parasagittal levels. CONCLUSIONS: The frequency of PFs may be underestimated for superficially hidden outer openings of the canals. The midline posterior interparietal region may present fine bony canals for transmitting emissary vessels that function complementarily with PFs.

The Arcuate Eminence and Superior Semicircular Canal: Magnetic Resonance Imaging Study.

OBJECTIVE: The present study aimed to explore the relationship between the arcuate eminence (AE) and superior semicircular canal (SSC) using the constructive interference steady-state (CISS) sequence. PATIENTS AND METHODS: After conventional magnetic resonance imaging, a total of 71 patients underwent the CISS sequence in thin-sliced coronal sections. RESULTS: In all patients, the SSC was delineated on both sides. In contrast, the AE was identified only in 29 of 71 patients (40.8%) on both sides, varying in shape and relative location to the SSC in the mediolateral dimension. The shortest distance between the highest point of the SSC and middle fossa floor was 1.3 ± 1.1 mm on the right side and 1.3 ± 0.9 mm on the left with considerable variability. A dehiscent SSC with a distance less than 0.2 mm was found in 11.3% of 142 sides. On 22 sides (15.5%), the site on the middle fossa floor, reaching the SSC with the shortest distance (reference point) corresponded to the apex of the AE, equally on the right and left. On 36 sides (25.4%), the distance between the reference point and the apex of the AE was measured as 3.0 ± 1.1 mm on the 18 right sides and 3.7 ± 1.6 mm on the 18 left sides. CONCLUSIONS: The relationship between AE and SSC is highly variable. Arcuate eminence was not a reliable landmark of the SSC. High-resolution CISS sequence is useful for exploring these structures.

Subependymal hyperintense layer on CISS sequence: An MRI study.

PURPOSE: The present study aimed to explore the subependymal layers overlying the cerebral ventricles using magnetic resonance imaging. METHODS: A total of 69 outpatients underwent constructive interference in steady-state (CISS) sequence in thin-sliced, coronal, and sagittal sections. RESULTS: The subependymal layers were delineated as linear hyperintensities, coursing along the outer margins of the ventricular walls. On coronal images, the hyperintensities surrounding the anterior horn of the lateral ventricle were identified in 97% of patients, while those of the third ventricle were identified in 96% of patients. In the trigone and posterior horn of the lateral ventricle, the hyperintensities were delineated in all patients. On sagittal images, subependymal hyperintensities were identified in all. At the level of the anterior horn and third ventricle, the subependymal hyperintensities were found to communicate with the Virchow-Robin spaces (VRSs) in 68% and 65% of patients, respectively. At the level of the trigone and posterior horn of the lateral ventricle, the VRSs communicated with the subependymal hyperintensities in 83% of patients. CONCLUSIONS: Subependymal hyperintensity may represent an inflow passage of the VRSs that jointly contribute to efficient transependymal migration of the interstitial fluid into the ventricular cerebrospinal fluid.

Bridging veins of the cerebellum: a magnetic resonance imaging study.

PURPOSE: To date, no study has yet explored the bridging veins (BVs) of the cerebellum using neuroimaging modalities. Therefore, this study aimed to characterize them using magnetic resonance imaging (MRI). METHODS: A total of 90 patients with intact cerebellar hemispheres and intracranial dural sinuses underwent thin-sliced, contrast-enhanced MRI. RESULTS: The BVs were classified into six routes based on the draining pattern into the dural sinuses. The superior vermian vein emptying into the straight sinus was delineated in 100% of the patients. The inferior vermian vein emptying into the confluence of the sinuses was identified in 66.7% of the patients. The inferior hemispheric and cerebellar cortical veins emptying into the transverse sinus were identified in 54.4% and 26.7% of the patients, respectively. The inferior vermian and cerebellar cortical veins emptying into the straight sinus were identified in 77.8% and 12.2% of the patients, respectively. The cerebellar cortical vein emptying into the tentorial sinus was identified in 83.3% of the patients; it was delineated on 54 sides with an average number per right hemisphere of 1.9 and 63 sides with an average number per left hemisphere of 2. The pontine-trigeminal and anterior hemispheric veins emptying into the superior petrosal sinus were identified in 42.2% of the patients. CONCLUSIONS: The BVs of the cerebellum can be classified into six distinct routes. Radiological classification may be useful for understanding the drainage pattern of the cerebellum.