Absence of the torcular, review of venous sinus anatomy, and the simplified dural sinus classification.

BACKGROUND: Classically, the torcular Herophili is described as the symmetric junction between the superior sagittal sinus (SSS), transverse sinuses (TSs), and straight sinus (SS). However, finding this pattern in practice is not standard. Anatomical variations are common, and different drainage patterns should be expected. Existing literature proposes highly detailed descriptions and classifications of this region. Still, a simplified and practical categorization is not available. METHODS: We present an anatomical finding of the torcular Herophili discovered on a cadaveric dissection. Then, we conducted a retrospective study examining the 100 most recent cranial magnetic resonance venographies (MRVs) from the Mayo Clinic, labeling them with a new proposed dural sinus classification system. Images were initially classified by two authors and further validated by a board-certified neurosurgeon and a board-certified neuroradiologist from our institution. To measure consistency in image identification, two additional international neurosurgeons were asked to classify a subset of the same MRV images, and their answers were compared. RESULTS: Of the MRV cohort, 33 patients were male and 67 were female. Their ages ranged from 18 to 86 years, with a mean of 47.35 years and a median of 49 years. Upon examination, 53 patients presented as confluent (53%), 9 as SSS divergent (9%), 25 as SS divergent (25%), 11 as circular (11%), and 2 as trifurcated (2%). The inter-rater reliability ranked very good; agreement between the two neurosurgeons was 83% (κ = 0.830, p < 0.0005). CONCLUSION: The confluence of the venous sinuses is a highly variable anatomical area that is rarely evaluated with neuroimaging before surgery. The classic textbook configuration is not the rule. Using a simplified classification system may increase awareness and hopefully patient safety by preparing the physician for anatomical variations that they will encounter in a surgical or clinical scenario.

Chordae Willisii Within the Transverse Sinus: Morphologic Study.

OBJECTIVE: Some have suggested that trabeculae within the transverse sinuses (chordae Willisii) might restrict flow and potentially contribute to thrombus organization. In addition, these structures might be encountered with endovascular procedures within the transverse sinus and are now readily seen on imaging. Therefore as anatomic studies of these structures are scant, the current study aimed to better elucidate these structures within the transverse sinus via a morphologic study in cadavers. METHODS: Thirty fresh-frozen, cadaveric transverse sinuses were dissected, and their detailed morphology was recorded. Classification schemes were applied based on the anatomy and orientation of each chordae. RESULTS: Chordae were found on 70% of sides and were statistically more likely to be found on right sides (86.6%) (P < 0.01). Three types and 3 classes of chordae were identified. There was a statistically significant difference between sides regarding type of chordae (P = 0.02). CONCLUSIONS: To date, a comprehensive anatomic evaluation of the intraluminal chordae of the transverse sinuses has been lacking. Knowledge of these bands is also essential to those performing endovascular procedures of the dural venous sinuses and for those interpreting imaging of these structures.

Individual variations of the superior petrosal vein complex and their microsurgical relevance in 50 cases of trigeminal microvascular decompression.

BACKGROUND: We investigated the understudied anatomical variations of the superior petrosal vein (SPV) complex (SPVC), which may play some role in dictating the individual complication risk following SPVC injury. METHODS: Microvascular decompressions of the trigeminal nerve between September 2012 and July 2016. All operations utilized an SPVC preserving technique. Preoperative balanced fast field echo (bFFE) magnetic resonance imaging, or equivalent sequences, and operative videos were studied for individual SPVC anatomical features. RESULTS: Applied imaging and operative SPVC anatomy were described for fifty patients (mean age, 67.18 years; female sex and right-sided operations, 58% each). An SPVC component was sacrificed intentionally in 6 and unintentionally in only 7 cases. Twenty-nine different individual variations were observed; 80% of SPVCs had either 2 SPVs with 3 or 1 SPV with 2, 3, or 4 direct tributaries. Most SPVCs had 1 SPV (64%) and 2 SPVs (32%). The SPV drainage point into the superior petrosal sinus was predominantly between the internal auditory meatus and Meckel cave (85.7% of cases). The vein of the cerebellopontine fissure was the most frequent direct tributary (86%), followed by the pontotrigeminal vein in 80% of SPVCs. Petrosal-galenic anastomosis was detected in at least 38% of cases. At least 1 SPV in 54% of the cases and at least 1 direct tributary in 90% disturbed the operative field. The tributaries were more commonly sacrificed. CONCLUSIONS: The extensive anatomical variation of SPVC is depicted. Most SPVCs fall into 4 common general configurations and can usually be preserved. BFFE or equivalent sequences remarkably facilitated the intraoperative understanding of the individual SPVC in most cases.

Preoperative Exposure of Sigmoid Sinus Trajectory in Posterolateral Cranial Base Approaches Using a New Landmark Through a Neurosurgical Perspective.

The location of burr holes in posterolateral cranial base approaches should be appropriate to provide an adequate operative field, and surgical freedom is crucial for bone window opening. The aim of this study was to search for more convenient and easily detectable landmarks in comparison with current landmarks in posterolateral cranial base surgery. Twenty 3-dimensional reconstructed head and neck computed tomography angiography images (group 1) and 20 cadaver heads (group 2) were evaluated. An imaginary line connecting the angle of the mandible and the mastoid tip was extended upward. A second line passing through the lateral edge of the zygomatic arch was also extended posteriorly. The authors examined if the first line met with the sigmoid sinus throughout its course and determined the location of the intersection point of these 2 lines relative to the sigmoid-transverse sinus junction. The intersection point did not correspond to the sinus region in 3 images from group 1 and 4 specimens from group 2. The matching of the mandibula-mastoid line trajectory with the sigmoid sinus course was unacceptable in 4 images and 5 cadavers. For venous anatomy preservation and anatomic skull base fossa orientation during posterolateral cranial base approaches, upward extension of the mandibula-mastoid line can be a proper landmark for surgical planning in this region. The authors' proposed superficial anatomical line and intersection point over the skull could be used as a reliable indicator for the external projection of the sigmoid sinus and an appropriate initial burr-hole location.

Microsurgical anatomy of the superior sagittal sinus and draining veins.

BACKGROUND: The superior sagittal sinus and the draining cerebral veins are often encountered during the surgery for parasagittal and falx meningiomas and during the interhemisperic transcallosal approaches. A knowledge about the variations from the normally described anatomy helps in anticipating and avoiding problems related to these structures during surgery. AIM: The normal variations in the disposition of the superior sagittal sinus and the number and direction of the draining veins in the Indian population have been studied. SETTINGS AND DESIGN: This is an anatomical study in the fresh cadavers. MATERIALS AND METHODS: Sixty fresh cadavers were examined in the autopsy theatre of the Forensic Medicine Department of the Hospital between March 2011 and February 2013. STATISTICAL ANALYSIS USED: Epi-Info, MS-Excel, and the Statistical Package for the Social Sciences (SPSS) were used for data analysis. RESULTS: The position of the superior sagittal sinus was variable and was up to within 1cm on either side of the sagittal suture. The origin of the superior sagittal sinus varied from the level of foramen caecum to a little posterior from the foramen caecum. The total length of the superior sagittal sagitttal sinus varied from 321 mm to 357 mm (average length 338.77mm); vertical compartments of the sinus were found in three-fourth of the cases studied. Tributaries were found in the herringbone pattern and varied from 13 to 19 on the right and 14 to 19 on the left. The Rolandic vein was the largest draining vein in most of the cases. The superior sagittal sinus drained predominantly to the right transverse sinus in three-fourth of the cases studied. The position of the torcula was variable; often towards the right side and at a higher level. The central sulcus was 49.93 mm posterior to the coronal suture and 130.78 mm anterior to the lambdoid suture. CONCLUSIONS: This is the first study of its kind in Indian population studying the anatomical variations in the anatomy of the superior sagittal sinus that may have a significant bearing on the neurosurgical approaches adopted.

Muscle Insertion Line as a Simple Landmark To Identify the Transverse Sinus When Neuronavigation Is Unavailable.

OBJECTIVE: Skull opening in occipital and suboccipital regions might be associated with risk of damage to the transverse venous sinus and the confluence of sinuses. We analyze the value of magnetic resonance (MR) imaging in localizing the venous sinuses in relation to the superior muscle insertion line (MIL) on the occipital bone. METHODS: We retrospectively analyzed head MR images of 100 consecutive patients imaged for any reason from 1 January 2013. All MR images were interpreted by a radiologist (R.K.). The superior MIL was identified at the midline and on both midpupillar lines, which represent the most frequent sites of skin incision and craniotomy (median and lateral suboccipital craniotomy, respectively). RESULTS: Patients comprised 56 women (56%) and 44 men (44%). Their mean age was 54 (range 18-84) years. The muscles of the posterior skull were readily visible and clearly identified in both T1 and T2 images of all patients. Identification of the insertion zone and its relation to the venous structures was most readily made in the sagittal plane. CONCLUSION: We found that the upper muscle insertion line on occipital bone corresponds to the underlying venous sinus and can be used as a reliable anatomic landmark. We identified it in 100% of preoperative MR images of heads with an intact occiput.

Morphologic Study of Positional Relationship Between Transverse-Sigmoid Sinus and Extracranial Bony Landmarks With Reconstructed Computed Tomographic Image.

OBJECTIVE: By using the line between the lowest point of the mastoid process and the external occipital protuberance as landmarks, to locate the projection of the transverse-sigmoid sinus (TSS) on the skull surface using three-dimensional reconstruction technique, to provide morphological basis for avoiding TSS injuries during surgeries. METHODS: A total of 120 volunteers underwent computed tomography scan, and computed tomography reconstruction was used to reconstruct the 3D model of the skull for structural landmark and measurement. The line between the most prominent point (A) of external occipital protuberance and the lowest point (B) of mastoid process was used as the landmark to depict distance between the TSS sulcus and the landmarks, as well as the width of the TSS sulcus. RESULTS: The widths of the transverse sinus sulcus, denoted as d, at its central landmark J were measured to be significantly different between the right and left sides (t = 6.291, P < 0.05); no statistically significant difference was found in the measurements of indicators including h1, h2, h3, h4, h5, h6, h7, h8, d1, α, s1, s2, s3, s4, s5, s6 between the right and left sides (P > 0.05), or between the males and females (P > 0.05). CONCLUSIONS: These above-mentioned results can help to locate the projection of the TSS sulcus on the skull surface accurately, which is simple and convenient in guiding the surgeons to protect the TSS during surgeries.

Localization of Anterosuperior Point of Transverse-sigmoid Sinus Junction Using a Reference Coordinate System on Lateral Skull Surface.

BACKGROUND: During craniotomies using the transpetrosal-presigmoid approach, exposure of the sigmoid sinus remains an essential but hazardous step. In such procedures, accurate localization of the anterosuperior point of the transverse-sigmoid sinus junction (ASTS) is very important for reducing surgical morbidity. This study aimed to create an accurate and practical method for identifying the ASTS. METHODS: On the lateral surfaces of 40 adult skulls (19 male skulls and 21 female skulls), a rectangular coordinate system was defined to measure the x and y coordinates of two points: the ASTS and the squamosal-parietomastoid suture junction (SP). With the coordinate system, the distribution characteristics of the ASTS were statistically analyzed and the differences between the ASTS and SP were investigated. RESULTS: For ASTS-x, significant differences were found in different sides (P = 0.020); the ASTS-x in male skulls was significantly higher on the right side (P = 0.017); there was no significant difference between the sides in female skulls. There were no significant differences in gender or interaction of gender and side for ASTS-x, and for ASTS-y, there were no significant differences in side, gender, or interaction of gender and side. For both sides combined, the mean ASTS-x was significantly higher than the mean SP-x (P = 0.003) and the mean ASTS-y was significantly higher than the mean SP-y (P = 0.011). CONCLUSIONS: This reference coordinate system may be an accurate and practical method for identifying the ASTS during presigmoid craniotomy. The SP might be difficult to find during presigmoid craniotomy and, therefore, it is not always a reliable landmark for defining the ASTS.

Anatomical Variations of the Transverse-Sigmoid Sinus Junction: Implications for Endovascular Treatment of Idiopathic Intracranial Hypertension.

Venous sinus pathology can result in multiple pathological diseases, including idiopathic intracranial hypertension (IIH). There remains a paucity of information on anatomical luminal variations of the major venous sinuses which may contribute to the etiology of certain disease states. Thirty-six transverse and sigmoid sinuses were removed following dissection of 19 unfixed cadaveric heads. Sinuses were opened longitudinally to study luminal variations. A semiquantitative classification system was developed to assess septations and blind pouches. Seventy-nine percent of cadavers had a luminal anatomical variation. Forty-four percent and 42% of sinuses dissected had occurrence of a septations or blind pouches, respectively. Thirty percent of septations and 25% of pouches were classified as large. Incidence of anatomical variations was not statistically significant between cadaver gender or sinus laterality. Luminal variations are present in the transverse and sigmoid sinuses at rates higher than expected. This study is the first to report the presence of blind pouches in the luminal wall of transverse and sigmoid sinuses. These variations can have clinical importance to the endovascular surgeon and may also contribute to the pathophysiological etiology of venous sinus diseases. Anat Rec, 299:1037-1042, 2016. © 2016 Wiley Periodicals, Inc.

A novel reference coordinate system to locate the inferomedial point of the transverse-sigmoid sinus junction.

BACKGROUND: A coordinate system was previously developed to identify landmarks on the skull surface to help locate the transverse-sigmoid sinus junction in order to reduce surgical morbidity in retrosigmoid craniotomy; however, in practice we found that this system has important flaws. OBJECTIVE: To develop and evaluate a novel reference coordinate system to precisely locate the inferomedial point of the transverse-sigmoid sinus junction (IMTS) and evaluate the effect of gender and skull side (left or right). METHODS: Forty-two adult skulls (84 sides) were obtained for analyses. The X-axis was defined by point A (where the upper edge of the zygomatic arch joins with the frontal process of the zygomatic bone) and point B (where the upper edge of the zygomatic arch blends posterosuperiorly into the supramastoid crest). The Y-axis was defined by the line perpendicular to the X-axis and extending across the tip of the mastoid. The x and y coordinates of IMTS (IMTS-x and IMTS-y) were measured in this coordinate system. RESULTS: There were 20 male skulls and 22 female skulls. The mean IMTS-x measurements were significantly higher on the right side compared with the left side in both males and females. For the left skull side, the mean IMTS-y measurements were significantly lower in females compared with males. CONCLUSION: This novel reference coordinate system may be a reliable and practical method for identifying the IMTS during retrosigmoid craniotomy. There are significant differences in location of the axes with regard to gender and skull side.

Determining the morphometry and variations of the confluens sinuum and related structures via a silicone painting technique on autopsy patients.

In this study, we aimed to investigate the morphometric and morphologic structures of the confluens sinuum (CS) and related structures with a silicone painting technique. We studied 30 cadavers. Twelve of them were washed with alcohol and filled with a silicone painting technique via the vena jugularis interna, internal carotid artery, and vertebral artery. The other 18 were autopsied postmortem. The CS and related structures were dissected under microscope. Their anatomy was investigated, and variations were noted. The diameters of the sinus sagittalis superior (SSS), CS, occipital sinus (OS), sinus rectus (SR), and bilateral transverse sinus (TS), and the angle between SSS and SR were measured. The mean diameters were 11.7 mm for SSS, 22.3 mm for CS, 5.25 mm for OS, 7.5 mm for SR, and 9.7 (right) and 9.1 mm (left) for TS. The angle between the SR and SSS was 58°. There was no difference in the bilateral venous structures that drained to the SSS and TS. There was an extra drainage to the CS from the left side in 4 cases. The right TS was located superiorly in 7 cases compared with the left TS, and this process was correlated with the type of CS. A septum in the SSS was detected in 2 cases. In addition, we encountered an OS in 80% of the cases. We conclude that the septum inside the CS affects the dominancy of the TS, the angle between the SSS and SR, and the other venous variations.

External landmarks for identifying the drainage site of the vein of Labbé: application to neurosurgical procedures.

INTRODUCTION: The vein of Labbé is an important structure of the lateral cortical surface. However, to date, studies aimed at providing external landmarks for aiding in its identification have been scant. Therefore, the present study focussed on establishing reliable bony landmarks for localizing this deeper lying venous structure. MATERIALS AND METHODS: Fifteen adult cadavers (30 sides) underwent dissection of the lateral cortical brain surface with special attention given to the drainage site of the vein of Labbé into the transverse sinus. Measurements of the distance from this site to surrounding external bony landmarks were then made. RESULTS: We found that this drainage site into the transverse sinus was 0.8-1.5 cm (mean 1.1 cm, SD 0.567) superior to the superior border of the zygomatic arch and 2 - 5 cm (mean 2.9 cm, SD 0.713) posterior to the opening of the external auditory meatus. Statistically, there was no significance between left and right sides or between sexes. CONCLUSIONS: We found that the junction between the vein of Labbé and transverse sinus may be variable. Nonetheless, additional landmarks found in this study for identifying the junction may aid in its earlier identification during surgery, potentially decreasing operative morbidity.

Intracranial MR venography using low-field magnet: normal anatomy and variations in Nepalese population.

INTRODUCTION: Magnetic resonance (MR) venography is considered a reliable imaging modality for the evaluation of intracranial venous system. The purpose of this study was to evaluate the normal venous anatomy and its variations in Nepalese population using low field MR technique. METHODS: One hundred patients with normal MR imaging of brain underwent MR venographic study. MR venograms were performed in 0.35 T MR scanner using a contiguous 2D time-of-flight MR angiographic technique. RESULTS: The flow gaps in the transverse sinus were seen in 47% of population, of which 91% occurred in the non-dominant side. Right transverse sinus was dominant in 73% population. Flow gap was observed in bilateral transverse sinus in one case, while it was seen in the dominant right transverse sinus in 6.3% population. Inferior sagittal sinus was observed in 11% cases. Internal cerebral vein was seen in 60 cases. Occipital sinus was observed in 4% of the cases. The basal vein of Rosenthal was observed in 34% of the cases, whereas vein of Labbe seen in 8% cases. Unilateralflow gap in the sigmoid sinus was seen in 5 cases. CONCLUSIONS: MR angiography done at low field MR unit is a reliable tool in cerebral venous sinus assessment, particularly major dural sinuses. The flow gaps in transverse sinus are frequently encountered anatomic variation. Visualization of small veins like inferior sagittal sinus, basal vein of Rosenthal, vein of Labbe, internal cerebral vein was inferior in our study compared to other studies done in high field MR unit.

Correlative anatomy for the electrophysiologist, Part I: the pericardial space, oblique sinus, transverse sinus.

There is an increasing need for invasive electrophysiologists to appreciate the exact anatomy of the epicardial space and the coronary veins. The location of the epicardial fat, the complementary relationship with the main cardiac veins, and the location of sensitive structures (arteries, phrenic nerve, esophagus) have become required knowledge for electrophysiologists, and accessing the epicardial space with this thorough knowledge of the pericardial sinuses and recesses is essential to allow radiographic correlation during catheter manipulation. In this review, we briefly describe the anatomy of the pericardial space and then discuss the specific correlation for the invasive electrophysiologist, highlighting epicardial access, catheter navigation, and avoidance of collateral injury with specific attention to the important recesses of the pericardial space, their regional anatomy, and radiographic correlation when navigating catheters to these locations. We also discuss the anatomy of the main cardiac veins in the context of catheter mapping and ablation of the epicardial substrate through the venous system and without subxiphoid pericardial access. In Part I of this two-part series, we discuss the regional anatomy of the pericardial space, oblique sinus, and transverse sinus.

Mapping hV4 and ventral occipital cortex: the venous eclipse.

While the fourth human visual field map (hV4) has been studied for two decades, there remain uncertainties about its spatial organization. In analyzing fMRI measurements designed to resolve these issues, we discovered a significant problem that afflicts measurements from ventral occipital cortex, and particularly measurements near hV4. In most hemispheres the fMRI hV4 data are contaminated by artifacts from the transverse sinus (TS). We created a model of the TS artifact and showed that the model predicts the locations of anomalous fMRI responses to simple large-field on-off stimuli. In many subjects, and particularly the left hemisphere, the TS artifact masks fMRI responses specifically in the region of cortex that distinguishes the two main hV4 models. By selecting subjects with a TS displaced from the lateral edge of hV4, we were able to see around the vein. In these subjects, the visual field coverage extends to the lower meridian, or nearly so, consistent with a model in which hV4 is located on the ventral surface and responds to signals throughout the full contralateral hemifield.

Surface anatomy of the transverse sinus for the midline infratentorial supracerebellar approach.

AIM: Knowing the location of the transverse sinus in the midline supracerebellar infratentorial approach is important to prevent its inadvertent injury. The external landmarks of the occipital bone have been studied in this anatomic study in order to reveal their relationship with the transverse sinus. MATERIAL AND METHODS: Fifty-two dried skulls were used to study the relationship of the transverse sinus with various surface bone structures. The key bone surface structures identified in each specimen were the superior nuchal line, the inferior nuchal line, the inion, internal occipital protuberance, and the transverse sulcus. RESULTS: The distance from the inion to the inferior nuchal line in specimens ranged from 12.7 mm to 37.7 mm. The distance from the inferior nuchal line to the midline foramen magnum in the specimens ranged from 19 mm to 34.75 mm. The width of the proximal transverse sulcus ranged from 2.6 mm to 10.16 mm with an average of 6.43 mm on the right side and 3.4 mm to 10.6 mm with an average of 6.15 mm on the left. CONCLUSION: The first and most superior burr hole for midline supracerebellar infratentorial approach can be safely placed approximately 1 cm below the inferior nuchal line. A burr hole in this localization will avoid the transverse sinus.

Anatomic position of the asterion in Kenyans for posterolateral surgical approaches to cranial cavity.

The asterion, defined as the junction between lambdoid, parietomastoid, and occipitomastoid sutures, has been used as a landmark in posterolateral approaches to the posterior fossa. Its reliability however has been put into question due to its population-specific variability in position, using external palpable landmarks and its relation to the transverse-sigmoid sinus complex. This study aimed at determining the anatomic position of the asterion in a Kenyan population. Measurements from the asterion to the root of zygoma and the tip of mastoid process, respectively were taken on both left and right sides of 90 (51 male, 39 female) human skulls. The relation of the asterion to the transverse-sigmoid sinus junction was also determined. The distances on the right and left sides from the asterion to the root of the zygoma were 58.85 +/- 2.50 mm and 58.44 +/- 2.12 mm, respectively. The asterion was 47.89 +/- 3.72 mm above the tip of mastoid process on the right side and 47.62 +/- 2.87 mm on the left side. This point was significantly higher in males (48.36 +/- 2.72 mm) than in females (46.62 +/- 3.37 mm) with a P-value of 0.041. Regarding its position from the transverse-sigmoid sinus junction, it was at the junction in 72 cases, below it in 17 cases (average 3.68 mm) and only one case had the asterion above this junction (2.57 mm). The asterion therefore can reliably be ascertained using the parameters from the root of the zygoma and the tip of the mastoid process. The safest approach would be posteroinferior to the asterion so as to avoid lacerating the transverse-sigmoid sinus complex.

The anatomical basis of venographic filling defects of the transverse sinus.

Obstruction of the intracranial dural venous sinuses would result in an increase in intracranial dural venous pressure. This intracranial hypertension is not only the result of poor cerebral venous drainage but also life threatening. The aim of this study was to identify the structures, which may show signs of potential venographic filling defect qualities, including trabeculae/septa (also described as "fibrous bands") and arachnoid granulations, which ultimately can lead to increased intracranial dural sinus venous pressure. A total of 102 cadavers and living patients were used for the study. Fifty-three percent of the subjects presented with structures in their transverse sinuses that could be potential venous filling defects. Thirty percent of the subjects presented with arachnoid granulations in the right transverse sinus, which were found to be significantly dominant (Chi-square; p < 0.05). The study also revealed the presence of 1 to 5 septa in 29.4% of the subjects. The septa were found to be more dominant in the central (30%) and lateral (22%) thirds of the right transverse sinuses, while the central third of the left transverse sinus proved to be the least dominant occurring site (8%). In general, the right transverse sinus is highly more significantly dominant in septal occurrence (Chi-square; p < 0.01) than the left transverse sinus. We conclude from the statistical evidence that the right transverse sinus demonstrates significantly more potential venographic filling defects than the left sinus and submit that this information may assist in management options for patients diagnosed with idiopathic intracranial hypertension as well as direct future research.

Localization of the internal auditory canal by identifying the intersection of the posterior border of the trigeminal ganglion and the superior petrosal sinus in cadavers.

The identification of the internal auditory canal (IAC) has relied on visualization of the arcuate eminence (AE). However, it is not uncommon that the topographic markers on the middle cranial base are featureless and difficult to identify, including the AE. "Point T", the intersection of the posterior border of the trigeminal ganglion (TG) and the superior petrosal sinus (SPS) has been presented as a marker to localize the IAC. Thirty-four sides from 17 dry skulls and five formalin-fixed latex-injected cadaver heads were studied. In the dry skull, the imaginary line of the IAC was defined by connecting the uppermost point of the rim of the external auditory canal and the uppermost point of the porus acousticus on the petrosal ridge. Point T was defined as the posterior margin of the trigeminal impression on the petrosal ridge. For cadaver heads, a standard middle fossa approach was performed, and the line of the IAC was defined by joining the tip of Bill's Bar and the midpoint of the dura on the porus acousticus. Point T was expressed as the intersection of the posterior border of the TG and the SPS. The distance between point T and the medial end of the IAC was termed "segment TI", and the angle spanning from segment TI to the IAC was "angle theta (theta)". In dry skulls, segment TI (mean+/-standard deviation [SD]) measured 9.74+/-0.71mm and angle theta was 135.56+/-3.21 degrees ; in cadaver heads, segment TI measured 10.25+/-0.58mm and angle theta measured 133.43+/-2.00 degrees . An alternative for localization of the IAC is proposed when the AE is difficult to identify in the middle cranial fossa. As a mnemonic, the IAC can be located by identifying point T first, and then tracing 1cm posteriorly along the SPS and turning laterally 90 degrees plus half of 90 degrees (135 degrees total).

Anatomo-radiological correlation of the superior aspect of the temporal lobe (planum supratemporale)

The superior aspect of the temporal lobe or planum supratemporale (PS) forms the inferior limit of the sylvian fissure. It is related to the frontal, parietal and insular lobes, and with the sylvian vessels (arteries and veins). Recognition of the portions of PS in imaging studies, such as MRI or cranial CT, is important for neuroradiologists, neurologists and neurosurgeons. We used 10 formalin-fixed cerebral hemispheres. We injected red latex into the arterial system in one. We made horizontal, coronal and sagittal cuts in 7 hemispheres, and performed white matter dissection in two. We compared the anatomical specimens with MRI, cranial CT and cerebral angiographies. The PS can be divided into three portions from front to back: the planum polare (PP), Heschl’s gyrus (HG) and the planum temporale (PT). PP and PT are flat, and HG is elevated. The obliquity of HG is oriented in such a way that it delineates the location of the ventricular atrium. The three parts of PS can be readily identified in MRI, but a certain degree of brain atrophy facilitates its identification in CT. In cerebral angiography, the different segments of the middle cerebral artery serve as a guide for recognizing the anatomical structures of the temporal lobe and insular region. Anatomical knowledge is of paramount importance to recognize the different parts of the PS in radiological studies. This anatomicimage-based knowledge can be applied in surgical planning (AU)

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