Anatomical study of pterygoid canal (PC) and palatovaginal canal (PVC) in endoscopic trans-sphenoidal approach

Purpose

The primary purpose of our work was to make anatomical measurements of pterygoid canal (PC) and palatovaginal canal (PVC). The secondary goal was to locate the two structures based on the landmarks in the trans-sphenoidal surgery and draw a safe corridor of fenestration in the bottom of sphenoid sinus during surgical procedure to sphenopalatine region.

Materials and methods

Computed tomographic angiography (CTA) images of PC, PVC and sphenoid sinus in 200 adults were reviewed. Multiplanar reconstruction of the CT images was performed, and the anatomical features of the PC and PVC were studied in the coronal, sagittal, and axial planes. The length, diameter and direction of PC and PVC were measured in the plane through or perpendicular to them. The anterior and posterior opening of PC and PVC were identified by the surgical landmarks such as the middle lowest point of sellar floor, the sagittal midline and the bottom of the sphenoid sinus.

Result

Both PC and PVC can be found and identified easily on CTA image, the shape and size of the PC and PVC were in agreement with those retrieved from previous literatures, the position of them can be located by the anatomical landmarks in sphenoid sinus.

Conclusion

Knowing the anatomical features of PC and PVC and their location based on the anatomical landmarks are helpful to the endoscopic trans-sphenoidal surgery. These data in our study will provide surgeons a better understanding of PC and PVC and their relationship to sphenoid sinus. Notably, it will not help the surgeons to avoid injuring neurovascular structures as well as provided supportive information for the choice of the appropriate endoscopic equipment.

     

神经内镜经蝶窦入路的解剖标志研究及其临床应用

目的:探讨神经内镜下经鼻蝶窦入路的解剖标志,并将其应用于神经内镜经蝶垂体瘤手术.方法:8具成人尸头标本,模拟内镜下经鼻蝶窦入路,鼻腔、蝶窦和鞍底分阶段观察并测量解剖标志;指导临床实施内镜下经鼻蝶窦垂体瘤手术10例.结果:内镜下经蝶入路可清晰显露各阶段解剖标志,蝶窦开口下缘距后鼻孔上缘为(15.4±1.8)mm;蝶窦开口中心点至鞍底中心点相距(13.4±2.1)mm;双侧视神经颈内动脉隐窝(OCR)连线中点至鞍底中心点距离(11.0±2.8)mm;鞍底均位于中线部位,以鞍底为中心,可看到鞍底前外方的视神经隆突,侧下方的颈内动脉隆突,前上方可见鞍结节,后方可见斜坡凹陷.10例内镜经蝶垂体瘤手术患者,肿瘤全切除7例(70%),次全切除3例(30%);术后患者临床症状都得到明显改善.结论:熟悉蝶鞍区结构的内镜下解剖关系有助于手术中准确定位,避免损伤重要的神经、血管结构,以提高手术成功率,减少并发症的发生.     

Allele frequencies of hemojuvelin gene (HJV) I222N and G320V missense mutations in white and African American subjects from the general Alabama population

Background

The TM4SF10 gene encodes a putative four-transmembrane domains protein of unknown function termed Brain Cell Membrane Protein 1 (BCMP1), and is abundantly expressed in the brain. This gene is located on the short arm of human chromosome X at p21.1. The hypothesis that mutations in the TM4SF10 gene are associated with impaired brain function was investigated by sequencing the gene in individuals with hereditary X-linked mental retardation (XLMR).

Methods

The coding region (543 bp) of TM4SF10, including intronic junctions, and the long 3' untranslated region (3 233 bp), that has been conserved during evolution, were sequenced in 16 male XLMR patients from 14 unrelated families with definite, or suggestive, linkage to the TM4SF10 gene locus, and in 5 normal males.

Results

Five sequence changes were identified but none was found to be associated with the disease. Two of these changes correspond to previously known SNPs, while three other were novel SNPs in the TM4SF10 gene.

Conclusion

We have investigated the majority of the known MRX families linked to the TM4SF10 gene region. In the absence of mutations detected, our study indicates that alterations of TM4SF10 are not a frequent cause of XLMR.     

Anatomical landmarks for locating the sphenoid ostium during endoscopic endonasal approach: a cadaveric study

Purpose

The sphenoid ostium (SO) provides a natural portal for entering the sphenoid sinus and beyond up to the skull base. It is not always easy to locate the ostium during the endoscopic approach. The present study was designed to establish readily identifiable anatomical landmarks for locating the sphenoid ostium.

Methods

Cadaveric dissection was performed in 30 hemisections of head and neck and various measurements were taken from fixed anatomical landmarks in the nasal cavity to the sphenoid ostium. The size, shape and position of sphenoid ostium were determined in relation to the anterior wall of the sphenoid sinus and the superior turbinate.

Results

The mean distance from the supero-lateral angle of the posterior choana to the SO was found to be 21.21 ± 6.02 mm. The mean distance of the SO from the midline was 4.85 ± 2.89 mm. In all the specimens, the SO was situated within 1 cm of the midline. The mean distance between the inferior end of the SO and the postero-inferior edge of the superior turbinate was 8.03 ± 3.52 mm. The SO was present on an average distance of 55.1 ± 3.54 mm from the limen nasi. In 93.3 % of the specimens, the SO was situated between 5 and 6 cm of the inferior end of the limen nasi. The angle between the anterior nasal spine and the SO was found to be remarkably constant. In 93.3 % of the specimens, it was from 25° to 30°.

Conclusions

The sphenoid ostium could be localized medial to the superior turbinate between 1.5 and 3 cm above the supero-lateral angle of the posterior choana, within 1 cm of the midline and within 1 cm of the postero-inferior edge of the superior turbinate.     

Evaluation of the surgical anatomy of sphenoid ostium with 3D computed tomography

Purpose

To evaluate the anatomy of the sphenoid ostium (SO), which has so far only been investigated with the aid of two-dimensional computed tomography (CT) or using a cadaver, from a new point of view through the use of 3D CT for the first time.

Methods

We have evaluated 50 patients who had CT angiography done for different reasons. The sphenoid sinus types and the SO were evaluated three dimensionally. The average diameters of the sphenoid ostia, and their distances to the midline, as well as to each other and the choana have been measured. In addition, the SO were categorized according to their shapes.

Results

The average age of the patients was 48.5. No SO was found in seven cases (14 %). The average distance of the SO to the midline was 2.78 mm on the right side and 2.77 on the left. Four different shapes of SO were determined; round, oval, irregular and linear. The average distance of the right and left SO to the choana was 15.22 ± 0.95 and 14.87 ± 1.11 mm, respectively. No statistically significant difference was found between the male and female sexes with regard to the calculated diameters and shapes of the SO (p > 0.05).

Conclusion

The anatomy of the sphenoid sinus and the SO varies widely from individual to individual. We have demonstrated in our study that these anatomic variations could be evaluated pre-operatively. Using this imaging technique, surgeons can make a pre-operative 3D evaluation of the sphenoid ostium, encountered in the surgery and thus achieve better orientation.     

The anatomic relationship around the horizontal segment of petrous internal carotid artery: a study based on reconstructed computed tomography angiography

Purpose

The anatomic relationship around the horizontal segment of petrous internal carotid artery (ICA) is complicated. Relative researches on human patients using radiographic technique are scarce. It is essential to get adequate anatomic knowledge about this region for performing some bypass procedures.

Methods

Using the independent software Mimics, we prospectively studied the 0.45-mm-thick computed tomography angiography (CTA) images of 29 patients (58 sides). All patients’ middle cranial fossa and related critical anatomic structures were reconstructed in 3D. Some measurements were established on the multiplanar reconstructed images, including the distance from foramen ovale and foramen spinosum to the petrous ICA; the distance from the lumen of cochlea to the edge of trigeminal impression and petrous ICA; and the length of the horizontal segment of petrous ICA.

Results

The horizontal segment of petrous ICA was surrounded by the trigeminal impression, the cochlea and the auditory tube spatially. On the multiplanar reconstructed CTA images, the average distances from foramen ovale and foramen spinosum to the petrous ICA were 4.1?mm and 5.8?mm, respectively; the average distance from the lumen of cochlea to the edge of trigeminal impression and petrous ICA were 8.2?mm and 2.0?mm, respectively; and the mean length of the horizontal segment of petrous ICA was 15.8?mm.

Conclusions

Our results indicate adequate and reliable anatomic information can be obtained using reconstructed CTA on an individualized basis.     

Geometric classification of the carotid siphon: association between geometry and stenoses

Purpose

The development of intracranial internal carotid artery (ICA) stenoses may be associated with the morphology of the siphon. The aim is to quantitatively characterize the geometry of ICA, and develop a classifier of the ICA shape in relation to the location and incidence of stenoses.

Methods

The ICA geometry from 74 subjects was analyzed by means of image-based computational techniques. The siphon was split into two bends, and was described in terms of curvature radius, radius of vessel, angle of bending, and length. Differences of geometry between ICA classes were assessed in control group, consisted of 30 subjects without stenoses. In stenosed group, the association between the ICA classes and the incidence of stenoses were investigated and validated by hemodynamic simulation.

Results

The curvature radius and angle of the posterior bend were significantly different between ICA classes, as well as the angle between the two bends. An innovative classifier was developed with the three geometric parameters. The ICA classification was found associated with the incidence of stenoses at the siphon.

Conclusions

Geometric factors relative to the ICA were correlated with the location and incidence of stenoses at the siphon. The present work has potential implications in the quest for hemodynamic factors contributing to the initiation and progression of intracranial ICA stenoses.     

相关解剖定位标志在经单鼻孔-蝶窦垂体腺瘤显微外科切除术中的应用

目的：探讨相关解剖定位标志在经单鼻孔-蝶窦入路垂体腺瘤显微外科手术中的应用。方法：62例垂体腺瘤经单鼻孔-蝶窦入路显微手术，术中根据蝶嵴、蝶窦开口、蝶窦中隔、鞍底隆凸等解剖标志进行定位。结果：蝶嵴是术中确认手术入路中线的可靠标志，蝶窦开口是蝶窦前壁的重要标志，鞍底隆凸可作为蝶窦腔内鞍底定位标志。62例术中依靠相关解剖标志，均准确定位蝶窦及鞍底，未出现偏差。肿瘤全切除52例，次全切除5例，大部分切除4例。1例部分切除，无死亡病例。结论：熟悉相关解剖标志，有助于该术式的准确定位，从而安全实施手术。     

Calvarial diploic venous channels: an anatomic study using high-resolution magnetic resonance imaging

Background

The calvarial diploic venous channels (CDVCs) are well-known intraosseous structures, but their distribution and anatomofunctional implications are not fully understood.

Objective

To investigate the architecture of CDVCs using high-resolution magnetic resonance (MR) imaging.

Method

This prospective study enrolled 43 male and 37 female outpatients who underwent a 3.0-T MR imaging equipped by a 32-channel head coil. T1-weighted imaging covering the whole cranial vault was performed after gadolinium injection. In addition, one-piece orbitozygomatic craniotomy was performed in three cadaveric heads to observe the interruption of the CDVCs.

Results

The CDVCs showed irregular contours and peculiar branching patterns with four common major pathways: the pteriofrontparietal (PFP), frontoorbital (FO), occipitoparietal (OP), and occipitocervical (OC) routes. The proximal PFP coursed as a single trunk and divided into several branches at the level of the frontal eminence. The orbital part of the FO continued to the subcutaneous vein via the supraorbital rim. The PFP and the pterional part of the FO fused proximally with the sphenoparietal sinus and descended as the middle meningeal vein. The OP coursed in the superoinferior direction and connected the junction part of the transverse-sigmoid sinus to the parietal superior sagittal sinus. The OC occurred as a single trunk in the median occipital bone, drained extracranially, and joined the suboccipital venous channels.

Conclusions

The CDVCs seem to be a relatively consistent network functioning not only as conduits connecting the intracranial dural sinuses but also as pathways to the extracranial venous systems. High-resolution MR imaging is useful for investigating the CDVCs.     

Position of the greater palatine foramen: an anatomical study through cone beam computed tomography images

Purpose

The block anesthesia of the greater palatine foramen (GPF) is largely used in minor oral surgeries, periodontics and general dentistry. Furthermore, the area of the GPF serves as a donor of soft tissue graft. So, the aim of this study was to evaluate the position and characteristics of the GPF in Brazilian patients using cone beam computed tomography (CBCT) providing anatomical information for the greater palatine nerve block anesthesia and indicate site to collect palatal donor tissue.

Methods

Fifty CBCT exams of Brazilian patients with a mean age of 35.8 years (27 male/23 female) were evaluated. All patients had erupted first, second and third upper molars. A total of 100 GPF were evaluated bilaterally. The GPFs were assessed regarding position, diameter and distances to the midline maxillary suture (MMS) and to alveolar ridge (AR). Guidelines were drawn in the CBCT axial image depicting all molar interproximal surfaces, bilaterally. The guidelines were located between first, second and third molar and in the center of the second and third, performing five guidelines in each side. These guidelines and the molars were landmarks to assess the GPF anatomic position.

Results

From the 100 GPF analyzed, 92 were located in the third molar region (24 male/22 female). The 92 GPF were distributed as 47 in the left side and 45 in the right side. The average GPF diameter and the distance to both the AR and the MMS were 3.1 mm; 7.9 and 15.3 mm, respectively.

Conclusions

Within the limits of this study, we concluded that the in Brazilian patients studied, the GPF location was more closely related to third molar. Therefore, whenever the third molar is erupted, it could be used as landmark for successful GPN block anesthesia. Moreover, harvesting palatal mucosa graft around the third molar should be done cautiously to prevent damage to the GPF vascular-nerve complex.     

Variations in the branching pattern of posterior division of mandibular nerve: a case report

Purpose

Abnormal communications among the branches of mandibular nerve especially the posterior division are significant due to various procedures undertaken in this region. These variations are worth reporting as they pose serious implications in several interventions in this region, and may even lead to false diagnosis.

Methods

During routine dissection, the mandibular nerve and its branches were dissected in the infratemporal fossa. The branches from the posterior division of the mandibular nerve namely the inferior alveolar and auriculotemporal nerves were carefully dissected, and their abnormal branching pattern was noted.

Results

There was a communicating branch between left inferior alveolar and auriculotemporal nerve. There was also a variant recurrent branch from the left inferior alveolar nerve that supplied the lateral pterygoid muscle.

Conclusions

Such variant branches and communications between the branches of mandibular nerve as seen in this case have an embryological basis and are clinically important in this region especially for dental surgeries and anesthesia.     

The hazards of lack of co-registration of ictal brain SPECT with MRI: A case report of sinusitis mimicking a brainstem seizure focus

Background

Single photon emission computed tomography (SPECT) following injection of radiotracer during a seizure is known as ictal SPECT. Comparison of an ictal SPECT study to a baseline or interictal study can aid identification of a seizure focus.

Case presentation

A young woman with encephalitis and refractory seizures underwent brain SPECT during a period of frequent seizure-like episodes, and during a seizure-free period. A focal area of increased radiotracer uptake present only when she was experiencing frequent seizure-like episodes was originally localized to the brainstem, but with later computerized co-registration of SPECT to MRI, was found to lie outside the brain, in the region of the sphenoid sinus.

Conclusion

Low-resolution SPECT images present difficulties in interpretation, which can be overcome through co-registration to higher-resolution structural images.     

The circumventricular organs of the brain: conspicuity on clinical 3T MRI and a review of functional anatomy

Purpose

The circumventricular organs (CVOs) occupy seven midline locations around the ventricles. They contain specialized ependymal cells called tanycytes and have an incomplete blood–brain barrier (BBB). We hypothesized that appearances of the lesser known CVOs on contrast-enhanced MRI might lead to confusion in image interpretation whereby they might be mistaken for pathology-related abnormal contrast enhancement. We therefore assessed the normal appearances and prevalence of contrast enhancement of the CVOs on routine clinical brain MRI and reviewed the functional anatomy of the CVOs.

Methods

We retrospectively reviewed sagittal and coronal pre- and post-contrast T1-weighted brain 3T MR images in 100 adult patients with normal findings. We assessed the presence of the median eminence (ME), neurohypophysis (NH), pineal gland (PG), subforniceal organ (SFO), organum vasculosum of the lamina terminalis (OVLT), subcommissural organ (SCO), and the area postrema (AP).

Results

The frequency of contrast enhancement of the seven CVOs was as follows: ME in 100 %, NH in 96 %, PG in 84 %, SFO in 1 %, OVLT in 34 %, SCO in 0 %, and AP in 2 %.

Conclusions

The main CVOs (ME, NH, and PG) are well known and appreciated on brain imaging. However, there is a little awareness of the minor CVOs among neuroimagers. This is the first study of contrast enhancement prevalence of the SF, OV, SC, and AP on brain MRI. All the latter are small, faint, rarely visualized, and therefore not likely to cause misinterpretation with significant sources of pathology that cause breakdown of the BBB, such as tumor or inflammation.     

Location of the ankle center for total knee arthroplasty

Background

The purpose of this study was to investigate the ankle center position as determined from the malleoli for total knee arthroplasty (TKA).

Evaluation of location and dimensions of mandibular lingual foramina using cone-beam computed tomography

Objectives

The aim of this study was to assess the regional frequency and anatomical properties of mandibular lingual foramina (MLF) and their bony canals with cone-beam computed tomography (CBCT).

Materials and methods

A retrospective study was conducted by selecting images of the mandible from CBCT examination of 500 patients. MLF were located according to tooth areas and were grouped into midline, paramedian, and posterior foramina. In addition, the frequency of bony canals originating from lingual foramina was calculated, and the course and anastomoses were examined.

Results

In total, 491 areas with lingual foramina were observed. The highest regional frequency was recognized in the midline area (95.2 %), followed by left first premolar (15.1 %) area. The frequency of foramina in the midline was different from the paramedian and posterior (p < 0.01) regions. 95.6 % of lingual vascular canals originating from midline lingual foramina had a perpendicular course into the symphysis, whereas 60.3 % of canals from paramedian foramina and 83.6 % of canals from lateral lingual foramina presented with an anteriorly directed course.

Conclusions

CBCT examination easily demonstrates the presence of the lingual vascular canals. MLF are frequently present in a Turkish population; radiologists and oral surgeons should be aware of this anatomic feature and its possible implications.     

A morphometric anatomical and comparative study of the foramen magnum region in a Greek population

Background

The foramen magnum (FM), a complex area in craniocervical surgery, poses a challenge for neurosurgeons. The knowledge of the detailed anatomy of the FM, occipital condyles (OC) and variations of the region is crucial for the safety of vital structures. This study focuses on the FM and OC morphometry, highlights anatomical variability and investigates correlations between the parameters studied.

Materials and methods

One hundred and forty-three Greek adult dry skulls were examined using a digital sliding calliper (accuracy, 0.01 mm).

Results

Mean FM width and length were found 30.31 ± 2.79 and 35.53 ± 3.06 mm, respectively. The commonest FM shape was two semicircles (25.9 %), whereas the most unusual was irregular (0.7 %). The OC minimum width, maximum width and length were 5.71 ± 1.61, 13.09 ± 1.99 and 25.60 ± 2.91 mm on the right, and 6.25 ± 1.76, 13.01 ± 1.98 and 25.60 ± 2.70 mm on the left side. The commonest OC shape was S-like and the most unusual was ring, bilaterally. The mean anterior and posterior intercondylar distances were 19.30 ± 3.25 and 51.61 ± 5.01 mm, respectively. The OC protruded into the FM in 86.7 % of the skulls. Variations such as a third OC existed in 5.6 % and basilar processes in 2.8 %. Posterior condylar foramina were present in 75.5 %. The gender was correlated with FM width and length, OC length, bilaterally, anterior intercondylar distance (AID) and posterior intercondylar distance (PID). The OC protrusion and existence of posterior condylar foramina were correlated. Bilateral asymmetry for OC shape was statistically significant.

Conclusion

Our results provide useful information that will enable effective and reliable surgical intervention in the FM region with the maximum safety and widest possible exposure.     

D-chiro-inositol Negatively Regulates the Formation of Multinucleated Osteoclasts by Down-Regulating NFATc1

Purpose

Osteoclasts (OCs) are multinucleated giant cells that resorb bone matrix. Accelerated bone destruction by OCs might cause several metabolic bone-related diseases, such as osteoporosis and inflammatory bone loss. D-pinitol (3-O-methyl-D-chiro-inositol) is a prominent component of dietary legumes and is actively converted to D-chiro-inositol, which is a putative insulin-like mediator. In this study, we analyzed the effect of D-chiro-inositol on OC differentiation.

Methods

To analyze the role of D-chiro-inositol on OC differentiation, we examined OC differentiation by the three types of osteoclastogenesis cultures with tartrate-resistant acid phosphatase (TRAP) staining and solution assay. Then, we carried out cell fusion assay with purified TRAP⁺ mononuclear OC precursors. Finally, we analyzed the effect of D-chiro-inositol on OC maker expression in response to the regulation of nuclear factor of activated T cells c1 (NFATc1).

Results

We demonstrated that D-chiro-inositol acts as an inhibitor of receptor activator of NF-κB ligand-induced OC differentiation. The formation of multinucleated OCs by cell-cell fusion is reduced by treatment with D-chiro-inositol in a dose-dependent manner. In addition, we demonstrated that D-chiro-inositol inhibits the expression of several osteoclastogenic genes by down-regulating NFATc1.

Conclusions

We have shown that D-chiro-inositol is negatively involved in osteoclastogenesis through the inhibition of multinucleated OC formation by cell-cell fusion. The expression of NFATc1 was significantly down-regulated by D-chiro-inositol in OCs and consequently, the expression of OC marker genes was significantly reduced. Hence, these results show that D-chiro-inositol might be a good candidate to treat inflammatory bone-related diseases or secondary osteoporosis in diabetes mellitus.     

蝶窦的应用解剖学研究

目的　为经蝶手术安全切除鞍区肿瘤提供解剖学参数。方法　对 2 0例经 10 %福尔马林溶液固定成人尸头的蝶窦进行观察和测量。结果　 80 %蝶窦为全鞍型 ,其中 12 5 %为鞍枕型 ;仅 2例蝶窦中隔位置居中 ,占 10 % ;鞍底骨质厚度平均为 0 9mm ,其中≤ 1mm者占 5 5 %。颈内动脉在蝶窦内形成隆凸者占 4 5 %。结论　蝶窦中隔不能作为术中中线定位的惟一标准 ;鞍底向两侧扩大时要注意勿损伤颈内动脉海绵窦段     

Molecular identification of Lodoicea maldivica (coco de mer) seeds

Background

The edible endosperm of Lodoicea maldivica with the common name of coco de mer is used in Chinese medicine for treating cough. Native to Seychelles, Lodoicea maldivica seeds have commanded high prices for centuries due to its scarcity. This study aims to develop a molecular identification method for the authentication of Lodoicea maldivica seeds.

Methods

DNA was extracted from the sample. Two polymerase chain reaction (PCR) systems were developed to amplify a region of the chloroplast DNA and the nuclear phosphoribulokinase (PRK) region specific to Lodoicea maldivica respectively. DNA sequence of a sample was determined and compared with that of the Lodoicea maldivica reference material.

Results

The PRK gene of Lodoicea maldivica was successfully amplified and sequenced for identification.

Conclusion

A new molecular method for the identification of Lodoicea maldivica seeds in fresh, frozen or dried forms was developed.     

The anatomical and clinical details of the pterygoid canal: a three-dimensional reconstructive virtual anatomic evaluation based on CT

Purpose

To delineate the pterygoid canal (PC) configuration and its position in relation to surrounding important anatomical landmarks using three-dimensional reconstructive technology based on CT for the Chinese.

Methods

The computerized tomography arteriography (CTA) data of 137 patients were retrospectively evaluated using neuroimaging three-dimensional reconstructive software. The morphological parameters of the PC as well as the spatial relationship and distance between the PC relative to internal carotid artery (ICA) and the foramen rotundum were evaluated.

Results

83.9 % of the PC can be identified by our neuroimaging three-dimensional reconstructive software. The mean distance from the PC to the ICA was 2.6 ± 1.2 mm. The mean distance between medial aspects of bilateral ICA was 19.6 ± 2.7 mm. The distal vertical and horizontal distances between the PC and foramen rotundum were 5.2 ± 3.2 and 6.1 ± 2.8 mm, respectively. All the proximal end of the PC were inferior-lateral to the ICA. The PC mainly (92.9 %) ran posteriorly with a medial to lateral direction. The distance from the PC to ICA was positively correlated with the distance between bilateral ICA and the distal diameter of the PC. The vertical distance between the PC and foramen rotundum was positively correlated with the length of the PC and the horizontal distance between the PC and foramen rotundum.

Conclusions

Understanding the configuration and spatial relationship of the PC may be helpful to improve the accuracy and safety of operation during the expanded transnasal endoscopic approaches to skull base. The three-dimensional reconstructive virtual anatomic technology may be a useful tool to delineate the PC configuration and its position to surrounding important anatomical landmarks.