The Posterior Auricularis Muscle as Superficial Landmark for the Sigmoid Sinus and Transverse-Sigmoid Sinus Junction: An Anatomical Study.

OBJECTIVE: Neuronavigation systems coupled with previously reported external anatomical landmarks assist neurosurgeons during intracranial procedures. We aimed to verify whether the posterior auricularis muscle (PAM) could be used as an external landmark for identifying the sigmoid sinus (SS) and the transverse-sigmoid sinus junction (TSSJ) during posterior cranial fossa surgery. METHODS: The PAM was dissected in 10 adult cadaveric heads and after drilling the underlying bone, the relationships with the underlying SS and TSSJ were noted. The width and length of the PAM, and the distance between the muscle and reference points (asterion, mastoid tip, and midline), were measured. RESULTS: The PAM was identified in 18 sides (9 left, 9 right). The first 20 mm of the muscle length (mean 28.28 mm) consistently overlay the mastoid process anteriorly and the proximal half of the SS slightly posteriorly on all sides. The superior border was a mean of 2.22 mm inferior to the TSSJ and, especially when the muscle length exceeded 20 mm, this border extended closer to the transverse sinus; it was usually found at a mean of 3.11 mm (range 0.0-13.80 mm) inferior to the distal third of the transverse sinus. CONCLUSIONS: Superficial landmarks give surgeons improved surgical access, avoiding overexposure of deep neurovascular structures and reducing brain retraction. On the basis of our cadaveric study, the PAM is a reliable and accurate direct landmark for identifying the SS and TSSJ. The PAM could potentially be used for guiding the retrosigmoid approach.

Renal vein valves: a prevalence, microanatomical and histological study.

PURPOSE: In the modern era of robotic renal procedures and diagnostics, an even more detailed anatomical understanding than hitherto is necessary. Valves of the renal veins (RVV) have been underemphasized and have been disputed by some authors, and few textbooks describe them. The current anatomical study was performed to address such shortcomings in the literature. METHODS: One hundred renal veins were studied in fifty adult formalin-fixed cadavers. Renal veins were removed from the abdomen after sectioning them flush with their entrance to the renal hilum. The inferior vena cava was then incised longitudinally and opened, and RVV were examined grossly and histologically. A classification scheme was developed and applied to our findings. RESULTS: Nineteen RVVs were observed in the fifty cadavers (38%). Four (8%) valves were found on right sides and fifteen (30%) on left sides. The valves were seen as cord/band-like, folds, and single and double leaflets. Histologically, they were all extensions of the tunica intima. CONCLUSION: On the basis of our study, RVV are not uncommon. They were more common on left sides, and on both sides, they were found within approximately one centimeter of the junction of the inferior vena cava and renal vein. Although the function of such valves cannot be inferred from this anatomical study, the structures of the Single leaflet valve (TS2) and Double leaflet valve (TS3) valves suggest they could prevent venous reflux from the IVC into the kidney.

Angulation of the dural venous sinuses of the posterior cranial fossa: Anatomical study with clinical and surgical applications.

Cerebral vein and dural venous sinus thromboses (CVST) account for 0.5%-1% of all strokes. Some structural factors associated with a potentially higher risk for developing CVST have been described. However, angulation of the dural venous sinuses (DVS) has yet to be studied as a structural factor. The current study was performed because this variable could be related to alterations in venous flow, thus predisposing to a greater risk of CVST development. Additionally, such information could help shed light on venous sinus stenosis (VSS) at or near the transverse-sigmoid junction. The angulations formed in the different segments of the grooves of the transverse (TS), sigmoid (SS), and superior sagittal sinuses (SSS) were measured in 52 skulls (104 sides). The overall angulation of the TS groove was measured using two reference points. Other variables were examined, such as the communication pattern at the sinuses' confluence and the sinus grooves' lengths and widths. The patterns of communication between sides were compared statistically. The most typical communication pattern at the sinuses' confluence was a right-dominant TS groove (82.98%). The mean angulations of the entire left TS groove at two different points (A and B) were 46° and 43°. Those of the right TS groove were 44° and 45°. The median angulations of the left and right SSS-transverse sinus junction grooves were 127° and 124°. The mean angulations of the left and right TS-SSJsv grooves were 111° (range 82°-152°) and 103° (range 79°-130°). Differentiating normal and abnormal angulations of the DVSs of the posterior cranial fossa can help to explain why some patients are more susceptible to pathologies affecting the DVSs, such as CVST and VSS. Future application of these findings to patients with such pathologies is now necessary to extrapolate our results.

Evolution of the term "epicondyle of the femur": Revisiting the anatomical and surgical literature.

The femoral epicondyle is an anatomical bony landmark essential for surgeons and anatomists, but there are discrepancies between the two fields when using this term. In current orthopedic surgery, it commonly denotes the small bony prominence of the femoral condyle. Given the derivation, "epicondyle" should be a region projecting laterally from the articular surface rather than a point. These discrepancies in usage are found not only between the fields but also in the literature. This article reviews the narrative definition of "epicondyle of the femur" in surgery and the evolution of the term in anatomy. The outcomes of the review suggest a relationship between the differing perceptions of the epicondyle and the evolution of the term. In reports of studies related to the epicondyle, it is strongly recommended that the definition of the word is clearly stated, with an understanding of its evolution.

L5 spondylolysis: Anatomical study comparing healed and unhealed lesions.

The anatomy and pathogenesis of spondylolysis has been widely studied; however, the microanatomy of spondylolysis of the lumbar vertebra has not been well described. Therefore, we aim to better elucidate this anatomy. Twenty dry bone specimens of healed and unhealed spondylolysis of the L5 vertebra were collected from human skeletal remains. Twelve L5 vertebrae were examples of unhealed spondylolysis and eight specimens exhibited a healed (i.e., bony fusion of the lesion) spondylolysis lesion. The specimens underwent macro and microanatomical analysis followed by CT and microCT imaging. Finally, selected healed and unhealed lesions were submitted for histological analysis using Mason Trichrome staining. The pars interarticularis of two L5 vertebrae without signs of healed/unhealed spondylolysis were evaluated histologically as controls. Of the 12 unhealed L5 pars defects, three were unilateral on left side. Of the eight healed pars defects, all were unilateral and seven of these were on left sides. One unilateral pars defect also had spina bifida occulta. Both on imaging and histological analysis, healed pars defects were only so superficially and not at deeper levels. Histologically, unhealed edges were made up of dense cortical bone while healed edges were made up primarily of trabecular bone. Based on our anatomical findings, the so-called healed spondylolysis lesions, although externally fused, are not thoroughly fused internally. Moreover, the anterior and posterior edges of the unhealed spondylosysis lesions are irregular and show signs of long-term disarticulation. Taken together, these data suggest that such 'healed' lesions might not be as stable as the normal L5 pars interarticularis.

Decibel Decisions: The Concept of Intracranial Aneurysm Surgery With a Decibel Meter on Two Surgical Cases.

The present cases were used to investigate the reliability of the intraoperative decibel meter as an objective method of clipping efficiency in cerebral aneurysm surgery and to assess the impact of this method on the surgical procedure itself. Different methodologies have been developed and applied to directly or indirectly evaluate the placement of a clip, for example, intraoperative digital subtraction angiography (DSA), intraoperative micro-Doppler ultrasonography, and, more recently, indocyanine green (ICG). We included two patients with a previously non-treated unruptured brain aneurysm. In both patients, intraoperative micro-Doppler was used in combination with a decibel meter app. Here, we present the cases of two patients. In patient one, the pre-clipping average sound level/equivalent continuous sound pressure level (Avg/Leq) was 96.7 dB, while the post-clipping Avg/Leq was 94.4 dB, indicating a reduction in sound level after clipping. Similarly, the pre-clipping time-weighted average noise level (TWA) was 1.2%, while the post-clipping TWA was 0.5%, indicating a decrease in exposure dose after clipping. In patient two, the average sound level for the post-clipping measurement (94.2 dB) was higher than the pre-clipping measurement (93.5 dB), but the difference was not statistically significant. These cases indicate the potential for using sound measurements as a reliable indicator of adequate aneurysm occlusion during clipping procedures. Further research is needed to confirm these findings.

Dural sinus septum as an underlying cause of intrinsic venous sinus stenosis: Anatomical, clinical, and stent placement considerations.

Recently, an interesting study regarding "Dural sinus septum: an underlying cause of cerebral venous sinus stenting failure and complications." was published, to our knowledge, being the launching point of the clinical/interventional applications of this intraluminal variation. Herein, we wish to highlight paramount anatomical, clinical, and stent placement considerations related to DSS located in the dural venous sinus at the posterior cranial fossa and the interventional complications caused by the presence of this variation during stenting procedures.

Trabeculae in the basilar venous plexus: anatomical and histological study with application to intravascular procedures.

Few studies have examined the basilar venous plexus (BVP) and to our knowledge, no previous study has described its histology. The present anatomical study was performed to better elucidate these structures. In ten cadavers, the BVP was dissected. The anatomical and histological evaluation of the intraluminal trabeculae within this sinus were evaluated. Once all gross measurements were made, the clivus and overlying BVP were harvested and submitted for histological analysis. A BVP was identified in all specimens and in each of these, intraluminal trabeculae were identified. The mean number of trabeculae per plexus was five. These were most concentrated in the upper half of the clivus and were more often centrally located. These septations traveled in a posterior to anterior direction and usually, from inferiorly to superiorly however some were noted to travel horizontally. In a few specimens the trabeculae had wider bases, especially on the posterior attachment to the meningeal layer of dura mater. More commonly, the trabeculae ended in a denticulate form at their two terminal ends. The trabeculae were on average were 0.85 mm in length. The mean width of the trabeculae was 0.35 mm. These septations were consistent with the cords of Willis as are found in the lumen of some of the other intradural venous sinuses. An understanding of the internal anatomy of the BVP can aid in our understanding of venous pathology. Furthermore, this knowledge will benefit patients undergoing interventional treatments that involve the BVP.

Quadricuspid Pulmonary Valve With Fenestration: Cadaveric Findings.

Quadricuspid pulmonary valves (QPV) are rare entities. Such valves can be associated with other cardiac anatomical anomalies. In this report, we present a case of a quadricuspid valve with an additional variant and discuss the morphometrics of this anatomical variation. During the routine dissection of an adult male body, two anatomical variations were found within the pulmonary trunk. This individual had a QPV. In addition, one of the leaflets of this valve contained fenestrations. No additional cardiac anomalies were identified. Clinicians who review imaging of the heart or treat patients with cardiac conditions should be well-informed about QPV.

Review of the caroticotympanic nerves: Anatomy, function and pathology.

The caroticotympanic nerves provide postganglionic sympathetic fibres to the tympanic plexus. However, there are scant reports in the literature detailing with these nerves in great depth. As the caroticotympanic plexus lies near the often-operated tympanic nerve, it is important for the surgeon to understand the anatomy, pathology and surgical implications of it. Here, we present a review of the available literature regarding the caroticotympanic nerves.

Revisiting the transorbital approach for emergency external ventricular drainage: an anatomical study of relevant parameters and their effect on the effectiveness of using Tubbs' point.

The transorbital approach (TOA) can provide immediate access to the lateral ventricles by piercing the roof of the orbit (ROO) with a spinal needle and without the need of a drill. Reliable external landmarks for the TOA ventriculostomy have been described, however, the necessary spinal needle gauge and other relevant parameters such as the thickness of the ROO have not been evaluated. Nineteen formalin-fixed adult cadaveric heads underwent the TOA. Spinal needles of different gauges were consecutively used in each specimen beginning with the smallest gauge until the ROO was successfully pierced. The thickness of the ROO at the puncture site and around its margins was measured. Other parameters were also measured. The TOA was successfully performed in 14 cases (73.68%), where the most suitable needle gauge was 13 (47.37%), followed by a 10-gauge needle (36.84%). The mean thickness of the ROO at the puncture site, and the mean length of the needle to the puncture site were 1.7 mm (range 0.2-3.4 mm) and 15.5 mm (range 9.2-23.4 mm), respectively. A ROO thickness of greater than 2.0 mm required a 10-gauge needle in seven cases, and in five cases, a 10-gauge needle was not sufficient for piercing the ROO. The presence of hyperostosis frontalis interna (HFI) (21.05%) was related to the failure of this procedure (80%; p < 0.00). Using a 13/10-gauge spinal needle at Tubbs' point for TOA ventriculostomy allowed for external ventricular access in most adult specimens. The presence of HFI can hinder this procedure. These findings are important when TOA ventriculostomy is considered.

Histology and immunohistochemistry of the human carotid sinus nerve.

The carotid sinus nerve (CSN) is well known as mediating baroreflexes. However, studies of its detailed histological analysis are scant in the literature. Therefore, the current anatomical study sought to better elucidate the microanatomy of the CSN. Ten fresh frozen adult cadavers underwent dissection of the CSN. Then, it was harvested and submitted for histological and immunohistochemical staining. Specimens were all shown to be nerve fibers on histology and immunohistochemistry. We identified tyrosine hydroxylase positive fibers in all CSN specimens. These fibers were always found to be within the CSN and not on its surface i.e., epineurium. Based on our findings, the majority of fibers contained in the CSN are tyrosine positive in nature. Further studies are necessary to understand the true function of this autonomic nerve fibers.

Fenestrated popliteal vein pierced by a branch of the tibial nerve.

Knowledge of anatomical variations is important so as to avoid potential iatrogenic injury or misdiagnosis on imaging. Here we report an unusual finding and relationship between the tibial nerve and popliteal vein. During the routine dissection of an adult cadaver, it was noted that a branch of the tibial nerve in the popliteal fossa pierced the most distal part of the popliteal vein. This unusual finding is described and relevant reports in the literature discussed. Our hopes are that such a report might help surgeons avoid injury to such a fenestrated popliteal vein and the tibial nerve branch traveling through it therefore decreasing patient morbidity.

Innervation of pineal gland by the nervus conarii: a review of this almost forgotten structure.

The nervus conarii provides sympathetic nerve innervation to the pineal gland, which is thought to be the primary type of stimulus to this gland. This underreported nerve has been mostly studied in animals. One function of the nervus conarii may be to activate pinealocytes to produce melatonin. Others have also found substance P and calcitonin gene-related peptide from the nervus conarii ending in the pineal gland. The following paper reviews the extant medical literature on the nervus conarii including its anatomy and potential function.

Twenty Intracranial Skull Base Variations in the Same Specimen.

Anatomists and clinicians often encounter single bony anatomical variations in dry skulls and on imaging. However, a constellation of 20 such variants some that, to our knowledge, have not been previously described is noteworthy. Here, we describe an adult skull with multiple bony variations, and these are detailed and discussed. These included clival canals, an interclinoid bar with resultant foramen at the uppermost aspect of the clivus, middle clinoid process, posterior petroclinoid ligament, pterygoalar plate, septated hypoglossal canal, foramen through the anterior clinoid process, septated foramen ovale, shortened superior orbital fissure, and crista muscularis. Knowledge of individual differences in the structure of the skull may be of use to both anatomists and clinicians in the treatment of intracranial procedures as well as cranial imaging studies. Taken together, such a unique specimen is of archival value.

The Occipitalis Muscle as an Adjunct Superficial Landmark for the Transverse Sinus and Transverse-Sigmoid Junction: An Anatomical Study With Application to Posterior Cranial Fossa Surgery.

INTRODUCTION: Although neuronavigation systems are widely used for identifying deep intracranial structures, additional superficial anatomical landmarks can be useful when this technology is not available or is not working properly. Herein, we investigate the potential of the occipitalis muscle (OM), rarely mentioned in neurosurgical literature, as a superficial landmark for the transverse sinus (TS) and transverse-sigmoid sinus junction (TSJ). METHODS: Eighteen adult cadaveric heads underwent dissection. The borders of the OM were identified and measured. The muscle was then removed and the bone underlying the muscle was drilled. The relationships between the OM and the underlying dural venous sinuses were then investigated by using a surgical microscope. RESULTS: The OM is a quadrangular-shaped muscle, that invariably crosses the lambdoid suture, showing relationships with the TS inferiorly and the TSJ laterally. The medial border was located a mean of 2.7 cm from the midline and its lower edge was a mean of 1.6 cm above the TS. The inferior border was found between the lambdoid suture and the superior nuchal line in all the specimens. The medial half of the inferior margin was placed on average 1.1 cm superiorly to the TS while the lateral margin ran just above or over the TS. The lateral border was located a mean of 1.1 cm medially to the asterion and approximated the mastoid notch, being within 1-2 cm from it. The TSJ was between 2.1 and 3.4 cm lateral to OM lateral border. CONCLUSION: A combination of superficial anatomical landmarks can be useful for surgical planning. We found that the OM represents a valuable aide for neurosurgeons and is a reliable landmark for the deeper-lying TS and TSJ.

Nerve to subclavius for neurotization procedures: an anatomical feasibility study.

Injuries to the inferior trunk of the brachial plexus and its components can be debilitating. As such injuries are prioritized by surgeons during repair, an additional nerve transfer is considered herein. In the supine position, 13 adult cadavers (26 sides) underwent dissection of the nerve to subclavius and the proximal brachial plexus in the supraclavicular region. Once the nerve was located and isolated from origin to termination, measurements of its length and diameter were made. Next, the C8 and T1 roots and inferior trunk were identified. The distal end of the nerve to subclavius was transected and swung to these roots and the inferior trunk. Once the nerves to subclavius were transposed and in a tension-free manner, the length of excess nerve following being brought to each of these nerves was measured. A nerve to subclavius was identified on all sides. The nerve originated from the superior trunk and traveled anterior to the middle and inferior trunks on all sides. The mean diameter of the nerve to subclavius was 0.8 mm, and the mean length was 57 mm. After cutting the nerve to subclavius at its entrance into the subclavius muscle, the distal nerve could be transferred tension free to the inferior trunk of the brachial plexus and T1 ventral ramus on all sides. The distal nerve to subclavius reached the T1 ventral ramus with an average of 18 mm of additional length and to the C8 ventral ramus with an average of 19 mm. The nerve also could be transferred to the inferior trunk of the brachial plexus with an average of 20 mm of additional length. The nerve to subclavius was found to have approximately 3000 axons. To our knowledge, use of the nerve to subclavius has previously not been used for nerve transfer procedures. Based on our cadaveric study, this often-overlooked nerve can be easily transposed to other regional nerves such as the inferior trunk of the brachial plexus.

The superior vesical artery: A review of conflicting definitions and how these could affect invasive procedures.

Since the superior umbilical artery is the only functioning branch of the patent umbilical artery, some anatomical and surgical books/atlases fail to clarify that it is a branch of the umbilical artery and not a direct branch of the anterior division of the internal iliac artery and so specifically state that it is a direct branch of the internal iliac artery. This discrepancy in nomenclature can obviously affect invasive procedures and communication between physicians. Therefore, the present review is intended to highlight this issue. The term "superior vesical artery" was searched using standard search engines, for example, PubMed and Google Scholar. Several standard and specialized anatomy textbooks were also examined to ascertain how the superior vesical artery was described. Thirty-two articles were identified that used the terms "superior vesical artery" or "superior vesical arteries." After applying exclusion criteria, in 28 papers, the definition of the superior vesical artery was undetermined in eight, described as a direct branch of the internal iliac artery in 13, described as a branch of the umbilical artery in six, and defined as being equivalent to the umbilical artery in one. Of the sampled textbooks, some defined the superior vesicle artery as a branch of the umbilical artery, some as a direct branch of the internal iliac artery and some as both. Taken all together, most define the superior vesical artery as a branch of the umbilical artery. As the superior vesical artery is described as a branch of the umbilical artery in the internationally accepted terminology (Terminologia Anatomica), we recommend that this definition be used by anatomists and physicians alike so that communication is clear.

Epiglottic Epidermoid Cyst: Cadaveric Case Report and Clinical-Surgical Applications.

An epidermoid cyst is lined with stratified squamous epithelium with a lumen filled with fluid, in most cases. Such cysts can occur anywhere in the body; however, they are rarely found on the epiglottis (0.54%). Herein, we describe to our knowledge, the first cadaveric case of a regular, circular, and soft mass extending out from the tip of the epiglottis with consistent histological characteristics of an epidermoid cyst. Epiglottic cysts are rare and mostly asymptomatic. However, through this case report, we aimed to highlight the clinical-surgical applications presented mainly when they grow large enough, to cause issues with ventilation or obstruct endotracheal tubes, thus interfering with airway management. Additionally, such cysts can affect swallowing or speaking.

What is the C2 pedicle, pars interarticularis, and isthmus? Anatomical study and review of the literature regarding these confusing terms with proposal of new nomenclature.

INTRODUCTION: The atypical anatomy of the C2 vertebra has led to terminological discrepancies within reports and studies in the literature regarding the location of its pedicle, pars interarticularis, and isthmus. These discrepancies not only limit the power of morphometric analyses, but they also confuse technical reports regarding operations involving C2, and thus confuse our ability to properly communicate this anatomy. Herein, we examine the variations in nomenclature regarding the pedicle, pars interarticularis, and isthmus of C2, and via an anatomical study, propose new terminology. METHODS: The articular surface and underlying superior and inferior articular processes and adjacent transverse processes were removed from 15 C2 vertebrae (30 sides). Specifically, the areas regarded as the pedicle, pars interarticularis, and isthmus were evaluated. Morphometrics were performed. RESULTS: Our results indicate that, anatomically, C2 has no "isthmus" and that a pars interarticularis for C2, when present, is very short. Deconstruction of the attached parts allowed for visualization of a bony arch extending from the anterior most aspect of the lamina to the body of C2. The arch is composed almost entirely of trabecular bone and without its attached parts, e.g., transverse process, really has no cortical bone laterally. CONCLUSIONS: We propose a more accurate terminology, the pedicle, for pars/pedicle screw placement of C2. Such a term more accurately describes this unique structure of the C2 vertebra and would alleviate terminological confusion in the future literature on this topic.