Mastoid emissary foramina: an anatomical morphological study with discussion on their evolutionary and clinical implications

Mastoid Emissary Foramina in Dry Skulls: Its Morphometry, Topography, and Associated Clinical Implications

Mastoid emissary foramen transmitting mastoid emissary vein connects the posterior auricular vein with the sigmoid sinus. This foramen and so the mastoid emissary vein varies in prevalence, number, size and location, knowledge of which is essential for carrying out uneventful surgeries, especially retrosigmoid, mastoidectomy, and skull base surgeries. There is a paucity of literature on this foramen in the Indian context, so the study was done. The purpose of the study is to elaborate on the prevalence, number, size, and location of mastoid foramen in dry adult skulls. The study was conducted in the Department of Anatomy using 90 dry skulls of unknown age and sex, and prevalence, number, size, and location in these skulls were noted. The mastoid foramen was detected in 27.8% of skulls, with an incidence of 31.1% and 12.2% on right and left sides of skulls, respectively. The number of foramina ranged between 1 and 4. The mean diameter of this foramen was 0.9 mm, and the most frequent location was mastoid process. The detailed morphology and morphometry of mastoid foramen are of utmost use to neurosurgeons, ENT surgeons, radiologists, and vascular surgeons as it transmits mastoid emissary vein and meningeal branch of the occipital artery, which may be injured during various surgical procedures involving mastoid region and skull base causing catastrophic hemorrhage. In addition to this, mastoid emissary vein may be the source of thrombus, causing thrombus of sigmoid sinus creating helm of neurological complications.

Anatomical study of the mastoid foramina and mastoid emissary veins: classification and application to localizing the sigmoid sinus

The mastoid foramen (MF) is located on the mastoid process of the temporal bone, adjacent to the occipitomastoid suture or the parietomastoid suture, and contains the mastoid emissary vein (MEV). In retrosigmoid craniotomy, the MEV has been used to localize the position of the sigmoid sinus and, thus, the placement of the initial burr hole. Therefore, this study aimed to examine the exact location and variants of the MF and MEV to determine if their use in localizing the sigmoid sinus is reasonable. The sample in this study comprised 22 adult dried skulls (44 sides). MF were identified and classified into five types based on location, prevalence, whether they communicated with the sigmoid sinus and exact entrance into the groove of the sigmoid sinus. The diameters and relative locations of the MF in the skull were measured and recorded. Finally, the skulls were drilled to investigate the course of the MEV. Additionally, ten latex-injected sides from human cadavers were also dissected to follow the MEV, especially in cases with more than one vein. We found that type I MFs (single foramen) were the most prevalent (50%). These MFs were mainly located on the occipitomastoid suture; only one case on the right side was adjacent to the parietomastoid suture. Type II (paired foramina) was the second most prevalent (22.73%), followed by type III (13.64%), type 0 (9.09%), and type IV (4.55%). The diameter of the external opening in a connecting MF (2.43 ± 0.79) was twice that of a non-connecting MF (1.14 ± 0.56). Interestingly, on one side, two MFs on the external surface shared a single internal opening; the MEV bifurcated. MFs followed three different courses: ascending, almost horizontal, and descending. Regardless of how many external openings there were for the MF, these all ended at a single opening in the groove for the sigmoid sinus. For cadaveric specimens with multiple MEVs, all terminated in the sigmoid sinus as a single vein, with the more medial veins terminating more medially into the sinus. Based on our study, the MF/MEV can guide the surgeon and help localize the deeper-lying sigmoid sinus. Knowledge of this anatomical relationship could be an adjunct to neuronavigational technologies.

Prevalence, morphology, morphometry and associated clinical implications of mastoid emissary veins: narrative review

The mastoid emissary vein connects the posterior auricular vein to the sigmoid sinus and varies in size, number, location, and course, resulting in clinical complications. This study was conducted in response to the vast clinical implications associated with this vein. The aim of this review is to highlight and describe the prevalence, varied morphology, and morphometry of the mastoid emissary vein, how these varied parameters cause clinical complications, and how these can be rectified and avoided. A literature survey was conducted using various databases and different terms related to mastoid emissary vein were used to search the literature. Pitfalls related to surgery in the vicinity of this vein and their remedies were elucidated. The literature search revealed that the prevalence, morphology, and morphometry of mastoid emissary veins vary immensely and are responsible for morbidity and mortality. Pre-operative identification of mastoid veins is thus essential and so multidetector computed tomography of the temporal bone should be scheduled before planning surgery.

Abdelkarim A, Syed AZ, Orhan K. Morphometric and morphological evaluation of mastoid emissary canal using cone-beam computed tomography

OBJECTIVES

This study aimed to determine mastoid emissary canal's (MEC) and mastoid foramen (MF) prevalence and morphometric characteristics on cone-beam computed tomography (CBCT) images to underline its clinical significance and discuss its surgical consequences.

METHODS

In the retrospective analysis, two oral and maxillofacial radiologists analyzed the CBCT images of 135 patients (270 sides). The biggest MF and MEC were measured in the images evaluated in MultiPlanar Reconstruction (MPR) views. The MF and MEC mean diameters were calculated. The mastoid foramina number was recorded. The prevalence of MF was studied according to gender and side of the patient.

RESULTS

The overall prevalence of MEC and MF was 119 (88.1%). The prevalence of MEC and MF is 55.5% in females and 44.5% in males. MEC and MF were identified as bilateral in 80 patients (67.20%) and unilateral in 39 patients (32.80%). The mean diameter of MF was 2.4 ± 0.9 mm. The mean height of MF was 2.3 ± 0.9. The mean diameter of the MEC was 2.1 ± 0.8, and the mean height of the MEC was 2.1 ± 0.8. There is a statistical difference between the genders (p = 0.043) in foramen diameter. Males had a significantly larger mean diameter of MF in comparison to females.

CONCLUSION

MEC and MF must be evaluated thoroughly if the surgery is contemplated. Radiologists and surgeons should be aware of mastoid emissary canal morphology, variations, clinical relevance, and surgical consequences while operating in the suboccipital and mastoid areas to avoid unexpected and catastrophic complications. CBCT may be a reliable imaging diagnostic technique.

The morphometric analysis of mastoid foramen and mastoid emissary canal on cone-beam computed tomography (CBCT)

PURPOSE

The purpose of this retrospective study was to assess the prevalence and morphometric features of the mastoid foramen (MF) and mastoid emissary canal (MEC) using cone-beam computed tomography (CBCT), as well as their relationship with age, sex, and side.

METHODS

CBCT scans of 500 patients aged 8-87 years were examined retrospectively. The presence and number of MF, mean diameter of the MEC and MF, MF location, and the distance between MF and asterion were all examined. The collected data were subjected to appropriate statistical analysis. P values < 0.05 were accepted as statistically significant at a 95% confidence interval.

RESULTS

The study included 472 patients. MF was present in 82% and absent bilaterally in 18% of the 472 patients. The prevalence of MF was 67.8% on the right side and 65.7% on the left. The mean diameter of the MF was 3.39 ± 1.48 mm and the number of the MF ranged from zero to four. The mean diameter of the MEC was 2.05 ± 1.06 mm and the distance between MF and asterion was 22,46 ± 5,18 mm. 52.4% of the MF was observed on the occipito-mastoid suture.

CONCLUSION

To prevent surgical complications, particularly those that concern the temporal and mastoid areas, radiologists should report the results of the preoperative examination of the morphometry of the MF and MEC. CBCT imaging is a reliable diagnostic method that can be used to evaluate the MEC and MF before surgical procedures.

Clinical applications of the mastoid emissary vein

PURPOSE

During retrosigmoid craniotomy, the mastoid emissary vein (MEV) can be a source of considerable bleeding during the operation, especially when the larger diameter MEV or sigmoid sinus is torn. In this study, we evaluated the relevant structure of the MEV for their anatomy and applied the data in surgery to summarize their clinical significance.

METHODS

The posterior craniocervical regions of 15 silicon-injected Chinese human cadaver specimens were dissected to expose the MEV and adjacent structures. Fifty-one patients who were scheduled to undergo retrosigmoid craniotomy were selected. All patients underwent preoperative routine CT of the head. The relevant data were collected on cadaveric anatomy and CT. Eventually, all patients underwent retrosigmoid craniotomy and the MEV was observed during the operation.

RESULTS

In cadaver specimens, the prevalence of the MEV was 90.0%. It originated from the middle and lower parts of the posterior wall of the sigmoid sinus and extended in the posterior direction in the mastoid process, usually having 1-2 external openings (86.7%) and only 1 internal opening. The intraosseous courses of the MEV were classified as straight and curved. The straight type accounted for 57.9%, and the curved type for 42.1%. The mean diameter of the MEV was 1.84 ± 0.85 mm, and the straight length of the MEV inside the mastoid process was 11.93 ± 3.58 mm. In 16.7% and 6.7% of all cadaver specimens, the MEV diameter was greater than 2.5 and 4 mm, respectively. In 51 patients (bilateral), routine head CT scan showed the MEV in 49.0% of the patients, and the MEV diameter was greater than 2.5 and 4 mm, respectively, in 17.6% (18/102) and 3.9% (4/102) of the cases. During surgery (unilateral) in the 51 patients, 48 had the MEV and 3 had no MEV. None of the patients had sigmoid sinus tears or massive bleeding.

CONCLUSION

In the process of retrosigmoid craniotomy, detailed anatomical knowledge of the MEV, well-planned CT scan, and meticulous microsurgical techniques are key for successful operation, which can reduce the occurrence of complications.

The parietal foramen anatomy: studies using dry skulls, cadaver and in vivo MRI

OBJECTIVE

The aim of this study was to describe the anatomical features encountered in the parietal foramen in a series of 178 human bones and 123 head MRI examinations. A cadaveric specimen was also dissected to demonstrate the trajectory of a superficial scalp vein through the parietal foramen as far as the dura mater. A literature review was performed regarding prevalence of parietal foramen in different populations.

METHODS

Totally, 178 paired adult bones were used to investigate the presence, shape and number of the parietal foramina. In addition, 123 brain MRI examinations were also studied.

RESULTS

The parietal foramina were encountered in 75/89 (84.3%) skulls [32/38 (84.2%) in women vs. 43/51 (84.3%) in men, p > 0.05]. The parietal foramen was present bilaterally in 44.73% of females and 54.9% of males. Regarding unilaterality of the parietal foramen, a right or left laterality was observed in female 21% right versus 18% left; and 16% versus 14% (left) in males (p > 0.05). The accessory parietal foramen was present in the right parietal in 2.6% and in 7.9% on the left side of the females, while 5.9% and 3.9% of the males on the right or left sides, respectively. The parietal foramina located in the proximity of the sagittal suture (male 7.1 ± 2.5 mm vs. female, 7.4 ± 2.7 mm). There was a positive correlation between the right and left parietal foramina regarding the distance from the median line. The distance from a foramen to the contralateral one was 16 ± 4 mm in men and 18 ± 5 mm in women, respectively (p > 0.05).

CONCLUSION

No major differences were encountered between sexes regarding the anatomical features of parietal foramen.

Comprehensive review of the mastoid foramen

Anatomical variations of the mastoid foramen have been observed to vary in a number of qualities including size, number, and location. These variants have the potential to become problematic during surgical approaches to the posterior cranial fossa and mastoid part of the temporal bone, and should thus be appreciated by the surgeon. Herein, we discuss the mastoid foramen in detail including issues with such foramina that should be known to the neurosurgeon.

Persistent fetal superficial middle cerebral vein: an anatomical study

The superficial middle cerebral vein (SMCV) drains the venous blood from most of the superolateral surface of the brain and drains typically into the cavernous sinus as mentioned in standard textbooks. But the drainage of the SMCV is variable as indicated by various radiological studies. Although variations in the drainage of the SMCV exist, there is a shortage in the literature providing cadaveric evidence for the same. The present study was designed to identify the variations in the drainage pattern of the SMCV in fetal cadavers. During the dissection of formalin-fixed full-term fetuses, deviation in the drainage of the SMCV was observed in five out of 30 cases. In three out of 30 specimens (10%), SMCV was observed draining into superior petrosal sinus; and in two specimens (6.6%) into the transverse sinus. In the remaining specimens, the SMCV drained directly into the cavernous sinus. Knowledge of the variations noted in the present study is essential, not only for diagnosing several diseases involving the cavernous sinus or paracavernous sinuses but also in surgeries of paracavernous sinus lesions and endovascular treatment of arteriovenous fistulas. The SMCV and superior petrosal sinus can be a venous refluxing route in patients with arteriovenous fistulas.

Emissary veins prevalence and evaluation of the relationship between dural venous sinus anatomic variations with posterior fossa emissary veins: MR study

PURPOSE

The aim of this study was to find the prevalence of emissary veins and to compare the visibility of these emissary veins with the anatomic variations of the dural venous sinuses detected in magnetic resonance venography (MRV).

MATERIALS AND METHODS

All MR images of two hundred twenty patients were evaluated retrospectively. Posterior cranial fossa emissary veins diameter measurements were performed in the axial plane. The anatomic variations of the venous sinuses in MRVs of all patients were recorded. Accordingly, the presence of the emissary veins was compared with the dural venous sinus anatomic variations. p < 0.05 was considered statistically significant. An inter-observer reliability analysis was performed.

RESULTS

The prevalence of emissary veins in MRI was found in the right mastoid emissary vein (MEV) 82.7% and left MEV 81.4%. Occipital emissary vein (OEV) was present in 63 patients (28.6%) for the first radiologist (R1), and it was present in 61 patients (27.7%) for the second radiologist (R2) (K = 0.978). A statistically significant correlation was detected between the diameter of the left MEV and gender (p < 0.05) for both radiologists. There was a statistically significant difference between the left MEV and OEV and transverse sinus anatomic variations.

CONCLUSION

MR imaging is a noninvasive and irradiating imaging method for detecting posterior fossa major emissary veins, and we recommend using MR imaging for preoperative evaluation of posterior fossa major emissary veins and related dural venous sinuses.

Mastoid foramen, mastoid emissary vein and clinical implications in neurosurgery

BACKGROUND

Mastoid emissary vein is especially important from the neurosurgical point of view, because it is located in variable number in the area of the occipitomastoid suture and it can become a source of significant bleeding in surgical approaches through the mastoid process, especially in retrosigmoid craniotomy, which is used for approaches to pathologies localized in the cerebellopontine angle. Ideal imaging method for diagnosis of these neglected structures when planning a surgical approach is high-resolution computed tomography. The aim of this work was to provide detailed information about this issue.

METHODS

We studied a group of 295 skulls obtained from collections of five anatomy departments and the National Museum. Both quantitative and qualitative parameters of the mastoid foramen were evaluated depending on side of appearance and gender. Individual distances of the mastoid foramen from clearly defined surface landmarks (asterion, apex of mastoid process, foramen magnum) and other anatomical structures closely related to this issue (width of groove for sigmoid sinus, diameters of internal and external openings of mastoid foramen) were statistically processed.

RESULTS

The most frequently represented type of the mastoid foramen is type II by Louis (41.2%). The differences between right and left sides were not statistically significant. In men there was a higher number of openings on the right side and in qualitative parameters the type III and IV predominated, whereas in women the types I and II were more frequent. In men, greater distances from the mastoid foramen were observed when evaluating qualitative parameters for defined surface landmarks. Mean size of the external opening diameter was 1.3 mm; however, several openings measured up to 7 mm.

CONCLUSIONS

Despite excellent knowledge of anatomy, however, good pre-operative examination using imaging methods and mastering of microsurgical techniques create the base for successful treatment of pathological structures in these anatomically complex areas.

Incidental occurrence of an unusually large mastoid foramen on cone-beam computed tomography and review of the literature

The incidental finding of an enlarged mastoid foramen on the right posterior mastoid region of temporal bone is reported, together with a discussion of its clinical significance. A 67-year-old female underwent the pre-implant assessment of a maxillary left edentulous region. A cone-beam computed tomographic (CBCT) image was acquired and referred for consultation. Axial CBCT slices revealed a unilateral, well-defined, noncorticated, low-attenuation, transosseous defect posterior to the mastoid air cells in the right temporal bone. The borders of the osseous defect were smooth and continuous. No other radiographic signs suggestive of erosion or sclerosis were noted in the vicinity. The density within the defect was homogenous and consistent with a foramen and/or soft tissue. The patient's history and physical examination revealed no significant medical issues, and she was referred to a neuroradiologist for a second opinion. The diagnosis of an enlarged mastoid foramen was made and the patient was reassured.

Morphology and topography of the parietal emissary foramina in South Indians: an anatomical study

The objectives of the present study were to study the prevalence of the parietal emissary vein in adult South Indian population and to study the distance of foramen from the sagittal suture. There were 58 adult human skulls in the present study which were available at the anatomy department of our institution. The study included 116 parietal bones which have been observed macroscopically for the number, prevalence and topography of the emissary foramen. The emissary foramen was present in 83 parietal bones (71.5%) of the present study. It was present at the junction between the middle 1/3 and posterior 1/3 region of the parietal bone. The foramen was observed solitary in 73 parietal bones (62.9%), double in 8 bones (6.9%), and triple in 2 parietal bones (1.7%). The foramen was not observed in 33 parietal bones (28.4%). The bilateral absence of parietal emissary foramen was seen in 7 skulls (12.1%). It was absent unilaterally in 19 skulls (32.7%). The accessory foramina were seen in only 8 skulls (13.8%). The mean distance of the foramen from the sagittal suture was 6.7±2.9 mm and 6.8±2.8 mm on the right and left sides respectively. The prevalence of parietal emissary vein in the present study was 71.5%. The present study has observed important data about the morphology and morphometry of the parietal emissary vein in South Indian population. The identification of parietal emissary veins and accessory veins is important in the operation room to prevent the blood loss.

Morphological study of styloid process of the temporal bone and its clinical implications

The objective of this study was to study the morphometry of the styloid process of temporal bone and prevalence of elongated styloid process. The morphology of elongated styloid process along with its embryological and clinical importance are discussed. The present study included 110 human dry skulls which were procured from the bone collections of the department of anatomy. The styloid process was observed macroscopically on both sides of all the skulls, the elongations if any were noted. All the styloids were measured for their length, thickness at different levels and interstyloid distance at various levels. Out of 110 specimens, only 5 skulls (4.5%) exhibited the elongated styloid process. Among them, 3 skulls (2.7%) had unilateral elongation and 2 skulls (1.8%) had bilateral elongation of the styloid process. The mean length of the styloid process was 17.8±9.3 mm and 18.2±5.6 mm for the right and left sides, respectively. The prevalence of elongated styloid process in the present study was 4.5%. The clinical anatomy of this congenital variant is important to the neurosurgeon and radiologist, while interpreting the computed tomogram and magnetic resonance image scans. The morphological knowledge of elongated styloid process is clinically important since the course of the vertebral artery may be distorted in such situations.