Background:The foramen magnum (FM) has garnered broad interest across the disciplines of anthropology, comparative anatomy, evolutionary biology, and clinical sciences. Most studies regarding the structure of the FM in humans have been intrapopulation morphometric studies rather than interpopulation morphologic studies. The few studies assessing the morphology of the foramen have utilized ambiguous and subjective descriptors to describe foraminal shape and are, consequently, difficult to reproduce. Therefore, detailed study of FM shape among craniofacially and geographically diverse populations through reproducible methods is warranted.Objectives:The aim of this study was to assess intersex and interpopulation differences in FM size and shape among diverse populations.Materials and Methods:The study analyzed 152 FMs of varied sex and race via traditional and geometric morphometric methods.Results and Conclusions:The study demonstrates that, within each distinct population, the size of the FM is significantly larger in males than in females; however, there are no significant differences in the shapes of the foramina between sexes. However, when comparing different populations to one another, there are significant differences with regard to both the size and shape of the FM. This study also presents a new model of FM ontogeny. Specifically, the growth occurring between the anterior and posterior foraminal boundaries before 5 years of age predicts the ultimate shape of the adult FM.

The debilitating pain of trigeminal neuralgia (TN) often necessitates neurosurgical intervention via percutaneous transovale cannulation. While most percutaneous treatments of TN are successful, severe adverse events resulting from failure to properly cannulate the foramen ovale (FO) have been reported. With regard to specific targeting of particular trigeminal divisions (i.e. V1, V2, V3, and combinations thereof), operative techniques have been described; however, these descriptions have not included specific angulation data. This anatomical study analyzed the angular relationship between the centroid and anteromedial- and posterolateral-most aspects of the FO and the boundaries of the trigeminal impression. The study is the first to detail the angular relationship between the FO boundaries and the boundaries of the trigeminal impression in dry human skulls relative to the coronal plane. The information may be used to prevent miscannulation and also target specific branches of the trigeminal nerve for optimal operative results.

Metopism, the persistence of the metopic suture in adulthood, is a clinically significant radiographic finding. In addition to masquerading as a fracture of the frontal bone, a persistent metopic suture may be associated with other clinically significant anatomical variations including frontal sinus abnormalities. Several geographically and craniofacially distinct populations have yet to be assessed for the prevalence of metopism. This study aimed to determine the prevalence of metopic sutures in adult crania of diverse populations among which scant research exists. A total of 505 adult crania were examined for the presence of a metopic suture. A total of 13 (2.57%) demonstrated metopism. Among subpopulations, metopism was present in 8.06% (5:62) of European crania, 15.38% (2:13) of East Asian crania, 2.20% (2:91) of Egyptian crania, and 2.86% (1:35) of Bengali crania. Metopism was also found in 1 Chilean, Roman, and Tchuktchi cranium, respectively. Metopism was not seen in crania from individuals of African (non-Egyptian) descent (0:62), Peruvians (0:144), Malayans (0:23), or Mexicans (0:23). Among sexes, metopism was present in 3.77% (8:212) of females and 1.79% (5:279) of males. The prevalence of metopism differs between populations and sexes. The results of this study provide anthropological, developmental, and clinical insight with regard to metopism.

Purpose-Submental anatomical variation is of clinical importance with regard to head and neck surgeries. One such anatomical variation is that of additional musculature joining the intermediate tendon of the digastric muscle to the midline of the mylohyoid musculature-a variation which this report refers to, accordingly, as an arrowhead variation. Though the arrowhead variation has been described in several case reports, it has not been subject to cross-sectional study. The purpose of this study is to determine the prevalence of the arrowhead variation. Methods-Prevalence of the arrowhead variation was assessed in 19 cadavers via gross dissection. Results-Two of the 19 cadavers (10.5%) were found to have arrowhead variations. The arrowhead variation was found in one male (1:11; 9.1%) and one female (1:8; 12.5%), respectively. Conclusions-This report demonstrates that the submental arrowhead variation of the anterior digastric and mylohyoid musculature has been reported in isolated case reports since the nineteenth century. This report is the first cross-sectional study of the arrowhead variant, identifying it in approximately one in ten individuals and in both sexes. Therefore, the presence of an arrowhead variation should be regularly considered with regard to diagnosis of submental masses. Likewise, the arrowhead variation should be considered in the preoperative planning of the myriad operations performed in the submental region.

Identification of the infraorbital foramen is important in infraorbital nerve block and the prevention of iatrogenic injury of the infraorbital nerve in maxillofacial surgeries. This study assessed the location of 887 infraorbital foramina from 518 adult crania of varied sex and population. The study assessed the midpoint of a line segment spanning from nasospinale to jugale (NS-J) relative to the infraorbital foramen. The mean distance of the NS-J midpoint from the infraorbital foramen was 2.1 ± 1.9 mm (mean ± SD) with a mode of 0 mm (266:887; 30%). The NS-J midpoint was located in the same plane or inferior to the infraorbital foramen in 98.4% of sides (873:887). There were no significant differences between sexes, populations, or sides with regard to the NS-J midpoint to infraorbital foramen distance. The NS-J midpoint can be used to locate the infraorbital foramen in both females and males of varied populations regardless of craniofacial diversity. The results of this study will aid in infraorbital nerve block procedures and maxillofacial surgery.

Identification of the infraorbital foramen (IOF) is important in infraorbital nerve block and the prevention of iatrogenic injury of the infraorbital nerve in maxillofacial surgeries. Though many methods have been proposed for identifying the location of the IOF, numerous inconsistencies exist among them. This study assessed the location of 1272 infraorbital foramina, from crania varied by age, sex, and geographic origin, relative to a midpoint of a line segment spanning from nasospinale to jugale (NS‐J). On average, the midpoint was located 1.92±1.85 mm (mean±SD) from the IOF. Most often, the midpoint was located either directly upon the IOF (Mode=0; 404:1272; 31.8%) or inferior to the IOF (403:1272; 31.7%). The NS‐J midpoint can be used to locate the infraorbital foramen in both females and males of varied geographic populations and ages regardless of craniofacial diversity. The results of this study may aid in the approach to infraorbital nerve block procedures and maxillofacial surgery.Support or Funding InformationWV Research Challenge Fund [HEPC.dsr.17.06] and [HEPC.dsr.14.13]This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.