Morphometry of organization of middle meningeal artery through the analysis of bony canal in human's skull: A clinico-anatomical and embryological insight.

BACKGROUND: Middle meningeal artery (MMA) is the largest branch of the maxillary artery supplying meninges of the cranial cavity. The complexity of MMA development gives many opportunities for anatomical variation. Besides, the variant MMA can be easily injured when dealing with fractures of the base of the skull, epidural hematomas, and bypass procedures. Although various aberrant origins of the MMA have been documented in the literature, there is a lack of detailed morphometric aspects of this important arterial segment. Thus, in this study, we investigated the anatomical organization of the MMA through the bony canal measurements from human skulls to improve surgical results.
MATERIALS AND METHODS: Seventy-five adult dry skulls were investigated. Angle of the main trunk, length of the main trunk, angle between the frontal and parietal branches, length of the frontal branch, length of the parietal branch, and length of the bony tunnel formed by the frontal branch were measured bilaterally.
RESULTS: In the present study, we found significant differences between the parameters such as length of frontal (P = 0.034) and parietal (P = 0.023) branches and length of bony tunnel (P = 0.045) of right and left sides, but there was no significant difference found in the rest of the parameters.
CONCLUSIONS: Morphometry of the bony canal of MMA shall be important for safely expose and preserve the artery during craniotomy with careful drilling and shall be useful for those who have interest in this anatomical site.

INTRODUCTION

The meningeal arteries can play an important role in the surgical revascularization; several studies have shown the significance of middle meningeal artery (MMA) in indirect bypass surgery such as encephaloduroarteriosynangiosis which supplies donor tissue, during craniotomy.[1] After the MMA enters the cranium through the foramen spinosum, the MMA runs anterolaterally and ascends to the pterion along the greater sphenoid wing and divides into frontal and parietal branches. Frontal branch of the MMA runs around the pterion (pterional segment) and ascends along the coronal suture[2] in a bony canal where it is susceptible for damage while removing the bone flap and in fractures.[3] For preserving the MMA during frontotemporal craniotomy, it should be exposed by drilling around the pterion.[45] Moreover, there is a lack of information about arterial organization and possible asymmetries between the right and left sides.[5] With the above in mind, the present study aimed to identify the course of the bony canal and to describe the morphological features of the bony canal structure to allow the MMA to be safely exposed and preserved during neurological surgery.

MATERIALS AND METHODS

Our study analyzed 75 adult skulls from the Laboratory of Human Anatomy at the Kannur Medical College, Kerala, India. Only skulls that had a bony tunnel and the groove formed from the MMA evident on both sides (right and left) were used. Pearson's correlation coefficients were calculated to determine the relationship between the results obtained by the two blinded researchers. Parameters studied included angle of the main trunk, length of the main trunk, angle between the frontal and parietal branches, and length of the frontal and parietal branches using orthodontic wire and goniometry[6] and digital caliper as shown in Figure 1.

Figure 1

Internal view of the skull showing the six measurements performed bilaterally: (1) angle of the main trunk, (2) length of the main trunk, (3) angle between the frontal and parietal branches, (4) length of the frontal branches, (5) length of the parietal branches, and (6) length of the bony tunnel. (A) Main trunk, (B) frontal branches, and (C) parietal branches of the middle meningeal artery

Statistical analysis

The statistical analyses were performed using the SPSS® Statistics(IBM, Chicago, USA). The comparison between the morphometric organization of the right and left MMA from each skull was performed using a paired t-test and data were expressed in mean ± standard deviation; P < 0.05 was considered statistically significant.

RESULTS

In our study on performing paired “t” test, there was a significant difference found between the parameters such as length of frontal (P = 0.034) and parietal (P = 0.023) branches and length of bony tunnel (P = 0.045) of the right and left sides, but there was no significant difference found for angle of main trunk (P = 0.433), angle between frontal and parietal (P = 0.331) branches, and length of main trunk (P = 0.243). On performing Pearson's correlation, there was no significant difference found between the right and left sides of the skull [Table 1].

Table 1

Comparison of the morphometric parameters of the right and left sides of the bone canal for the middle meningeal artery in the skull

Morphologic parameters	Mean±SD (maximum-minimum)		Paired t-test (P)	Pearson’s correlation significance (P)
	Right MMA	Left MMA
Angle of the main trunk (°)	87.6±22.3 (103.5-35.4)	87.2±21.0 (104.3-33.5)	0.433	0.694
Length of the main trunk (mm)	23.9±9.6 (49.5-21.4)	24.8±10.3 (50.3-21.3)	0.243	0.857
Angle between the frontal and parietal branches (°)	68±17.2 (95.0-50.3)	68.5±16.3 (95.4-49.5)	0.331	0.453
Length of the frontal branch (mm)	65.0±12.4 (83.4-53.3)	59.2±13.3 (73.4-52.4)	0.034	0.344
Length of the parietal branch (mm)	49.5±19.3 (66.7-29.6)	58.8±10.2 (65.5-23.7)	0.023	0.577
Length of the bony tunnel (mm)	12.8±4.5 (15.6-3.4)	13.7±9.3 (16.7-5.3)	0.045	0.675

P - Level of significance; SD - Standard deviation; MMA - Middle meningeal artery

DISCUSSION

Although few studies documented by Lasjaunias et al.,[7] Krmpotić-Nemanić et al.,[8] Klisović et al.[9] are available in the medical literature regarding anatomical variations of the MMA, there is still a lack of information on the morphometric variations of the length of the branches, their angles, and the differences between the right and left sides of the skull regarding MMA. According to the study by Plummer's on MMA in 1896, the length of these canals varied from 0.3 to 2.8 cm.[10] Besides this study, several other authors have reported details of a bony canal structure in the skull.[1611] In this study, we found a significant difference in mean lenght of Right (12.8 ± 4.5 mm) and left side (13.7 ± 9.3 mm) of bony canal. In addition, on observation, the bony canal was always located around the pterion, posterior to the coronal suture, and inferior to superior temporal line. Although we have not found differences between the anatomical organization of the right and left MMA for other morphometric parameters such as angle of main trunk, length of main trunk, and angle between parietal and frontal branches, we found significant difference in the length between the right and left sides of the frontal (65.0 ± 12.4 and 59.2 ± 13.3 mm) and parietal branches (49.5 ± 19.3 and 58.8 ± 10.2 mm).

Several studies have been reported that the complex embryology underlying the development of the MMA may give rise to several anomalous origins, courses, and anastomoses involving this vessel.[121314] Reported variants include partial and complete origin of the MMA from ophthalmic artery, which is a frequently encountered anomaly.[15] In addition, the MMA can originate from the extradural or the intracavernous portions of the internal carotid artery, persistent stapedial artery, and rarely ascending pharyngeal artery[15] and/or basilar artery.[1617]

At the 4th–5th week of intrauterine life, dorsal stem of the second arch artery gives stapedial artery from which MMA develops.[18] Stapedial artery after passing through the obturator foramen of stapes to anastomse with the cranial end of the ventral pharyngeal artery. The stapedial artery contains three branches, i.e. mandibular, maxillary, and supraorbital, which distribute along the divisions of the trigeminal nerve. Mandibular and maxillary arteries leave the cranial cavity through the foramen spinosum and the supraorbital branch that supplies the orbit and the intracranial segment of the MMA anteriorly.[1319] At the 7th–8th week of gestation, the proximal part of the stapedial artery involutes and its remnants become tympanic branches of the MMA.[20] Internal maxillary branch of the external carotid artery communicates with the common trunk of the maxillary and mandibular branches of the stapedial artery and incorporates these vessels. The proximal part of the common stem forms the root of the MMA. The distal part of the MMA is derived from the proximal part of the supraorbital artery, which is a branch of the ophthalmic artery.[21] After this complex developmental stage, the MMA enters the floor of the middle cranial fossa through the foramen spinosum. It then passes laterally through a crest in the greater wing of the sphenoid bone, subsequently dividing into frontal and parietal branches.[20] On entering the cranium, the MMA gives off several small branches supplying the trigeminal ganglion and the dura mater, as well as giving rise to superficial petrosal and orbital branches.[22]

We emphasize that our morphological investigation provides innovative and reliable results about the morphometric organization of the right and left MMA. These variations are of clinical significance in preserving the MMA during craniotomy. However, the limitation of our study is less sample size. Thus, we suggest that future studies with larger numbers of subjects will be needed to definitively confirm our findings and may advance the understanding of the development and the contributions of the branches' variations of the normal adult MMA.

CONCLUSIONS

Our study reveals important insights about bilateral anatomical organization of the MMA. Thus, our results undoubtedly will be useful for clinicians, surgeons, and academicians about this arterial segment of the skull that has important clinical interest and finally to help promoting future studies in this area.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.