Introduction:
Maxillary artery is a branch of the external carotid artery supplying a vast
region including the auditory tube, dura mater, the outer and middle ear, the upper and lower jaws, the muscles
of the temporal and infratemporal regions, the nose and paranasal air sinuses, the palate and the root of the
pharynx. It is a larger terminal branch of external carotid artery given off behind the neck of the mandible.
In the infratemporal fossa, its course is divisible into three parts with relation to lateral pterygoid muscle.(1)
While its first or mandibular part lies below the lateral pterygoid muscle, the second or pterygoid part
usually lies superficial or lateral to lateral pterygoid and medial to the temporalis muscle. The third or
pterygopalatine part enters the pterygopalatine fossa by passing between the two heads of the lateral
pterygoid muscle and through the pterygomaxillary fissure. The usual relation of the second part of
the maxillary artery with the lateral pterygoid muscle is variable as in about 29% of cases; the artery lies
deep to the muscle.(2) Many authors have studied the variant pattern of the maxillary artery, but no
consistencies among the reported observations are so far achieved. The peculiar course of maxillary artery
piercing the temporalis muscle that we are publishing herewith is a rare and unique variation. In the present
case, an atypical superficial course of the maxillary artery, piercing the temporalis muscle was noticed.
Such an anomalous course might lead to entrapment of the artery when the muscle contracts and may cause
numbness or headache and may interfere with the injection of local anesthetics into the infratemporal fossa.
This unusual morphology of the maxillary artery should be kept in mind by surgeons performing radical
maxillectomy and endoscopic endonasal surgery for tumors of infratemporal fossa.
Case Report
During routine cadaveric dissection of the infratemporal region for the MBBS
students, we observed a peculiar course of second or pterygoid part of the maxillary artery. The proximal half
of the artery was superficial to the temporalis muscle. It then pierced the temporalis muscle and coursed deep
to it lying lateral to lateral pterygoid muscle (Figure 1). Because of the arterial piercing, the fibers of
temporalis muscle was divided into two parts; superficial anterior and deep posterior parts (Figure 2). The
further course of the maxillary artery towards the pterygopalatine fossa through the pterygomaxillary
fissure was unremarkable. No variations in the branching pattern and other relations of the artery were
found. This variation was observed on the left infratemporal fossa of a male cadaver aged about 60 years.
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Figure 1: Dissection of the left infratemporal region showing maxillary artery (MA) piercing the temporalis muscle (TM). MM- Masseter (reflected anteriorly), RM- ramus of the mandible, EAM- external acoustic meatus, IAVN- inferior alveolar vessels and nerve
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Figure 2: The closer view [A] showing the division of temporalis muscle (TM) being pierced by the maxillary artery (MA) superficial to deep. The schematic representation of the present case is shown in [B]. MM- Masseter (reflected anteriorly), IAVN- inferior alveolar vessels and nerve, ECA- external carotid artery. |
Discussion
The infratemporal fossa is a complex anatomical area on the face that is affected by benign
and malignant tumors. Comprehensive anatomical knowledge of the variant course of the maxillary artery is essential in
choosing the best approach for treating lesions in this area.(3) Conventionally, the maxillary artery is classified into
three types concerning its relation to lateral pterygoid muscle. The lateral type of the maxillary artery runs laterally
to the lateral pterygoid muscle, the intermediate type of the artery runs through the lateral pterygoid and in medial type,
it courses medially to the muscle. Following the presence of multiple patterns of variant course of maxillary artery Maeda
et al., proposed an extended categorization to this primary type of classification.(4) According to them, the lateral type
of maxillary artery can be further divided into group A and group B categories based on its relation to temporalis muscle.
In group A, maxillary artery pierces the temporalis muscle, whereas in group B it does not pierce the temporalis muscle
(Figure 3). Among 104 cadavers (208 sides) examined in their study, no single case of group A maxillary artery was
identified in contrast to 90.4% of group B cases. Though the present case is of group A category, the pattern of piercing
the muscle is different. (Figure 2B).
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Figure 3: Schematic representation of Group A and Group B category of lateral type of maxillary artery according to Maeda et al (4) description.
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Reports on the rare course of maxillary artery coursing through the nearby nerves of the infratemporal region, such as
through the two roots of auriculotemporal nerve (5) and through the inferior alveolar nerve (6) are available in scientific
literature. Abnormal passage of the artery through the nerve loop formed between auriculotemporal nerve and posterior division
of mandibular nerve (7) and between the lingual nerve and trunk of mandibular nerve (8) are also reported.
A limited number of cases of maxillary artery piercing through the temporalis muscle at its superficial course is reported.
(9,10) Patil et al. reported the complete intramuscular course of the maxillary artery through the substance of temporalis
muscle and stated that the second part of the maxillary artery is liable to the variant course than its other parts.(11)
Claire et al. has reported maxillary artery bifurcating into superficial and deep branches with the eventual reunion to form
a complete loop in the infratemporal region.(12)
In the present case, very superficially coursed maxillary artery piercing the temporalis muscle and separating its muscle
fibers into superficial anterior and deep posterior parts is a unique representation. The embryological basis for such variant
course of the maxillary artery can be accredited to its initial vascular network ring formation adjoining the soft tissue
structures in the developing infratemporal fossa. The eventual persistence of some of its parts may be responsible for the
resultant atypical course of the artery.(12)
Abnormal course of the maxillary artery within the infratemporal region is vulnerable to iatrogenic injury as the fossa is
a clinically important anatomical area for local anesthetic procedures in dentistry and maxillofacial surgery.(6) Vascular
variations in the region of infratemporal fossa can also result in failure of inferior alveolar nerve block and intravascular
injection procedures. From the reported literature, it has been estimated that 20% is the prevalence rate of arterial
penetration during mandibular block.(13)
Conclusion
The very superficial course of maxillary artery in the infratemporal fossa, piercing the temporalis muscle is a rare
variation. Due to this anomalous course, the artery might get compressed by the contraction of the muscle during mastication
and affect the blood flow through it. Such variations should be kept in mind by surgeons performing radical maxillectomy and
endoscopic endonasal surgery for tumors of infratemporal fossa.
Acknowledgment
We acknowledge Mr. Ganesh N
Prasad, Artist, Department of Pathology, Kasturba Medical
College, Manipal, for the schematic diagram.
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