The infratemporal fossa is often the site of pathology or surgical intervention. We describe an unusual muscle found during the routine dissection of the right infratemporal fossa. The literature germane to this variable muscle, best described
as a variant of the pterygoideus proprius, is reviewed. The clinician may
contemplate the wide array of muscular anomalies within the infratemporal fossa
when considering unexplained neurological symptoms attributed to branches of V3 and pursue appropriate diagnostic testing

Loukas, M.

Oakes, W.J.

Salter, E.G.

Shoja, M.M.

Stetler, W.

Tubbs, R.S.

English

Via Medica Journals

Folia Morphol. Vol. 66, No. 3, pp. 200–202Copyright © 2007 Via MedicaISSN 0015–5659www.fm.viamedica.plC A S E   R E P O R T200Address for correspondence: Dr. R.S. Tubbs, Pediatric Neurosurgery, Children’s Hospital, 1600 7th Avenue South ACC 400, Birmingham,Alabama 35233, USA, tel: 205 939 9914, fax: 205 939 9972, e-mail: rstubbs@uab.eduAn unusual muscular variation of theinfratemporal fossaR.S. Tubbs1, 6, W. Stetler2, M.M. Shoja3, M. Loukas4, 5, E.G. Salter1, W.J. Oakes61Department of Cell Biology, University of Alabama at Birmingham, USA2School of Medicine, University of Alabama at Birmingham, USA3Tuberculosis and Lung Disease Institute, Tabriz University, Tabriz, Iran4Department of Anatomical Sciences, St. George’s University, Grenada, West Indies5Department of Education and Development, Harvard Medical School, Boston, Massachusetts, USA6Section of Pediatric Neurosurgery, University of Alabama at Birmingham, USA[Received 16 February 2007; Revised 19 June 2007; Accepted 19 June 2007]The infratemporal fossa is often the site of pathology or surgical intervention.We describe an unusual muscle found during the routine dissection of the rightinfratemporal fossa. The literature germane to this variable muscle, best de-scribed as a variant of the pterygoideus proprius, is reviewed. The clinician maycontemplate the wide array of muscular anomalies within the infratemporal fossawhen considering unexplained neurological symptoms attributed to branchesof V3 and pursue appropriate diagnostic testing.Key words: anatomy, head, V3INTRODUCTIONThe infratemporal fossa is of great interest to cli-nicians and houses important structures such as themandibular nerve and the maxillary artery. This re-gion also contains several of the muscles of mastica-tion derived from a common embryologic source [2].The temporalis, lateral and medial pterygoids, andthe masseter are all derived from a common muscu-lar sheet from the first pharyngeal arch, and are allassociated with the temporomandibular disc duringembryologic development [5]. Owing to their com-mon lineage and rearrangement during development [5],many smaller muscles and tendons have been de-scribed within the infratemporal fossa, representingdevelopmental anomalies and possibly clues to thephylogeny of this region.The pterygoideus proprius was first described byHenle in 1858 [4]. This structure has been describedas originating from the anterior infratemporal crest,running vertically down to insert on the lateral ptery-goid plate and crossing superficially to the lateralpterygoid muscle. Henle also described a distinctiveband of fibers he termed the “temporalis minor” thatarose from the anterior aspect of the (greater) tem-poralis muscle and inserted onto the mandibularnotch instead of the coronoid process [2]. Similarly,Akita et al. [1] noted the presence of an aberrantband of muscle arising from the anteromedial as-pect of the temporalis and interdigitating withfibers from the lateral pterygoid. Such fibromuscu-lar bands are often given a nomenclatural descrip-tion within the greater context of the pterygoideusproprius name. In this report, we describe a similarmuscular finding and note its relationship to the sur-rounding clinically relevant structures. Some haveheld the view that such variations may result in en-trapment or compression of the mandibular nervewith resultant trigeminal neuralgia [6].CASE REPORTWe report an unusual muscular variation withinthe right infratemporal fossa found, upon deep dis-section, in a 73-year-old male cadaver during ananatomy course at the University of Alabama at201R.S. Tubbs et al., An unusual muscular variation of the infratemporal fossaFigure 1. Cadaveric view of the right variant of the pterygoidus proprius muscle (arrows). Note the distal maxillary artery (M) crossingdistally to this muscle. For reference, the lateral pterygoid (L), inferior alveolar nerve (IA) and lingual nerve (LN) are shown.Birmingham. The dissection revealed the presence ofa pterygoideus proprius-like muscle originating fromthe anterior aspect of the infratemporal crest (super-ficial to the fibers of the lateral pterygoid muscle) ofthe greater wing of the sphenoid bone toward theinferior orbital fissure, running inferiorly to insert ontothe pyramidal process of the palatine bone and fus-ing with fibers of the inferior part of the medial ptery-goid muscle (Fig. 1). This structure was partially ten-dinous and partially muscular. The dimensions of thismuscle were approximately 3.5 × 1.5 cm. No nerveinnervation to this muscle was identified. The con-tralateral side of this cadaver had no such anomalousmuscle.This aberrant muscle was mostly consistent withthe original description that Henle gave of the ptery-goideus proprius. However, this structure seems alsoto have fibers that mesh with the lateral pterygoidnear its origin, as well as the medial pterygoid mus-cle near the latter’s insertion onto the ramus of themandible. Also of note and differing from the classi-cal description is a partial insertion onto the infratem-poral surface of the maxilla near the angle of thelateral pterygoid plate, thereby providing a connec-tion between the two structures.  Such a descriptionmost closely relates this structure to the pterygos-pinous structure described by Bergman et al. [2].This variant muscle ran deep to the maxillary ar-tery (Fig. 1). The lingual and inferior alveolar nervescoursed superficially to the connecting meshworkof the pterygoideus proprius-like muscle and themedial pterygoid and posterolaterally to the verti-cal, fibromuscular part of this muscle.DISCUSSIONKnowledge of the contents of the infratemporalfossa is of importance for any surgical procedure inthe area, such as repair of the maxillary artery, aswell as for greater understanding of the embryolog-ic development of the first pharyngeal arch. Studyof the pterygoideus proprius can help shed light onboth these issues.The infratemporal muscles of mastication differ-entiate from common muscular anlagen [1, 2, 5].Penhall et al. [5] offer two hypotheses for the dif-ferentiation of the pterygoideus proprius from theinfratemporal embryological musculature. The firsthypothesis suggests that the pterygoideus origi-nates from the temporalis muscle early in develop-ment before the coronoid process of the mandibleis fully developed for the insertion of the masseterand temporalis muscles. Thus, without a properlocation to insert, some of the temporalis fibers mayattach to the lateral pterygoid plate, thereby ex-cluding them from their host muscle. A second hy-pothesis is that this muscle derived from the lateralpterygoid and that during its differentiation someof its fibers failed to insert onto the developing tem-poromandibular disc, which develops independentlyand later than this muscle. These fibers could thenfall inferiorly and elongate to insert onto the lateralpterygoid plate.202Folia Morphol., 2007, Vol. 66, No. 3Akita et al. [1] have suggested that the embryo-logic precursors to the muscles of mastication maybe divided into a medial group, consisting of themedial pterygoid, and a lateral group, consisting ofall the other muscles of mastication. The aberrantmuscle we describe gives further evidence of a com-mon embryologic origin with differentiation upondevelopment to give separate muscles because thestructure described links the two separated groupsas described by Akita et al. [1], implying a single or-igin. This finding connecting the two developmen-tal groups is consistent with the muscle describedby Akita et al. [1] as connecting the temporalis withthe lateral pterygoid, which was noted as possiblyrepresenting an intermediary vestige.The functionality of the pterygoideus proprius-like muscle as described herein is purely speculative,but it has been proposed that the pterygoideus pro-prius muscle has a role in thermoregulation [5]. Whencontracted, this muscle could feasibly help propelblood from the pterygoid venous plexus, which is inpart between the lateral pterygoid muscle and thepterygoideus, to the cavernous sinus via the smallconnecting vessel that courses through the foramenovale. This action would possibly surround the inter-nal carotid artery carrying warm arterial blood tothe brain parenchyma with fresh, cooler venousblood from the nasal mucosa and face, thereby de-creasing the temperature of the blood in the carotidas heat moves down the temperature gradient [3].The purpose of the unusual pterygoideus we describecould help with the action of mastication or at leastaid in stabilizing the mandible for mastication asa result of to its connections to the medial and later-al pterygoids; however, this too is only speculation.Akita et al. [1] noted direct innervation by the ante-rior deep temporal nerve (V3) of their reported ab-errant muscle, providing additional evidence of thefunctionality of the pterygoideus with contraction.We did not observe any nerve entering the muscledescribed in the present report.Perhaps more important than contraction is theability of a predominantly fibrous structure to ossi-fy with age and impinge upon nearby structures.Bergman et al. [2] report that a fibrous band, termedthe “pterygospinous ligament”, with connectionsbetween the medial and lateral pterygoid muscles,has potential for ossification. Similarly, a predomi-nantly fibrous pterygoideus-like muscle could po-tentially ossify and impinge on branches of V3 cours-ing nearby. The aberrant muscle described in thisreport could potentially impinge upon either thelingual or inferior alveolar branches or possibly evenact as a point of compression for the maxillaryartery or its nearby branches. This muscle addition-ally brought the maxillary artery to a more superfi-cial position, which could predispose this vessel toiatrogenic injury. The clinician may contemplate thewide array of muscular anomalies within the in-fratemporal fossa when considering unexplainedneurological symptoms attributed to branches ofV3 and may then pursue appropriate diagnostictesting [6].REFERENCES1. Akita K, Shimokawa T, Sato T (2001) Aberrant musclebetween the temporalis and the lateral pterygoidmuscles: M. ptergyoideus proprius (Henle). Clin Anat,14: 288–291.2. Bergman RA, Afifi AK, Miyauchi R (1984) Catalog ofhuman variation. Urban & Schwarzenberg, Baltimore.3. Dean MC (1988) Another look at the nose and the func-tional significance of the face and nasal mucous mem-brane for cooling the brain in fossil hominids. J HumEvol, 17: 715–718.4. Henle J (1858) Handbuch der systematischen Anatomiedes Menschen. Friedrich Vieweg und Sohn, Braunsch-weig, pp. 161–164.5. Penhall B, Townsend G, Tomo S, Nakajima K (1998)The pterygoideus propius muscle revisited. Clin Anat,11: 332–337.6. Shimokawa T, Akita K, Sato T, Ru F, Yi SQ, Tanaka S(2004) Penetration of muscles by branches of the man-dibular nerve: a possible cause of neuropathy. ClinAnat, 17: 2–5.

An unusual muscular variation of the infratemporal fossa

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An unusual muscular variation of the infratemporal fossa

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