Variation in human infraorbital nerve, canal and foramen

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Variation in human infraorbital nerve, canal and foramen Jonathan T. Leo, Martin D. Cassell and Ronald A. Bergman Department of Anatomy, College of Medicine, University of Iowa, Iowa City, IA 52242, USA

Summary. In this paper we present a rare case of the infraorbital nerve bifurcating in the base of the orbit, and subsequently passing through two infraorbital canals and exiting by two infraorbital foramina separated from each other by 2 cm in the axial plane and by 1 cm in the sagittal plane. Key words: Infraorbital nerve - Doubled infraorbital foramen - Infraorbital canal - Human

Introduction The maxillary nerve, a purely sensory nerve, arises from the middle of the semilunar ganglion and runs anteriorly in the inferior portion of the cavernous sinus. It exits the cranium by passing through the foramen rotundum, travels through the upper part of the pterygopalatine fossa, and enters the orbit via the inferior orbital fissure (Williams et al. 1989). The nerve, now called the infraorbital nerve, travels anteriorly in the base of the orbit through an infraorbital canal and emerges from the infraorbital foramen onto the face reaching the skin by passing between levator labii superioris and levator anguli oris muscles. The infraorbital nerve can roughly be divided into two parts, one part within the infraorbital canal and the second part being distal to the infraorbital foramen. Within the infraorbital canal the nerve provides three branches: middle superior alveolar arising in the posterior part of the infraorbital sulcus, and usually two anterior superior alveolar nerves which arise in the anterior portion of the infraorbital canal. Once the nerve exits the infraorbital foramen it divides into four branches: 1) inferior palpebral, supplying skin and conjunctiva of the lower eyelid; 2) external nasal, supplying the skin of the vestibule of the nose; Correspondence to: Ronald A. Bergman

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3) internal nasal, supplying the skin of the posterior part of the aspect of the nose; and 4) superior labial, supplying skin of the cheek, upper lip, and labial mucous membrane. Thus, distal to the infraorbital foramen the infraorbital nerve is responsible for the sensory innervation to that part of the face between the lower eyelid and the upper lip (Anson 1966). In an adult male cadaver an infraorbital nerve was found bifurcating within the infraorbital canal into two branches that ran in the base of the orbit and pierced the maxillary bone through two widely separated foramina.

Materials and methods The observations were made on the infraorbital nerve of an embalmed adult Caucasian male cadaver. Dissection followed routine procedures. After skinning, the fascia was removed. In addition the head was bisected and the lateral walls of the nasal cavity were removed to expose the interior of the maxillary sinus. The bone forming the inferior wall of the infraorbital canals was then carefully chipped away to provide access to the nerve.

Results On the right side instead of the usual single infraorbital nerve there were two distinct divisions of the nerve each encased in a separate bony canal. The nerves, roughly equal in size, exited the canals and emerged onto the face through two foramina approximately 2 cm apart (axial plane). The medial foramen was about 1 cm higher (sagittal plane) than the lateral nerve (Fig. 1). The superior of the two nerves was more medial and sent branches to the external nasal surface. The inferior-lateral branch sent twigs to the external nasal surface, the superior portion of the upper lip and small twigs were seen to form a ramus communicans with

branches of the facial nerve. The left infraorbital nerve did not exhibit this variation. It was found in a single infraorbital canal with normal superficial branches.

Discussion These observations, of both a paired infraorbital nerve and two infraorbital canals and foramina are of interest because of their apparent rarity (Bergman 1988) and relevance to anaesthesia of the face. The earliest account of variation in the infraorbital canal is given by Gruber in 1875. Gruber reported that the number of foramina vary in number from 1 to 5. It was however, Kadanoff, Mutafov and Jordanov in 1970, that tabulated and illustrated the variety of infraorbital foramina that were found in over fourteen hundred skulls. Kadanoff et al. found 131 doubled (9%), 7 tripled (0.5OJo) and 4 greater than three (0.3%). Kadanoff et al. provided an illustration to show the position and form of infraorbital foramina seen in their study. In Figure 2, we have added our specimen to those of Kadanoff et al. doubled foramina. Although our specimen is clearly different from those depicted, it does not appear fundamentally different from any that are in the Kadanoff et al. series but rather compliments that series and extends it. Berry (1975) reported accessory infraorbital foramina in skulls from four geographical locations: English, 2.2% in men and 4.8% in women; Burmese, 6.4% in men and 8.7% in women; Americans (Northwest), 12.5% in men and 7.9% in women and Mexican, 18.2OJo in men and 12.5% in women. The number of accessory foramina were not discussed. Two hundred-fifty complete skulls (500 halves) in the Iowa collection did not have more than one foramen per half skull although two were divided by a partition. In 1874 Gruber described the canalis infraorbitalis supernumerarius and the canalis infraorbitalis anomalus externus. This was followed in 1970 by an extensive examination of 1,446 skulls by Kadanoff, Mutafov, and Jordanov. However these studies were conducted on cleaned and dried skulls and lacked therefore specific data concerning the nerves. Jordan (1967) reported the case of a female cadaver

Fig. 1 A. Note the two branches of the infraorbital nerve exiting through separate foramina. The skin and fascia have been removed to expose the nerves. The superior-medial branch supplies the superior external nasal surface. The inferior lateral branch supplies the upper lip, the inferior nasal surface, and also has small twigs anastomosing with the facial nerve. Fig. 1 B. View through the maxillary sinus of the bifurcation of the infraorbital nerve. The maxillary bone forming the base of the orbit has been removed to expose the bifurcation of the nerves proximal to the infraorbital foramina. NS: Nasal septum, HP: Hard palate.

Fig. 2. Diagram of doubled infraorbital foramina by Kadanoff et al. (1970) with the added results of the present study. Note that our case differs from those previously reported. It represents a permutation of those previously reported.

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with a "doubled" infraorbital nerve. The trunk of the maxillary nerve divided into two branches after entering the orbit. Within the orbit the accessory infraorbital nerve gave off branches to the lacrimal sac and two branches to the sinus which supplied the teeth and mucous membrane of the sinus. Jordan's observation of the double nerve in addition to the double foramen is of interest to both the anatomist studying human variation and the clinician who wants to anaesthesize the face. The present case differs from that of Jordan (1967) in two ways: 1) the bifurcated infraorbital nerves were completely contained within bony canals and the two branches of the nerve were of about equal diameter, and 2) they did not supply the same region, hence neither could appropriately be called an "accessory" nerve. In a clinical situation, the variation reported here would be relevant in attempts to anaesthesize that part of the face usually innervated by the maxillary nerve. Since the branches of the infraorbital nerve are usually distal to the foramen, the common practice is to infiltrate local anaesthesia at the foramen resulting in sensory loss to the area between the lower eyelid and the upper lip (Boberg 1980). Clinicians typically locate the foramen by dropping a vertical line from the center of the pupil and palpating 4 - 5 millimeters medial to the line and 5 - 8 millimeters below the lower border of the orbit (DuBrul 1949). However, in the case reported here, some of the sensory areas of the face are innervated by fibers leaving the infraorbital nerve

proximal to the foramen. Thus neural blockade at the foramen would not entirely anaesthesize the predicted area of the face.

References Anson BJ (1966) Morris' Human Anatomy, 12th Ed. McGraw Hill, New York Bergman RA, Thompson SA, Afifi AK, and Saadeh FA (1988) Compendium of Human Anatomic Variation. Urban and Schwarzenberg, Baltimore Berry AC (1975) Factors affecting the incidence of non-metrical skeletal varients. J Anat 120: 519-535 Boberg J, Barber A, and Barber SS (1980) Neural blockade for ophthalmologic surgery. In: Cousins MJ, Bridenbaugh PO (eds) Neural Blockade in Clinical Anesthesia and Management of Pain. JB Lippincott, Philadelphia DuBrul LE (1988) Sieher and DuBrul's Oral Anatomy, 8th Ed. Ishiyaku EuroAmeriea Inc, St Louis Gruber W (1874) Uber die infraorbitalen Kanale des Menschen und der Saugetiere. Mem Acad Imp Sci St Petersburg 21: 1 - 27 Jordan J (1967) Double infraorbital nerve in man. Folia Morphol 26: 405-407 Kadanoff D, Mutafov St, Jordanov J (1970) Uber die Hauptoffnungen resp. Incisurae des Gesichtsschadels. Morph Jb 115: 102-118 Williams PL, Warwick R, Dyson M, Bannister LH (1989) Gray's Anatomy, 37th Ed. Churchill and Livingstone, Edinburgh Accepted January 17, 1994

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