http://www.ijos.org.cn Piagkou et al. Lingual Nerve Entrapment in Muscular and Osseous Structures doi: 10.4248/IJOS10063 REVIEW Lingual Nerve Entrapment in Muscular and Osseous Structures Maria Piagkou*, Theano Demesticha, Giannoulis Piagkos, Androutsos Georgios, Skandalakis Panagiotis Department of Anatomy, School of Medicine, Faculty of Health Sciences, University of Athens, Athens, Greece Abstract Any variations in the course of the lingual nerve can be of clinical significance to surgeons and neurologists because Running through the infratemporal fossa is the lingual of the significant complications that might occur. To name a nerve (i.e. the third branch of the posterior trunk of the few of such complications, lingual nerve entrapment can mandibular nerve). Due to its location, there are various lead to: (a) numbness, hypoesthesia or even anesthesia of anatomic structures that might entrap and potentially the tongue’s mucous glands; (b) anesthesia and loss of taste compress the lingual nerve. These anatomical sites of in the anterior two-thirds of the tongue; (c) anesthesia of the entrapment are: (a) the partially or completely ossified lingual gums; and (d) pain related to speech articulation pterygospinous or pterygoalar ligaments; (b) the large disorder. Dentists should, therefore, be alert to possible lamina of the lateral plate of the pterygoid process; and (c) signs of neurovascular compression in regions where the the medial fibers of the anterior region of the lateral lingual nerve is distributed. pterygoid muscle. Due to the connection between these nerve and anatomic structures, a contraction of the lateral Keywords lingual nerve, compression, pterygospinous pterygoid muscle, for example, might cause a compression ligament, lateral pterygoid muscle of the lingual nerve. Received Jun. 29, 2010; Revision accepted Aug. 23, 2010 Introduction Entrapment of the lingual nerve (LN) takes place when different anatomical structures compress the LN at various points along its course. A typical site of LN compression is the infratemporal fossa (ITF) (Nayak et al., 2008); situated below the middle cranial fossa of the skull, between the pharynx and the ramus of the mandible. This retromaxillary area contains the muscles for mastication, the pterygoid venous plexus, the maxillary artery (MA), and the ramification of the mandibular nerve (MN) (Figure 1) (Prades et al., 2003). Figure 1 Relationship and terminal distribution of The MN descends through the foramen ovale the maxillary artery (MA) and accessory meningeal (FO) into the ITF and, in close relation to the artery in the infratemporal fossa lateral pterygoid muscle (LPt), then which divides TN: trigeminal nerve; ECA: external carotid artery; IAA: into a smaller anterior trunk containing the anterior inferior alveolar artery; ATN: auriculotemporal nerve; MA: deep temporal nerve (ADTN), the posterior deep maxillary artery. Int J Oral Sci, 2(4): 181–189, 2010 - 181 - Lingual Nerve Entrapment in Muscular and Osseous Structures Piagkou et al. http://www.ijos.org.cn temporal nerve (PDTN), and the masseteric nerves numerous dental, oncological and reconstructive that pass between the roof of the ITF and the LPt. procedures (Akita et al., 2001). These variations The posterior trunk, which contains the LN, the can cause serious implications to any surgical inferior alveolar nerve (IAN), and the auriculo- intervention in the region and may lead to a false temporal nerve (ATN), descends medially to the differential diagnosis for a neurological condition. LPt, a site of potential LN entrapment (Isberg et If abnormal branches of the MN were to occur in al., 1987; Loughner et al., 1990). combination with ossified ligaments, then cuta- Occasionally, the FO can be covered by a bony neous sensory fibers might pass through one of the lamina or bridge, which results from ossification foramina formed by the ossified bars (Shaw, 1993). of the ligament between the lateral pterygoid Entrapment of the LN can cause numbness in all process and the sphenoid spine (Kapur et al., regions innervated by it, which could result in loss 2000). Τhe formation of these osseous structures of taste to various extents, and could also generate are, therefore, the outcome of secondary ossifica- pain during speech or other articulatory processes tion in surrounding ligaments (Peuker et al., 2001). (Peuker et al., 2001). Lang and Hetterich (1983) asserted that the pterygospinous bar was present in human skulls as young as 5 years of age, in which adjacent sutures The typical course of the lingual nerve were still evident. From a clinical standpoint, ossified ligaments have become very important when The LN is a major branch of the posterior trunk considering different methods of block anesthesia of the MN at the FO. It begins its course from the for the MN (Lepp and Sandner, 1968). Additionally, ITF running laterally to the MPt, then to the these osseous structures may be implicated in the medial and ventral regions of the IAN (Kim et al., production of various neurological disturbances 2004; Trost et al., 2009). The LN runs between the (Shaw, 1993). For example, Krmpotic-Nemanic et tensor veli palatini and LPt muscles, where it is al. (2001) noted that a pterygospinous foramen then joined by the chorda tympani (CT) branch of replacing the FO could provoke trigeminal neuralgia the facial nerve. The CT innervates taste fibers for (TGN) (Figure 2). the anterior two-thirds of the tongue, as well as parasympathetic fibers for the submandibular and sublingual salivary glands (Zur et al., 2004). The LN proceeds downwards and then forwards along the surface of the MPt, and progresses towards the medial surface of the mandibular ramus until it reaches the bone located a few millimeters below and behind the junction of the vertical and hori- zontal rami of the mandible; thereby lying anteriorly to, and slightly deeper than, the IAN. The LN then passes below the mandibular attach- ment of the superior pharyngeal constrictor and pterygomandibular raphe (closely applied to the Figure 2 Complete pterygospinous osseous bar periosteum of the medial surface of the mandible), and the enlarged pterygospinous foramen on the left until it lies opposite to the posterior root of the side of a male skull third molar; the site whereby it is covered only by M: mandible; LPP: lateral pterygoid plate; FPs: pterygospinous the gingival mucoperiosteum. On the upper end foramen; OC: occipital condyle; ZA: zygomatic arch; SP: styloid level of the mylohyoid line, the LN continues process. horizontally along the superior surface of the mylohyoid muscle, courses in close relation to the Variations in the course of LN are important upper pole of the submandibular gland, and then considerations for effective administration of local releases its fibers to the submandibular ganglion. anaesthesia, as well as for successful outcomes in The LN is closely situated to the posterior part - 182 - Int J Oral Sci, 2(4): 181–189, 2010 http://www.ijos.org.cn Piagkou et al. Lingual Nerve Entrapment in Muscular and Osseous Structures of the sublingual gland and divides into numerous structures. A ligament’s ossification may compress branches entering the tongue’s tissue. The LN first the neighbouring structures and provoke complica- courses along the surface of the styloglossus, then tions in regional surgery (Ozdogmus et al., 2003). along the lateral surface of the hyoglossus and In 1835, Filippo Civinini observed that in some genioglossus, before dividing into terminal bran- cases the lateral pterygoid plate extends pos- ches which supply the overlying lingual mucosa teriorly to contact the base of the spinal process of (Peuker et al., 2001). In addition to receiving the the sphenoid bone. In 1837, Civinini described the CT and a branch from the IAN, the LN is ossification of the pterygospinous ligament in connected to the submandibular ganglion by two varying degrees, as well as the formation of the to three branches and, at the anterior margin of the “Civinini bar” located medial to the FO. The result hyoglossus, it forms connecting loops with fibers was the formation of the pterygospinous foramen, of the hypoglossal nerve. The LN supplies general through which passed the medial pterygoid vessels sensation to the mucosa, the floor of the mouth, and nerves, as well as branches of the MN which the lingual gingival, and the mucosa of the anterior innervate the muscles for mastication (Tebo, 1968; two-thirds of the tongue (an area posteriorly over- Peker et al., 2002). The pterygospinous ligament is lapped by lingual fibers of the glossopharyngeal occasionally replaced by muscular formations, nerve (Rusu et al., 2008). The nerve transfers neural such as the pterygospinous muscle when inserted sensory fibers for general sensitivity (pressure, into the TMJ capsule and extended to the articular temperature, pain, touch) and for taste sensation to disc (von Ludinghausen et al., 2006). the anterior part of the tongue via the CT. The Civinini found complete ossification of the medial and lateral branches of the LN have pterygospinous ligament in 2%–3% of the dry anatomical connections with the hypoglossal nerve skulls examined (Figure 3). in the tongue body. In view of this connection, precise knowledge of the anatomical distribution of the LN may, therefore, assist oral surgeons in executing safe and effective procedures (Zur et al., 2004). The LN can sometimes be entrapped, either through: (a) an ossified pterygospinous or ptery- goalar ligament (located on the outer part of the cranial base); (b) an extremely wide lateral lamina on the pterygoid process of the sphenoid bone; or (c) the medial fibers of the anterior region of the Figure 3 Complete pterygospinous osseous bar on lateral pterygoid muscle (von Ludinghausen et al., the right side of a skull 2006). Recently, it was proposed that some cases M: mandible; FPs: pterygospinous foramen; OC: occipital condyle; of temporomandibular joint syndrome or myo- ZA: zygomatic arch; SP: styloid process. fascial pain syndrome could be a result of nerve entrapment in the ITF (Koppel and Thompson, Other authors reported a prevalence of 3%– 1976).