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Clinical Anatomy 17:667– 671 (2004) CASE REPORT Triplication of the Lesser Occipital Nerve C. MADHAVI AND S.J. HOLLA* Department of Anatomy, Christian Medical College, Tamil Nadu, India Triplication of the lesser occipital nerve (LON) was observed bilaterally in an adult male cadaver during routine prosection of the posterior triangle. The three LONs were studied to determine the clinical importance of this variation. The origin of one LON was from a nerve to the trapezius that had a common origin with the trunk of the supraclavicular nerve (C3,4) from the cervical plexus. Such a common origin of a LON may explain the pain referred to the shoulder and arm that is experienced by some patients with cervicogenic headache. Another LON ran across the roof of the posterior triangle, passed through the trapezius and was closely related to the point of exit of the greater occipital nerve (GON) from the trapezius. This LON supplied the nape of the neck, back of the scalp and the auricle. The anomalous course taken by this LON through the trapezius may be an explanation for cervicogenic headache precipitated by neck movement. The close relationship of this variant LON to the exit of the GON from the trapezius seems to be relevant to the management of cervicogenic headache. The authors suggest that the reason for the complete pain relief experienced by some patients with cervicogenic headache by anesthetic blockade of the GON may be because both the GON and LON are blocked simultaneously due to their proximity in these patients. Clin. Anat. 17:667– 671, 2004. © 2004 Wiley-Liss, Inc. Key words: anomalous course; cervicogenic headache; anesthetic blockade; cervical segments C2– 4 INTRODUCTION The LON normally has a variable origin either from the 2nd or 2nd and 3rd cervical ventral rami. The LON then curves around the accessory nerve and ascends along the posterior border of the sternocleidomastoid, and pierces the deep fascia near the cranium to supply the skin over the scalp and the auricle. The GON is the medial branch of the second cervical dorsal ramus. Whether the LON is involved in cervicogenic headache is controversial. Cervicogenic headache is the term used by Sjaastad et al. (1983) to describe a distinct type of headache of cervical origin with unclear etiology. They studied a group of patients who could provoke headaches by certain head and neck movements. They deﬁned cervicogenic headache as a unilateral headache of moderate intensity, with relatively rare and long-lasting attacks. During the attacks the patients usually have stiffness and pain in the neck, neck movements are restricted and associated with crepitation. In some patients there may be ipsilateral shoulder, arm, and hand pain. Most patients are able to provoke attacks by certain acts, e.g., move© 2004 Wiley-Liss, Inc. ments of the neck, coughing, sneezing, and bowel movements, and also by pressure over the C2 root, over the GON, and over the transverse process of C4-C5 on the symptomatic side. Headaches are associated with ipsilateral phenomena such as blurring and reduced vision, slight lacrimation, conjunctival injection, runny nose, and erythema of the forehead or temporal region. Sometimes patients complain of dizziness, difﬁculty in swallowing, nausea, loss of appetite and occasionally even vomiting during attacks. The pain is mainly in the temporal, frontal, and ocular areas, with pain sometimes in the face. The mean age of onset is 29 years and there is a female preponderance. There may be a previous history of neck trauma. Fredriksen et al. (1987) further deﬁned the clinical manifestations of cervicogenic headache. Typically at*Correspondence to: Dr. Sunil J. Holla, Department of Anatomy, Christian Medical College, Vellore 632 002, Tamil Nadu, India. E-mail: [email protected] Received 1 May 2003; Revised 4 September 2003 Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ca.10252 668 Madhavi and Holla tacks last for 1–3 days with a pain-free interval of 1– 4 weeks and the pain involved the neck and the nape of the neck. In most patients the pain was constantly boring and in none of the patients did the pain have a typical radiating character. Most patients experienced phonophobia and a general feeling of irritability with the attack and did not seem to experience much relief with pain medication such as non-steroidal anti-inﬂammatory agents and ergotamine. There was no signiﬁcant past history or family history of migraine in most patients. Various structures in the neck were implicated as possibly being involved in the etiology of cervicogenic headache such as C1, C2, or C3 root ﬁbers, the occipital nerves, the uncovertebral joints, and the vertebral artery. Hogan and Abram (1997) mentioned that there is a lack of a pathophysiologic understanding of cervicogenic headache and the typical lack of sensory deﬁcit in the area of distribution of the GON does not support a neuropathic mechanism. Alternately, it is possible that pain radiating in the distribution of the GON represents converging deep somatic input from the lateral atlanto-axial joint, which is innervated by the C2 anterior ramus, or from irritation of suboccipital muscles and periosteum, which has been shown to produce ascending headache. The role of the LON in cervicogenic headache has not been emphasized in the aforementioned three articles that deal with cervicogenic headache. In the context of local anesthetic blockade of the GON and LON, Sjaastad et al. (1986) were of the opinion that even though compression of the GON as it passes through the trapezius may be of pathogenetic signiﬁcance, the primary fault might be lower in the neck, where there may be some anatomic misalignment. They suggested certain theoretically possible causes of cervicogenic headache such as cervical spondylosis, uncovertebral arthritis, and vascular malformations along the C2/C3 roots. It has been considered as a matter of debate, however, whether entrapment of the GON in the pertinent muscles might cause headache (Becser et al., 1998). The GON has been implicated as one of the structures involved in cervicogenic headache because anesthetic blockade of the GON relieved the pain in many patients with cervicogenic headache (Sjaastad et al., 1983). The LON also has been implicated in cervicogenic headache (Raffaelli et al., 1987; Lucas et al., 1994). This study describes an anomalous lesser occipital nerve. The anatomical features observed in this case might explain the simultaneous involvement of both the GON and the LON in cervicogenic headache. Fig. 1. Posterolateral view of head and neck showing triplication of the lesser occipital nerve (LON). A, great auricular nerve; Ac, Accessory nerve; E, external jugular vein; G, greater occipital nerve (GON); S, supraclavicular nerve; ST, sternocleidomastoid; T, cervical nerve to trapezius; TR, trapezius; I, LON-I; II, LON-II. Arrowheads: LON-III. CASE REPORT During routine prosection of the head and neck for teaching ﬁrst year MBBS students an anomaly of the LON was observed bilaterally in an adult male cadaver. Careful dissection of the posterior triangle showed three nerves, referred to as the LON I, II, and III that supplied the area that is normally innervated by the LON (Fig. 1). At the middle of the posterior border of the sternocleidomastoid various nerves were seen to emerge and run in different directions. The spinal accessory nerve was found to run parallel to the levator scapulae from the posterior border of the sternocleidomastoid to the anterior border of the trapezius. The great auricular nerve hooked around the posterior border of the sternocleidomastoid 1 cm below the accessory nerve. Midway between these two nerves, a slender nerve (LON-I) hooked around the Triplication of Lesser Occipital Nerve posterior border of the sternocleidomastoid, coursed upwards superﬁcial to this muscle and the mastoid process, and crossed the superior nuchal line. It was distributed to the retroauricular and posterolateral aspects of the occiput. At the posterior border of the sternocleidomastoid, about 3 cm below the exit of the accessory nerve, a nerve emerged that ended by forming the supraclavicular nerve trunk and a branch to the trapezius. The branch to the trapezius gave rise to a slender branch (LON-II) that ascended along the posterior border of the sternocleidomastoid lying parallel to LON-I. This nerve also was distributed to the retroauricular and posterolateral aspects of the occiput. It passed over the mastoid process but did not extend beyond the superior nuchal line. It had a slender communication with LON-I. The LON-III, thicker than the other two LONs, emerged at the posterior border of the sternocleidomastoid superior to the accessory nerve and running a sinuous course across the posterior triangle the LONIII passed deep to the trapezius (Fig. 1). The LONIII then ascended superomedially for 2 cm, passing deep to the lateral-most fascicles of the trapezius and pierced this muscle in a fascial cleft 3 cm below the superior nuchal line and 3.5 cm lateral to the midline. The GON and the occipital artery also pierced the trapezius in the same fascial cleft at a point 2 cm superior to the exit of the LON-III from the trapezius and 3.5 cm lateral to the midline. After piercing the trapezius the LON-III ran superolaterally superﬁcial to the lateral fascicles of the trapezius on the subocciput and divided into two branches below the superior nuchal line. The lateral branch arched forward and was distributed to the upper third of the cranial surface of the auricle. The medial branch ran superior to the lateral branch and was distributed to the occiput. The LON-III was distributed to the nape of the neck, occiput, and the upper third of the cranial surface of the auricle. Its area of innervation partly overlapped that of the GON in the scalp. The GON was normal and was distributed to the medial half of both the subocciput and occiput. DISCUSSION Normally a single LON supplies the posterolateral aspect of the neck and scalp and the cranial surface of the upper part of the auricle. Duplication of the LON has been reported, where the lateral nerve supplied the retroauricular region, whereas the medial nerve supplied the adjacent scalp (Romanes, 1987; Lucas et al., 1994; Berry et al., 1995; Becser et al., 1998). 669 Triplication of the LON has not been reported. In the present case, there were three distinct LONs. Two of these (LON-I and II) were slender nerves following the normal course in relation to the sternocleidomastoid muscle and supplying the retroauricular and posterolateral aspect of the occiput. The LON-II had a common origin with the cervical nerve to trapezius and the supraclavicular nerve trunk; both of which came from ventral rami. This common origin may result in a contribution of C3 ﬁbers to the LONII. The shoulder and arm pain felt by some patients with cervicogenic headache (Sjaastad et al., 1983) might have resulted from the presence of a common origin for the LON, supraclavicular nerves and cervical nerves to trapezius, as in the present case. The explanation for this referred pain may be altered central processing of nociceptor information at the level of the second order neurons as highlighted in a similar situation by Kinney et al. (2003). The LON-III and the GON pierced the same ﬁbrous tissue that separated the lateral fascicles of the trapezius from the rest of the muscle (Fig. 1). The complete relief of pain experienced in patients with cervicogenic headache by anesthetic blockade of the GON (Sjaastad et al., 1986) may have been due to the presence of a LON close to the GON (as in the present case) that was also blocked. Patients who had incomplete pain relief might have had a LON outside the site of the block. Reasons for the inefﬁcacy of local blocks of the GON have been described, and it has been reported that variations and communications with other nerves could have an impact on the efﬁcacy and extent of LON blockade (Becser et al., 1998). Pantaloni and Sullivan (2000) reported that in 5 of 19 cadaver dissections the LON supplied the superior two-thirds of the ear (rather than the superior onethird that is usually described), and highlighted the importance of this variation in facial rejuvenation surgery. Sjaastad et al. (1986) carried out more than 40 diagnostic anesthetic blockades of the GON in patients with suspected cervicogenic headache, and reported incomplete pain relief in some cases. Austad (2000) surgically treated about 300 patients with occipital neuritis and described the location for occipital block as a horizontal band approximately 2 cm long over the insertion of the trapezius and centered approximately 4 cm from the midline. He noted that in 30 – 40% of his patients the greater occipital artery seemed to signiﬁcantly compress the GON and about 30% of his patients had perineural lymph nodes that seemed to be causing extraneural compression at or near the exit of the GON from the trapezius. He carried out decompression of the GON at the point where the nerve passed through the trapezius. He 670 Madhavi and Holla reported that approximately one-third of his patients dramatically improved after surgery for occipital neuritis. Hunter and Mayﬁeld (1949) suggested the vulnerability of the anterior and posterior primary rami of C2 to trauma between the atlas and axis and this has been emphasized recently (Kinney et al., 2003). Kerr and Olafson (1961) suggested that the convergence of trigeminal and cervical dorsal root afferents to the same area of the upper cervical spinal segments might be a basis for spread of hemicranial pain from cervical to trigeminal areas. Becser et al. (1998) mentioned that anatomic variants in the periphery combined with such mechanisms as compression, stretch, trauma or inﬂammation may be important in the pathogenesis of cervicogenic headache, and that the combination of various factors may be necessary for pain production, at least in some cases. Hogan and Abram (1997) have emphasized that there are various limitations and interpretations of nerve blocks. They mentioned that because all the proposed pathophysiologies of cervicogenic headache are unproved, the meaning of various blockade responses do not rest on a solid mechanistic base. In addition, the therapeutic plan is not well deﬁned after a favorable response to test injections, and the ability of GON blockade to identify patients with disease is hampered by an inexact deﬁnition of cervicogenic headache and no means of conﬁrmation. They also stated that most studies, as well as the deﬁnition of the condition, come from a single group of authors. The position of emergence of the LON and the GON in the ﬁbrous tissue partition between the lateral muscle fascicles and the rest of the trapezius might make it vulnerable to compression and stretching. Relief by surgical release of clinical manifestations of nerve compression by a tendon have been reported (Spinner et al., 1996). It is controversial whether there is clinical evidence of the involvement of the LON in cervicogenic headache (Raffaelli et al., 1987; Lucas et al., 1994). If the LON is involved, it may be due to entrapment neuropathy of the LON as it passed through the trapezius. Because dermatomes of adjacent spinal segments overlap markedly (Berry et al., 1995), the involvement of the GON (C2) may manifest in the of cutaneous area innervated by the LON (C2,3). Lucas et al. (1994) noted that the area described for the dermatome of C2 comprises the region supplied by the GON, and the dermatome of C3 occupies areas innervated by the LON, great auricular nerve and the transverse cervical nerve. Fredriksen et al. (1987) noted that the characteristic pain of an attack of cervicogenic headache could be precipitated by ﬁrm manual pressure directed to four “trigger” points: midway between the external occip- ital protuberance and the mastoid process; C2 area, that is behind and just below the mastoid process, and the transverse processes of C4 and C5. Lucas et al. (1994) have pointed out that the ﬁrst two of these points are sites that are anatomically occupied by the LON. The anatomical peculiarities of the LON observed in the present case, such as its anteroposterior course across the posterior triangle and the manner of exit from the trapezius may be an explanation for the precipitation of cervicogenic headache by neck movement in some patients. Basmajian and Slonecker (1989) refer to the part of the posterior triangle superior to the accessory nerve as the “carefree part,” where there is no important structure in the fascial roof. Lucas et al. (1994) have reported an anomalous course taken by the LON in 6 of 16 dissections, in the region where the nerve ascended to the occipital region lying between the posterior border of the sternocleidomastoid and the lateral border of the trapezius. In the present case the thickest of the three LONs, the LON-III, stretched anteroposteriorly across the roof of the posterior triangle extending from the posterior border of the sternocleidomastoid to the lateral border of the trapezius (Fig. 1). These cases indicate that the superior part of the posterior triangle is not always a “carefree part.” Awareness of variations in the course of the LON can help to prevent inadvertent injury to it during surgery of this region. 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