Journal of Clinical Neuroscience 32 (2016) 83–87

Contents lists available at ScienceDirect

Journal of Clinical Neuroscience

journal homepage: www.elsevier .com/ locate/ jocn

Clinical Study

Modified skin incision for avoiding the lesser occipital nerve andoccipital artery during retrosigmoid craniotomy: potential applicationsfor enhancing operative working distance and angles while minimizingthe risk of postoperative neuralgias and intraoperative hemorrhage

http://dx.doi.org/10.1016/j.jocn.2016.03.0150967-5868/� 2016 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +1 317 362 8760; fax: +1 317 924 8472.E-mail address: acohenmd@gmail.com (A.A. Cohen-Gadol).

R. Shane Tubbs a,b,c, Fabian N. Fries d, Charles Kulwin e, Martin M. Mortazavi f, Marios Loukas b,Aaron A. Cohen-Gadol e,⇑a Seattle Science Foundation, Seattle, WA 98122, USAbDepartment of Anatomical Sciences, St. George’s University, GrenadacCentre of Anatomy and Human Identification, University of Dundee, DD1 4HN, Scotland, UKd Saarland University Medical Center and Saarland University Faculty of Medicine, D66424 Homburg, GermanyeGoodman Campbell Brain and Spine, Department of Neurological Surgery, Indiana University School of Medicine, 355 W. 16th Street, Suite #5100, Indianapolis, IN 46202, USAfCalifornia Brain Institute, Los Robles Hospital and Medical Center, Thousand Oaks, CA 91360, USA

a r t i c l e i n f o

Article history:Received 15 March 2016Accepted 22 March 2016

Keywords:AnatomyLesser occipital nerveNervesOcciputRetrosigmoid craniotomy

a b s t r a c t

Chronic postoperative neuralgias and headache following retrosigmoid craniotomy can be uncomfortablefor the patient. We aimed to better elucidate the regional nerve anatomy in an effort to minimize thispostoperative complication. Ten adult cadaveric heads (20 sides) were dissected to observe the relation-ship between the lesser occipital nerve and a traditional linear versus modified U incision during retrosig-moid craniotomy. Additionally, the relationship between these incisions and the occipital artery wereobserved. The lesser occipital nerve was found to have two types of course. Type I nerves (60%) remainedclose to the posterior border of the sternocleidomastoid muscle and some crossed anteriorly over thesternocleidomastoid muscle near the mastoid process. Type II nerves (40%) left the posterior border ofthe sternocleidomastoid muscle and swung medially (up to 4.5 cm posterior to the posterior border ofthe sternocleidomastoid muscle) as they ascended over the occiput. The lesser occipital nerve was neara midpoint of a line between the external occipital protuberance and mastoid process in all specimenswith the type II nerve configuration. Based on our findings, the inverted U incision would be less likelyto injure the type II nerves but would necessarily cross over type I nerves, especially more cranially onthe nerve at the apex of the incision. As the more traditional linear incision would most likely transectthe type I nerves and more so near their trunk, the U incision may be the overall better choice in avoidingneural and occipital artery injury during retrosigmoid approaches.

� 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Retrosigmoid craniotomy is a standard approach used by theneurosurgeon. Some patients have significant headaches followingretrosigmoid craniotomy. Such a complication has also been foundto affect postoperative quality of life in these patients [1]. Postop-erative headache following retrosigmoid craniotomy is a well-known entity and although multifactorial, may be due to occipitalnerve transection, entrapment, or neuroma formation.

The lesser occipital nerve is classically described as arising fromcervical two (C2) and C3 ventral rami and then courses around theposterior and deep surface of the sternocleidomastoid to ascendparallel with the muscle’s posterior border. Occasionally, the nervemay pierce the sternocleidomastoid muscle. Near the cranium, thelesser occipital nerve perforates the deep fascia and passes up intothe scalp around the auricle to supply the skin and connect withthe great auricular and greater occipital nerves and auricularbranch of the facial nerve [2,3]. The nerve also supplies an auricularbranch, which supplies sensory innervation to the upper and med-ial thirds of the auricle. This branch also communicates with theposterior branch of the great auricular nerve.

84 R.S. Tubbs et al. / Journal of Clinical Neuroscience 32 (2016) 83–87

Compression or stretching of the lesser occipital nerve mayresult in cervicogenic headaches or occipitoparietal migraines, thusthe lack of a definitive nerve blockade site makes it difficult to treatthese headaches [1].

The senior author (A. C-G.) has been using the reverse ‘‘U” inci-sion (Fig. 1) for retrosigmoid craniotomy as described by Dandy [4]for the past 3 years and has noted a decreased rate of postoperativeheadaches and more specifically occipital pain among his patients.Therefore, we performed the current cadaveric study to better elu-cidate the regional anatomy and to compare this incision with themore typical linear incision in regard to regional neurovascularbundles. The advantages of the ‘‘U” incision for improving theoperative working distance and angles will also be reviewed.

2. Materials and methods

For the present study, 10 adult formalin-fixed cadaveric heads(20 sides) were used. These specimens were derived from five maleand five female adult cadavers with an average age at death of63 years (range 55 to 79 years). In the prone position, the subcuta-neous tissues of the posterior head and upper cervical spine, fromposterior to the pinna to approximately 2 cm lateral to the midlinewere dissected. The relationship between the lesser occipital nervein the region where a standard retrosigmoid craniotomy would beperformed was observed. Specifically, the relationship with the les-ser occipital nerve to a traditional linear and modified U incisionwas recorded.

Fig. 1. Schematic drawing of the positioning of a craniotomy for left-sidedretrosigmoid approaches. The dotted white line connects the root of the zygomaand the inion and marks the level of the transverse sinus. The vertical blue line isthe mastoid groove. The junction of these two lines is the summit of the incisionand approximates the junction of the transverse and sigmoid sinuses. [Withpermission from The Neurosurgical Atlas by Aaron Cohen-Gadol, MD] [30].

The 7 cm linear incision was localized 0.5 cm posterior and par-allel to the mastoid groove and one third above and two thirdsbelow the transverse sinus. The curvilinear incision was deter-mined as follows: A line connecting the inion to the root of zygomawas marked. The junction of this line with extension of the linemarking the mastoid groove was noted as the summit of the inci-sion. A wide-based curvilinear ‘‘U” incision dependent on this sum-mit was marked (Fig. 1). Relationships between the linear andmodified incision and the occipital artery were also observed. Allmeasurements were made with digital calipers (Mitutoyo, Japan).No specimen was found to have prior surgery or gross injury tothe areas dissected. Statistical analysis between sides and sexwas performed using Statistica for Windows (Dell; Tulsa, OKUSA) with significance set at p < 0.05.

3. Results

No pathology was identified in the region of dissection for anyspecimen. A lesser occipital nerve was identified on all sides. Thenerve was not duplicated or triplicated on any side. The lesseroccipital nerve was on average 6.8 cm lateral to the external occip-ital protuberance. However, the nerve was found to have two typesof course. Type I nerves (12 sides; 60%) (Fig. 2) remained close (nogreater than 1 cm) to the posterior border of the sternocleidomas-toid muscle along its entirety, and continued onto the occiput moreor less in line with this posterior border even after the muscleattached to the skull but with a small deviation toward the poste-rior pinna. Some type I nerves crossed anteriorly over the stern-ocleidomastoid muscle near the mastoid process.

Fig. 2. Left-side cadaveric dissection of the lesser occipital nerve. Note that thisrepresents a type I nerve that hugs the posterior border of the sternocleidomastoidmuscle along most of its course and in this case courses laterally and crosses themuscle. The locations of the linear and curvilinear incisions are marked. Note thatthe linear incision transects the nerve while the curvilinear incision cross over thenerve, especially more cranially on the nerve at the apex of the incision.

R.S. Tubbs et al. / Journal of Clinical Neuroscience 32 (2016) 83–87 85

Type II nerves (8 sides; 40%) (Fig. 3) left the posterior border ofthe sternocleidomastoid muscle and swung medially (up to 4.5 cmposterior to the posterior border of the sternocleidomastoid mus-cle) over the nuchal region as they ascended over the occiput.

The lesser occipital nerve was near a midpoint of a line betweenthe external occipital protuberance and mastoid process in allspecimens with a type II nerve configuration. However, type Inerves were found at a point about one third of the distance alonga line drawn from the mastoid process to the external occipitalprotuberance. The linear incision placed the type I nerves at greaterrisk of injury while type II nerves were less likely to be injured viasuch an incision (Fig. 1).

The inverted U incision was less likely to injure the type IInerves but would necessarily cross over type I nerves, especiallymore cranially on the nerve at the apex of the incision. On two(10%) right sides, the lesser occipital nerve pierced the sternoclei-domastoid muscle prior to the muscle’s attachment onto the skull.On one (5%) left side, the nerve pierced the splenius capitis musclebriefly before continuing to the skin overlying the skull. Each ofthese nerves that pierced muscles were type I nerves. Althoughtype II lesser occipital nerves tended to be more frequent on leftsides, this did not reach statistical significance.

Additionally, the traditional linear incision leads to accumula-tion of the scalp and underlying muscle under the retractor thatincreases the working distance of the surgeon toward the cerebel-lopontine angle (CP). The curvilinear incision mobilizes the scalpflap inferiorly and avoids this problem (Fig. 4).

Lastly, traditional linear incisions in this area were more likelyto transect the main trunk of the occipital artery (Fig. 5). The mod-

Fig. 3. Left-sided cadaveric dissection of the lesser occipital nerve. Note that thisrepresents a type II nerve that after emerging from the posterior border of thesternocleidomastoid muscle, the nerve swings away from the muscle and closer tothe midline.

ified U incision was less likely to transect the artery, especiallywhen the medial limb of the incision was shortened. No statisticaldifferences were seen comparing male or female specimens.

4. Discussion

There are relatively few anatomic landmarks that have beencited in the literature for identifying the lesser occipital nerve[5,6]. Most studies have focused on landmarks for the more medi-ally positioned greater occipital nerve [7]. Dash et al. [8] found thatblockage of the lesser occipital nerve was best performed in an areaapproximately 3 cm in diameter centered at a point 6.5 cm fromthe midline and 5.3 cm inferior to a line connecting the externalauditory canals. Another study found that the main lesser occipitalnerve trunk was found on average 7 cm lateral to the externaloccipital protuberance [9]. Our study found that the lesser occipitalnerve has two types and that type I nerves were closer to theregion of the mastoid process in their distribution and weretherefore, more likely to be damaged with the traditionally usedlinear skin incision for retrosigmoid craniotomies. The modifiedU incision, especially when a shorter medial arm was used, wasless likely to transect the main trunk of the lesser occipital nerveand moreover, avoided the main stem of the occipital artery(Fig. 5).

Patients undergoing craniotomy are at risk for chronic head-aches [10–20]. Schankin et al. [21] investigated patients with post-operative headaches following craniotomy and classified the typesof headaches based on criteria defined by the International Head-ache Society [22]. These authors identified five different types ofheadaches and occipital neuralgia was the second most commontype making up 16.6% of postoperative headaches sufferers [21].These postoperative headaches, therefore, might be amenable tosurgical decompression of the nerves overlying the occiput, whichmight be entrapped following craniotomy [23,24]. Moreover, Ducicet al. [1] identified patients with medically recalcitrant postopera-tive headache where the headache resolved following excision ofthe injured cutaneous nerve overlying the occiput. These authorsconcluded that all chronic cases of postoperative headache shouldbe screened for potential occipital nerve injury. In their series, 7patients with postoperative headache had evidence of occipitalnerve injury (neuroma/scar tissue entrapment) and those whounderwent occipital nerve excision were found to have an 80% ormore decrease in headache.

Unrecognized occipital nerve injuries have been found to be aleading cause of chronic occipital neuralgia in patients who haveundergone vestibular schwannoma resection. Treatment of thischronic ipsilateral pain by neuroma excision with implantation ofthe nerve stump to muscle has been described [25]. However,some examples of midline crossing of the occipital nerves havebeen reported so that unilateral injury could result in bilateral pain[5]. Additionally, multiple proximal interconnections between theupper cervical nerves can often result in mixed clinical presenta-tions where the treatment options are not clear [26,27]. Interest-ingly, Schessel et al. [28] modified their incision for cranioplastyin an attempt to avoid occipital nerve injury and found that thishad no effect on the incidence and severity of pain. We have usedthe ‘‘U” incision with a wider base for large posterior fossa tumors,including vestibular schwannomas and have noted rare instancesof patients suffering from chronic headaches.

4.1. The effect of incision on operative distance and working angles

We initially abandoned the linear incision for these retrosig-moid approaches in favor of the ‘‘U” incision due to the difficultieswe encountered while using the linear incision. These difficulties

Fig. 4. (a) The linear incision leads to accumulation of the scalp and underlying muscle under the retractor that increases the working distance of the surgeon toward thecerebellopontine angle, (b) the curvilinear incision mobilizes the scalp flap inferiorly and avoids this problem (with permission from Clarian/IU Health).

Fig. 5. Left-sided occipital artery. The artery is seen emerging into the posteriorneck behind the upper attachment of the sternocleidomastoid muscle and thenswinging medially toward the midline as it ascends.

86 R.S. Tubbs et al. / Journal of Clinical Neuroscience 32 (2016) 83–87

included accumulation of the scalp and underlying muscle underthe retractor that increased the working distance of the surgeontoward the CP (Fig. 4) [29].

Moreover, this increase in the working distance led to limitationof working angles within the CP cisterns. These limitations wereespecially problematic among obese patients. Even though ouroriginal intent was to use the ‘‘U” incision for improving our work-ing distance and angles, we have noticed a decreased rate of post-operative headaches among our patients. However, this conclusionshould be confirmed through a randomized trial.

5. Conclusions

The main trunk of the lesser occipital nerve is near the tradi-tional incisions used for retrosigmoid craniotomy. Based on ourfindings, the inverted U incision, would be less likely to injurethe type II nerves but would necessarily cross over type I nerves,especially more cranially on the nerve at the apex of the incision.As the more traditional linear incision would also most likely tran-sect the type I nerves, the U incision would be the overall betterchoice in avoiding superficial neural injury of the main trunk ofthe lesser occipital nerve and occipital artery during retrosigmoidapproaches. These findings support our recent experience withthe U incision and patients who seem to experience apparently lesspostoperative discomfort and improved wound healing.

Conflicts of Interest/Disclosures

The authors declare that they have no financial or other con-flicts of interest in relation to this research and its publication.

References

[1] Ducic I, Felder JM, Endara M. Postoperative headache following acousticneuroma resection: occipital nerve injuries are associate with a treatableoccipital neuralgia. Headache 2012:1136–45.

[2] Ella B, Langbour N, Caix P, et al. Transverse cervical and great auricular nervedistribution in the mandibular area: a study in human cadavers. Clin Anat2015;28:109–17.

[3] Fukuda H, Evins AI, Burrell JC, et al. A safe and effective technique forharvesting the occipital artery for posterior fossa bypass surgery: a cadavericstudy. World Neurosurg 2014;82:e459–65.

[4] Dandy WE. The brain. MD: WF Prior Company; 1966.[5] Capek S, Tubbs RS, Spinner RJ. Do cutaneous nerves cross the midline? Clin

Anat 2015;28:96–100.

R.S. Tubbs et al. / Journal of Clinical Neuroscience 32 (2016) 83–87 87

[6] Lee M, Brown M, Chepla K, et al. An anatomical study of the lesser occipitalnerve and its potential compression points: implications for surgical treatmentof migraine headaches. Plast Reconstr Surg 2013;132:1551–6.

[7] Cesmebasi A, Muhleman MA, Hulsberg P, et al. Occipital neuralgia: anatomicconsiderations. Clin Anat 2015;28:101–8.

[8] Dash KS, Janis JE, Guyuron B. The lesser and third occipital nerves and migraineheadaches. Plast Reconstr Surg 2005;115:1752–8 [discussion 1759–60].

[9] Tubbs RS, Salter EG, Wellons JC, et al. Landmarks for the identification of thecutaneous nerves of the occiput and nuchal regions. Clin Anat 2007;20:235–8.

[10] Baumann I, Polligkeit J, Blumenstock G, et al. Quality of life after unilateralacoustic neuroma surgery via middle cranial fossa approach. Acta Otolaryngol2005;125:585–91.

[11] Betchen SA, Walsh J, Post KD. Self-assessed quality of life after acousticneuroma surgery. J Neurosurg 2003;99:818–23.

[12] Levo H, Blomstedt G, Hirvonen T, et al. Causes of persistent postoperativeheadache after surgery for vestibular schwannoma. Clin Otolaryngol Allied Sci2001;26:401–6.

[13] Magliulo G, Zardo F, Damico R, et al. Acoustic neuroma: postoperative qualityof life. J Otolaryngol 2000;29:344–7.

[14] Pedrosa CA, Ahern DK, McKenna MJ, et al. Determinants and impact ofheadache after acoustic neuroma surgery. Am J Otol 1994;15:793–7.

[15] Rameh C, Magnan J. Quality of life of patients following stages III–IV vestibularschwannoma surgery using the retrosigmoid and translabyrinthineapproaches. Auris Nasus Larynx 2010;37:546–52.

[16] Rennie C, Haffajee MR, Ebrahim MA. The sinuvertebral nerves at thecraniovertebral junction: a microdissection study. Clin Anat 2013;26:357–66.

[17] Ryzenman JM, Pensak ML, Tew JM. Patient perception of comorbid conditionsafter acoustic neuroma management: survey results from the acousticneuroma association. Laryngoscope 2004;114:814–20.

[18] Ryzenman JM, Pensak ML, Tew JM. Headache: a quality of life analysis in acohort of 1657 patients undergoing acoustic neuroma surgery, results from theacoustic neuroma association. Laryngoscope 2005;115:703–11.

[19] Schwartz MS, Riddle SA, Delashaw JB, et al. Quality of life following acousticneuroma surgery. Neurosurg Focus 1998;5:e3.

[20] Schaller B, Baumann A. Headache after removal of vestibular schwannoma viathe retrosigmoid approach: a long-term follow-up-study. Otolaryngol HeadNeck Surg 2003;128:387–95.

[21] Schankin CJ, Gall C, Straube A. Headache syndromes after acoustic neuromasurgery and their implications for quality of life. Cephalalgia 2009;29:760–71.

[22] Headache Classification Subcommittee of the International Headache Society.The international classification of headache disorders: 2nd edition. Cephalgia2004;24:19–160.

[23] Guyuron B, Reed D, Kriegler JS, et al. A placebo-controlled surgical trial of thetreatment of migraine headaches. Plast Reconstr Surg 2009;124:461–8.

[24] Janis JE, Dhanik A, Howard JH. Validation of the peripheral trigger point theoryof migraine headaches: single surgeon experience using botulinum toxin andsurgical decompression. Plast Reconstr Surg 2011;128:123–31.

[25] Dellon AL, Mackinoon SE. Treatment of the painful neuroma by neuromaresection and muscle implantation. Plast Reconstr Surg 1986;77:427–38.

[26] Lin K, Uzbelger Feldman D, Barbe MF. Transverse cervical nerve: implicationsfor dental anesthesia. Clin Anat 2013;26:688–92.

[27] Shoja MM, Oyesiku NM, Shokouhi G, et al. Anastomoses between lower cranialand upper cervical nerves: a comprehensive review with potential significanceduring skull base and neck operations. Part II: glossopharyngeal, vagus,accessory, and hypoglossal nerves and cervical spinal nerves 1–4. Clin Anat2014;27:131–44.

[28] Schessel DA, Rowed DW, Nedzelski JM, et al. Postoperative pain followingexcision of acoustic neuroma by the suboccipital approach: observations onpossible cause and potential amelioration. Am J Otol 1993;14:491–4.

[29] Kemp WJ, Cohen Gadol AA. A review of skin incisions and scalp flaps for theretromastoid approach and description of an alternative technique. SurgNeurol Int 2011;2:143.

[30] Cohen-Gadol A. The Neurosurgical Atlas. J Neurosurg 2016.