Single Incision Approach for Decompression of Greater, Lesser and Third Occipital Nerves in Migraine Surgery

The traditional approach for occipital migraine surgery encompasses 3 separate surgical incisions in the posterior neck to decompress the great occipital nerves (GON), lesser occipital nerves (LON) and third occipital nerves (TON). We sought to evaluate a single incision approach for decompression of all


Results
The GON and TON were identi ed 3.5 and 6.2 cm, respectively inferior to a line bisecting the external auditory canal (EAC) and 1.5 cm lateral to the midline. The LON was identi ed 6-cm inferior and 6.5-cm medial to a line bisecting the EAC in the plane just above the investing layer of the deep cervical fascia until the posterior boarder of the sternocleidomastoid was encountered. The LON had the greatest amount of variation, but was identi ed lateral to the posterior border of the SCM.

Conclusions
A single midline incision approach allows for successful identi cation and decompression of all 6 occipital nerves in migraine surgery.

Background
Migraine headaches ranked as the third most prevalent disorder in the world in 2010 and the third-highest cause of disability worldwide in both males and females under the age of 50 years in 2015. 2 The pain of occipital migraines is located in the upper neck and occipital region is associated with stress, muscle tightness, trigger point tenderness, and may be related to heavy exercise or history of whiplash. [10][11] Advances in the underlying pathophysiology have led to promising treatment modalities, such as botulinum toxin A (BTX-A) injections and migraine surgery. [7][8] Traditional release of these nerves involved in occipital migraines requires 3 separate incisions in the posterior neck.
Anatomic studies have de ned the location of each of the nerves associated with occipital migraine headaches. These include the bilateral great occipital nerves (GON), bilateral lesser occipital nerves (LON) and bilateral third occipital nerves (TON). 12 The location of these nerves and their emergence from under muscle and fascia is key for successful treatment with BTX-A injections or surgical treatment. (Table 1) In a systematic review, migraine headache surgery reported an average success rate of 90% with either elimination or 50% or greater improvement of migraine headaches. 9 Sixty-two percent of patients with occipital migraine headaches reported total relief of migraine symptoms and all patients had some element of improvement in migraine headaches after open release of GON. 8 Table 1 Location of previously de ned sites of great occipital (GON), lesser occipital (LON) and third occipital nerves (TON).
Distance from midline Distance from line between auditory canals The TONs were marked 1.3-cm from midline and 6.2-cm from the EAC. 12 We then designed a 9-cm long midline incision in the caudal occipital region down into the superior neck (Fig. 1).
The incision was made through the skin and subcutaneous tissue down to the midline raphe. Large subcutaneous skin aps were raised laterally just above the investing layer of the deep cervical fascia.
When the posterior board of the SCM was encountered, dissection was continued with spreading technique to identify the LON along the posterior boarder of the SCM. Once the LON was identi ed, it was followed superiorly to con rm its identity and avulsed or sites of compression were released until the nerve entered the subcutaneous tissue.
The GON and TON were routinely addressed after the LON to avoid confusing the planes. The trapezius fascia was incised 0.5-cm lateral to midline leaving the midline raphe intact. When present, the oblique trapezius muscle was retracted laterally. The semispinalis capitus was found just below the fascia running in the vertical direction and dissection was carried subfascial until trunk of GON was identi ed. 2.5-cm of the semispinalis muscles medial to nerve was excised. Each compression point was released as the nerve was followed distally to its entrance to the subcutaneous tissue. During the release of the GON, the TON was encountered a similar distance from midline but inferior to the GON. It was avulsed as its sensation contributions are small. (Fig. 2 and Fig. 3)

Results
Ten cadaveric hemi-sides were dissected. Each of the nerves were sequentially identi ed. The GON and TON were consistently located at their anatomic landmarks. The LON had more variation in its location and could be challenging to identify in some instances. The most common dissecting error encountered was being in a deeper plane than the SCM. The posterior border of the SCM lies super cial to the subcutaneous tissues of the neck and the LON is easiest to identify emerging posterior to the SCM muscle and coursing upwards towards the occiput. The great auricular nerve (GAN) emerges superior to the LON and courses more anterior. The GAN can be mistaken for the LON, as they both emerge posterior to the SCM. Tracing the nerve to its nal location avoids inadvertent injury to an unintended structure, like the GAN.
The LON varies in its caliber from 1-4 mm in size and at its emergence from the SCM can course near the spinal accessory nerve (SAN). The SAN runs obliquely and inferior to the LON, but their emergence around the SCM can be at a similar location. Following the LON to the posterior occiput can con rm its identity. A nerve stimulator can also help con rm if motor bers are present.
After each nerve was dissected and photos were taken, the skin aps were retracted to follow the course of the nerves to further con rm their identities. The LON was challenging to locate in 2 (4 hemi-sides) of the cadaver heads requiring more extensive and prolonged dissection. Keeping the dissection plan super cial to the SCM helped maintain landmarks and ease the identi cation of the nerves. The dissection plane created from the midline only requires skin ap elevation of 3-4 additional centimeters on each side and can provide a broader perspective on the location of each nerve.

Discussion
Traditionally occipital migraine surgery is performed with 3 separate incisions to decompress the GON, TON and LON. More incisions can increase pain, neuroma formation and risk of wound breakdown. Scars on the back tend to widen and many patients are female with concern for aesthetic appearance of the scars. We have successfully performed a single incision release of all 6 nerves in 6 hemi-necks. The consistent and well-de ned anatomic location of the GON, LON and TON makes this single incision approach safe and feasible.
During the dissection it is essential to create large skin aps to achieve adequate exposure. The skin aps should be elevated just above fascia to preserve the musculature and fascial planes. The fascia should be entered just at the posterior boarder of the SCM to locate the LON. It is also important to note the course of the LON as it emerges from the posterior aspect of the SCM and then travels on the anterior surface of the SCM. The great auricular nerve emerges just inferior and follows a similar course. 16 The TON is in close in proximately to the GON located just inferior as it pierces the semispinalis muscle but is smaller in caliber and can be easily missed.
After completing this study, we now perform this technique in occipital migraine surgery. In the preoperative area, we mark the posterior boarder of the SCM with the patient turning head laterally against resistance in the pre-operative area and the precise location of the LON can be identi ed as the examiner rolls his ngers over the posterior border of the SCM, the location of pain signi es the location of the LON.
Decompression of nerves is performed by technique described above. 1 drain is placed under the subcutaneous aps and secured in place to minimize uid accumulation and dead space. The incision is closed in a layered fashion.

Conclusions
Occipital migraine surgery has been established as a bene cial treatment option, but traditionally requires 3 separate incisions to release the paired GON, LON and TON. These six nerves can all be accessed and released through a single midline incision. The course of the LON has the most variation and be the most challenging to locate, however, the wider midline approach can provide anatomic perspective for successful identi cation of each of the nerves, while preserving the planes and musculature in the posterior neck. A. Marked anatomic location of GON 1.5-cm from the midline and 3.5-cm from the EAC (red), LON 6.5-cm from midline and 6-cm from the EAC (blue), TON 1.3-cm from midline and 6.2-cm from the EAC (green) B. Marked 8-cm midline incision in the caudal occipital region down into the superior neck. Lateral skin ap raised just above the investing layer of the deep cervical fascia with exposed GON (red arrow), LON (blue arrow), TON (green arrow).