Surface Marking for the Greater Auricular Nerve
The greater auricular nerve emerges at the posterior border of the sternocleidomastoid muscle (SCM) approximately 6.5 cm below the external auditory canal, running parallel to and 0.5 cm posterior to the external jugular vein at this point. 1
Primary Surface Landmarks
Distance-Based Measurements
From the mastoid process: The nerve emerges at the posterior border of the SCM at a mean distance of 6.0 cm (range 5.7-6.9 cm) from the tip of the mastoid process 2, 3
From the external auditory canal: The nerve crosses the posterior border of the SCM 6.5 cm below the caudal edge of the bony external auditory canal 1
Relative to SCM length: The emergence point (great auricular point, GAP) is located at approximately 46% of the total SCM length from the mastoid insertion, with a ratio ranging from 0.33-0.57 3
Relationship to External Jugular Vein
The external jugular vein serves as a critical landmark, running parallel and 0.5 cm ventral (anterior) to the nerve at the point where the nerve crosses the posterior border of the SCM 1
The nerve is located approximately 1.67 cm from the external jugular vein 2
Classification of Nerve Position
The GAP can be classified into two types based on its relationship to the midpoint of the SCM 3:
- Type A (66.7% of cases): GAP is located above the midpoint of the SCM
- Type B (33.3% of cases): GAP is located below the midpoint of the SCM
Anterior Triangle Landmarks
When locating the nerve at the anterior border of the SCM (anterior greater auricular point, AGA) 4:
The nerve crosses the anterior border of the SCM at approximately 29 cm from the mastoid tip and 27.5 cm from the angle of the mandible 4
The nerve crosses an imaginary line drawn between the mastoid tip and angle of the mandible (M-A line) at approximately 48% of the distance from the mastoid tip, always in the middle third of this line 4
Course and Distribution
After emerging at the posterior border of the SCM, the nerve courses superiorly and anteriorly over the surface of the SCM toward the parotid region 2, 5
The nerve typically bifurcates in 55.6% of cases (most commonly in the anterior third of the SCM), trifurcates in 4.4%, and remains undivided in 40% 2
The nerve supplies sensation to the skin over the parotid gland, lower auricle, and mastoid region 2
Clinical Pitfalls to Avoid
McKinney's point (6.5 cm below the external auditory canal at the posterior SCM border) remains the most reliable single landmark for avoiding nerve injury during rhytidectomy and parotidectomy 1
The nerve is most vulnerable where it crosses the midtransverse belly of the SCM, as it is closest to the surface at this location 1
Injury to this nerve results in numbness of the preauricular region, earlobe, and mastoid area, along with potential neuroma formation and pain 5
The nerve has connections with the facial nerve trunk in all specimens and occasionally with the auriculotemporal nerve, making preservation important for maintaining sensory function 5