Sphenomandibularis Muscle and Retro-Orbital Headache
The reasons and sources of temple and retro-orbital headaches have been described in previous articles but they did not include the symptomatic sphenomandibularis muscle—discovered at the University of Maryland by Dunn, Hack, Robbins and Koritzer in 1995 and reported in 1996 in the Journal of Craniomandibular Practice.1 Hormone issues, vascular and migranious causes, muscle tension, muscle contraction, tendonitis, focal myalgia, trauma from falls, blows, tumors, neuralgic and autonomic problems, motor vehicular accidents, TMJ derangements, TMJ migraine, auto-immune issues, and cervical or axial muscle pain referral can all cause headache in the general area of the temple and eye. This list is not exhaustive but simply represents a reasonable partial outline. In the July/August issue of this journal, this author reported of an orbital-inner canthus headache caused by referred pain from the medial or long tendon of the temporal muscle.2 So it is apparent that there are many reasons for eye-related headache, and many of them can be directly or indirectly associated with the structures connected to the temporomandibular joint or as a result of its dysfunction. In this article, the sphenomandibularis muscle and its tendon will be described, along with its potential for acute or persisting retro-orbital and temporal headache.
This important muscle borders 1) the lateral and medial tendons of the temporalis, 2) the mandibular head of origin of the superior pharyngeal constrictor, and 3) the zygomandibularis muscle—all of which have the potential to cause similar pain symptoms from within the mouth. Because of this proximity, it usually requires the anatomical and clinical knowledge and special training of a craniofacial pain dentist (see American Academy of Craniofacial Pain at www.aacfp.com) to confirm the diagnosis. This muscle should be on the physicians’ list of possible causes for headache. All of the structures mentioned above can, and often do, stimulate or refer headache pain near the orbit of the eye. Therefore, a discussion of headache without the inclusion of the dental related structures that so commonly cause or refer headache pain may deny the doctor and patient critical information that would lead to a possible solution for their headache.
This author is very fortunate in having a physician colleague who has a more than passing interest in the dental structures and who refers headache and facial pain patients when he suspects the TMJ or related structures as a possible source of head pain. The reciprocal nature of our professional relationship offers more to our patients than either of us could provide alone.
For example, patients with a spinal accessory nerve deficit, signs of Horner Syndrome, SUNCT Syndrome or NPH, classic migraine, or oral and trigeminal symptoms of pernicious anemia can be initially and provisionally diagnosed in a craniofacial pain dentists’ office then referred to a primary care physician or neurologist for evaluation, testing, and possible treatment. If the physician then suspects the referring craniofacial pain dentist may still be needed, the patient can be referred for re-exam, if necessary.
The sphenomandibularis muscle is considered to be an elevator muscle of the mandible and thus assists the temporalis in closure of the mouth.3 This muscle was found by Dunn et al. while utilizing an atypical anterior-posterior human anatomical dissection technique rather than the traditional lateral approach. The muscle was found to originate from the anterior aspect of the facies temporalis surface (a roughened ridge of bone) of the sphenoid bone behind the orbit (see Figure 1). The typical dimensions of the muscle are one and one-half inches long, three-quarters of an inch wide, and one-quarter inch thick. The muscle inserts at the junction of the ramus and body of the mandible onto the internal oblique line (see Figure 2). Until this anatomical discovery, the internal oblique line of the mandible was only a radiographic landmark and not a reference of clinical value.
A number of other investigators since 1996 have confirmed the muscle discovery, though some assert the muscle is an anomaly or variation of the deep belly of the temporalis muscle but this assertion is thus far unsupported—not to mention that the origins and insertions are different. Woodburne’s 1973 Essentials of Anatomy text expresses the fact that there are many instances of anatomical variation in the muscles: “The same muscle in different individuals may differ as to extend of origin, detail of insertion, or even nerve supply. A muscle may exhibit extra tendons, or it may be entirely missing.”4
Because of the anatomical position of the sphenomandibularis muscle, it is usually destroyed in the dissection process and is thus not available for teaching. However, this muscle is, and can be, identified with MRI scans and by using the Computerized Visible Human Male and Female Data Sets.5
The blood and neural supply to this muscle has not been identified but it is likely derived from the first branchial arch from which are derived the muscles of mastication. Clinical evaluation has associated this muscle with retro-orbital headache. The pain may be localized at the temple or it may also be represented with painful symptoms at the muscle insertion on the internal oblique line of the mandible, intra-orally. The patient may also often point externally to pain in the masseter muscle in the lower cheek area. This location of pain can confuse the diagnosis, as the masseter muscle and the insertion of the stylomandibular ligament and the origin of the mandibular head of the superior pharyngeal constrictor muscle are possible causes or sources of pain at this location. All of these structures converge at, or near, the anatomical junction of the ramus and body of the mandible.