The Investing Layer of the Deep Cervical Fascia does not Exist between the Sternocleidomastoid and Trapezius Muscles

OBJECTIVE We sought to describe the 3‐dimensional organization of connective tissues in the suboccipital region. STUDY DESIGN AND SETTING We conducted a sectional anatomic investigation with the use of E12 sheet plastination. SUBJECTS Six human adult cadavers (2 male and 4 female; age range, 54 to 86 years) were used in this study. Five of them were sectioned as 2.5‐mm‐thick coronal (1 cadaver), transverse (2 cadavers), or sagittal (2 cadavers) sections. RESULTS No aggregation of fibrous connective tissue was seen between the sternocleidomastoid and trapezius muscles. The intervening space was fully occupied by fatty tissue that was indistinguishable from the subcutaneous tissue. CONCLUSIONS The investing layer of the deep cervical fascia is incomplete so that the carotid sheath is directly exposed to the subcutaneous tissue via a gap between the sternocleidomastoid and trapezius muscle. SIGNIFICANCE This anatomic feature should be considered when designing a minimally invasive endoscopic approach to the carotid sheath and the surrounding deep cervical structures. The eminent success of laparoscopic cholecystectomy has motivated surgeons to expend this minimally invasive surgical approach to the neck–‐for example, the carotid sheath and parathyroid area.1,2 To successfully apply this technique, the knowledge of the detailed configuration of the deep cervical fascia is essential as dissection should be kept in the correct fascial plane to avoid unnecessary damage. On the other hand, deep neck infections are still common despite the wide use of antibiotics,3 and these infections spread along the fascial planes.4 Understanding the fascial planes and deep neck spaces is also essential to managing these infections. Although the anatomy of the deep cervical fasciae is quite complex, its outermost or investing layer is believed to be simple and “everyone is agreed on the existence and disposition of this layer.”5 In brief, the investing layer of the deep cervical fascia is described as a definite continuous sheet of fibrous tissue that completely encircles the neck.6 It attaches posteriorly to the cervical spinal processes7 via the nuchal ligament.5 It envelops 2 muscles, the sternoclaidomastoid and trapezius, and 2 glands, the submandibular and parotid.6,8 However, several recent reports are not consistent with this general description. For instance, a study conducted on serial sections of ten human fetuses has indicated that the superficial surface of the parotid gland is only covered by the subcutaneous tissue.9 It has also been stated that the portion of the investing layer between the sternomastoid and trapezius is areolar connective tissue rather than dense connective tissue.10,11 Using the E12 sheet plastination technique, Johnson et al12 demonstrated that there is no defined nuchal ligament in the upper cervical region, indicating the lack of the direct connection between the investing layer and upper cervical vertebrae. The study of the coniguration of connective tissue in the cadaver is difficult because great difficulties exist in dissecting out the fasciae.6 Under a dissecting microscope, one may be able to trace the aponeurotic or tendon fibres of a muscle, but it is almost impossible to distinguish between the membranous (or fibrous) part of the subcutanous tissue, deep fascia, epimysium, and epitendinium. Although histologic examination may be able to overcome the problem, the application of such method is greatly limited by the size of sample areas. The recently developed E12 sheet plastination technique provides a new approach to illustrate the detailed structural arrangement of the connective tissue at the macroscopic and microscopic levels. Therefore, the aim of this study was to use this technique to describe the 3‐dimensional organization of connective tissues in the suboccipital region.