Fascial layers encountered in the lateral skull base region: A cadaveric and radiological analysis

Abstract

Background In our experience, the anterior carotid sheath forms an important plane of dissection when excising temporal bone region cancers. However, its anatomical composition, relationships, and radiological appearance remains unclear. Methods Eight sides of cadaveric heads were dissected. Anatomical findings were correlated with a high‐resolution baseline T1 MRI. Results The anterior carotid sheath was formed by the tensor‐vascular‐styloid fascia, stylopharyngeal fascia, buccopharyngeal fascia (BPF), and longus capitis fascia (LCF), and appeared as a hypointense line on MRI. Not previously described, the glossopharyngeal nerve pierced the sheath 9.0 mm (SD 2.1 mm) below the skull base and traveled through its LCF and BPF layers to exit near the pharynx. Conclusion Multiple fascial layers formed the anterior carotid sheath at the skull base, and this was radiologically identifiable. Further studies are required to validate findings and investigate the role this fascial plane has in forming an effective barrier to spread of malignancy.

Patterns of spread and anatomical prognostic factors of pre‐auricular cutaneous squamous cell carcinoma extending to the temporal bone

“…However, through using the styloid process as a surrogate landmark from which this plane attaches, as demonstrated in our previous anatomical study, some conclusions could still be drawn. 15 We found that only few tumors (n = 6/54, 11.1%) extended medially to erode or encase the styloid, and thus breached the anterior carotid sheath. A larger proportion of patients (n = 20, 37.0%) had tumors that were situated close (≤5 mm) to or abutting the styloid process.…”

“…[10][11][12][13][14] As an initial step, we conducted anatomical cadaveric dissections to further our understanding of the fascial planes in the lateral skull base region. 15 We found a thick fascial plane forming the anterior carotid sheath at the skull base (Figure 1), which could also be identified on high-resolution 3T magnetic resonance imaging (MRI). In our clinical experience, this fascial layer forms a very useful plane of dissection when excising tumors in this region, protecting the major vessels and lower cranial nerves from injury.…”

“…Therefore, for the purposes of analyzing overall patterns of spread and prognostic factors, the styloid process was used as a surrogate marker for this sheath, given their known anatomical relationship, as previously highlighted. 15 We grouped patients as having tumors involving the styloid (encasement or erosion), extending close to the styloid (≤5 mm), or away (>5 mm) from the styloid. Histopathological reports were also reviewed to assess for differences in involved margin rates between these groups.…”

“…F I G U R E 1 The anatomical, radiological, and clinical appearance of the anterior carotid sheath, from Schachtel et al 15 (A) In cadaveric dissections, the anterior carotid sheath was revealed upon removal of the parotid gland, ascending mandible, and pterygoid muscles. (B) Dissection of this thick plane revealed multiple fascial contributions, which together protected the underlying major neurovascular structures.…”