Anatomical assessment of the digastric branch of the facial nerve as a landmark to localize the extratemporal facial nerve trunk

Step-by-Step Dissection of the Extreme Lateral Transodontoid Approach to the Anterior Craniovertebral Junction: Surgical Anatomy and Technical Nuances

BACKGROUND

Multicompartmental lesions of the anterior craniovertebral junction require aggressive management. However, the lesions can be difficult to reach, and the surgical procedure is difficult to understand. The aim of this study was to create a procedural, stepwise microsurgical educational resource for junior trainees to learn the surgical anatomy of the extreme lateral transodontoid approach (ELTOA).

METHODS

Ten formalin-fixed, latex-injected cadaveric heads were dissected under an operative microscope. Dissections were performed under the supervision of a skull base fellowship-trained neurosurgeon who has advanced skull base experience. Key steps of the procedure were documented with a professional camera and a high-definition video system. A relevant clinical case example was reviewed to highlight the principles of the selected approach and its application. The clinical case example also describes a rare complication: a pseudoaneurysm of the vertebral artery.

RESULTS

Key steps of the ELTOA include patient positioning, skin incision, superficial and deep muscle dissection, vertebral artery dissection and transposition, craniotomy, clivus drilling, odontoidectomy, and final extradural and intradural exposure.

CONCLUSIONS

The ELTOA is a challenging approach, but it allows for significant access to the anterior craniovertebral junction, which increases the likelihood of gross total lesion resection. Given the complexity of the approach, substantial training in the dissection laboratory is required to develop the necessary anatomic knowledge and to minimize approach-related morbidity.

Chemodenervation of the Posterior Belly of the Digastric Muscle in Facial Synkinesis

Background: Patients with facial synkinesis may have jaw tightness and swallow discomfort despite chemodenervation of facial mimetic musculature, and the posterior belly of the digastric (PBD) muscle is a logical target to treat these symptoms. Learning/Study Objective: To compare patient-reported outcomes of botulinum toxin (BT) chemodenervation of the posterior belly of digastric muscle in patients with postparalytic facial synkinesis. Design Type: Retrospective review. Methods: Patients with facial synkinesis who underwent electromyography (EMG)-guided PBD BT chemodenervation in addition to their baseline therapeutic regimen were included. Pre- and post-treatment Synkinesis Assessment Questionnaires (SAQ) and a two-question survey regarding jaw tightness and swallow discomfort were administered. Results: Twenty-nine patients were included. An average of 5 U of BT-A was injected into the PBD, and 46.5 U across all facial muscles. From pre- to post-injection, patients demonstrated improvement in jaw tightness at rest (3.02 vs. 1.98/5.0, p < 0.001), with swallow (2.78 vs. 1.94/5.0, p < 0.001), and total SAQ (64.3 vs. 51.2/100, p < 0.001). Patients rated subjective benefit from PBD injection compared with prior treatments without PBD injection as 4.5/5.0. Conclusion: Synkinesis patients with jaw tightness or swallow discomfort may benefit from the addition of PBD injections to the therapeutic regimen.

The Posterior Belly of Digastric Muscle as the Landmark in Facial Nerve Anastomosis Surgery: Anatomical Study and Case Illustration

OBJECTIVE

To establish a new method for fast exposure of the facial nerve and hypoglossal nerve during facial nerve anastomosis surgery.

METHODS

Dissection of 12 formalin-fixed cadaveric specimens was performed to explore the positional relationship between the posterior belly of digastric muscle (PBD) and the facial nerve and hypoglossal nerve. We retrospectively reviewed patients who underwent facial nerve reconstruction surgery between 2015 and 2020 at Xuanwu Hospital, Capital Medical University, and the optimized surgical strategy based on the PBD was proposed.

RESULTS

The trunk of the hypoglossal nerve runs across the external carotid artery after giving off the descendens hypoglossi located within the 1-cm scope deep to the junction of the tendon and belly of the PBD. The mean depth difference between the hypoglossal nerve and the junction of the tendon and belly of the PBD was 5.48 ± 2.24 mm (range, 1.88-9.27 mm). The stylomastoid foramen segment of the facial nerve was revealed after the parotid gland was dissected within the angle between the anterior margin of the mastoid tip and the inferior margin of the cartilage of the external acoustic meatus.

CONCLUSIONS

The facial nerve and hypoglossal nerve can be rapidly identified using the PBD as an anatomical landmark. The end-to-end facial-descendens hypoglossi anastomosis is a reliable facial nerve reconstruction method for patients whose facial nerve was damaged during operation.

Penetration of the facial nerve by the posterior auricular artery: case report, comprehensive review and clinical-surgical applications

Anatomical variations between the facial nerve and adjacent arteries are rare. However, knowledge of such anatomical variations is important to the surgeon who operates on or near the facial nerve. Herein, we report an unusual finding between the extracranial part of the facial nerve and a nearby artery. During routine dissection of the right facial nerve trunk, the posterior auricular artery was found to pierce the nerve effectively forming a nerve loop. The nerve was pierced by the artery soon after its exit from the stylomastoid foramen. This case is detailed and a review on this topic presented, specifically identifying previously reported studies describing this or similar variations, and the relationship between the posterior auricular artery and facial nerve trunk in general. Piercing of the facial nerve trunk by the posterior auricular artery appears to be rare. However, such a relationship should be known by the clinician who treats patients with pathologies of the facial nerve trunk. To our knowledge, this is the first report of this variation in an adult. Due to such rarity, this case is of archival value for those who might describe it or similar cases in the future.

Posterior auricular artery as a novel anatomic landmark for identification of the facial nerve: A clinical study

BACKGROUND

In our previous cadaveric study, we highlighted the posterior auricular artery (PAA) as a potential landmark for early identification of facial nerve (FN) when performing parotidectomy. However, further clinical study is critically needed before this landmark could be applied in clinical practice.

METHODS

For 31 patients enrolled, we tried to identify the FN by the guide of the PAA during parotidectomy. Additionally, the FN function was evaluated during follow-up.

RESULTS

PAA could be exposed in 28 out of 31 (90.3%) patients during parotidectomy. Moreover, the FN trunk could be identified by the guide of the PAA in all these 28 patients with identifiable PAA. Furthermore, no iatrogenic FN damage happened in this study and the transient FN dysfunction rate was 5.7%.

CONCLUSION

The PAA is an ideal landmark for early identification of the FN trunk when performing parotidectomy.

Facial nerve: A review of the anatomical, surgical landmarks and its iatrogenic injuries

Facial nerve iatrogenic injuries are serious and can negatively affect the quality of life of the patients. Due to the properties of the nerve, the complications are devastating involving the aesthetic appearance and the function of the face. Moreover, the multiple branches of the nerve increase the risk of an iatrogenic injury making the detailed knowledge of the anatomical correlations around them critical. In this review, a meticulous analysis was performed including the surgical procedures posing the greater risk of an iatrogenic injury as well as the full description of all the reported anatomical landmarks involving the extracranial course of the facial nerve.

Description and relationships of the parotid gland levels proposed by the European Salivary Gland Society staging system: an anatomical study

OBJECTIVES

To perform an anatomical study to analyze the size, weight, and the relationships of the parotid levels proposed by the European Salivary Gland Society (ESGS).

MATERIALS AND METHODS

Anatomical dissections of the parotid region in 19 human specimens were performed. All dissections were systematically carried out to study the dimensions and weight of each level. We also studied the facial nerve distribution between the different levels and the relative position of the facial nerve main trunk and parotid duct in regard to the Frankfort line plane.

RESULTS

The facial nerve trunk and the parotid duct were identified in all the 19 specimens, which made it feasible to define the 4 principal levels of the parotid gland body (levels I-IV). Level V was identified in 9 out of 19 dissections (47.5%). For the whole gland, the mean for the height and width dimensions were 66.37 mm and 46.84 mm, respectively, and it weighted 18.13 g. In terms of relative weight regarding the whole gland, level II was always the heaviest, representing from 41 to 47% of the gland's weight, depending on the presence of level V. Levels I and III represent almost the same amount of relative weight as they range from 20 to 22% for each one. Level IV was the lightest body level representing 8-10% of the whole, and when present, level V represented less than 5% of the whole parotid weight. The temporal and zygomatic terminal branches were always found between the cranial levels, whereas the cervical and marginal nerves lie in all cases between the caudal levels. The buccal branches had multiple ramifications that lie between both cranial and caudal levels in 47% of the cases, being found exclusively between cranial levels in 21% and between the caudal levels in the remaining 32%.

CONCLUSION

As traditionally reported, the caudal superficial portion of the gland represents the most voluminous portion of the gland, being labeled in our classification as level II. Levels I and III represent similar amounts of gland, though presenting a significantly different morphological disposition. Level IV is the smallest portion of the body gland and level V, when present represents a scarce 5% of the whole body gland weight. The ESGS levels have a clear anatomical basis and the basic references needed to define them are always present.