Posterior Belly Of Digastric Muscle Research Articles

Rare case demonstrating a bifid facial nerve trunk encircling the posterior belly of digastric muscle

This case report describes a variation of facial nerve trunk (FNT) to the digastric muscle identified during parotidectomy where the superior temporofacial branch traverses anterior to the posterior belly of digastric muscle (PBD) and the inferior cervicofacial branch traversing through the muscle. The variation has not been described in literature previously.

Posterior Belly of Digastric Muscle is not Always an Intern's Friend, During Neck Dissection.

Among the various anatomical landmarks during neck dissection, digastric muscle is one of the most important. It is well known that all important blood vessels in neck lies deep to digastric. Thus, it acts as a safety landmark during neck dissection. In this article we describe a variation in vascular anatomy with relation to posterior belly of digastric that has not been reported so far during live surgery. Surgeon performing neck dissection should have a detailed knowledge of anatomy and infrequent anatomical variation. The knowledge of current anatomical variation will avoid torrential bleed during neck dissection and preserve the artery for vascular related procedures.

Usefulness of simultaneous use of anatomical landmarks in identification of facial nerve in parotid gland dissection

Introduction: Identification of Facial nerve trunk is important in parotid surgery to avoid an iatrogenic injury. The objective of our study was to assess consistent and reliable landmarks for identification of the main trunk of facial nerve during parotid surgery.Methods: This prospective study was carried out in the department of Anatomy, faculty of Medicine, Ragama from 2022 to 2023. Our study included 35 fresh cadavers (70 parotid regions). The anatomical landmarks of tragal pointer (TP), tympanomastoid suture (TMS), and superior border of posterior belly of digastric (PBD) muscle to the facial nerve trunk was measured. The shortest distances were taken from the facial trunk by using a slide calliper.Results: The age of subjects of the cadavers ranged from 42 to 64 years with a mean of 54.4 years. The mean distance between the TP and the facial nerve trunk was 9.15 mm (8.1–11.7 mm). The mean distance between PBD and the facial nerve trunk was 8.6 mm (7.2–9.8 mm). The mean distance between the TMS and the facial nerve trunk was 6.5 mm (5.2–7.5 mm).Conclusion: Our study showed that the tympanomastoid suture line is the closest to the facial nerve trunk, followed by the posterior belly of digastric muscle and the tragal pointer respectively. Further clinical studies are needed to assess these landmarks through various parameters to determine their usefulness in surgical practice.

Retromandibular Vein, Digastric Muscle, and Greater Auricular Nerve in Superficial Parotidectomies for Patients with Pleomorphic Adenoma-A Surgical Experience.

Retromandibular vein (RMV) and posterior belly of digastric muscle are among the landmarks used to identify facial nerve in parotid surgery. This observational cross-sectional study was done in the Department of ENT &HNS at a tertiary care teaching hospital for a period of 8 years with the aim to aware young otorhinolaryngologist about the relationship of posterior belly of digastric muscle & retromandibular vein with facial nerve and share our experience about preservation of posterior branch of greater auricular nerve. A total of 34 cases of superficial parotidectomies done for pleomorphic adenoma were included in this study. Relationship of facial nerve with retromandibular vein and posterior belly of digastric muscle was noted. Greater auricular nerve was identified, and every attempt was made to preserve its posterior branch. Retromandibular vein was medial to the trunks of facial nerve in 33 (97%) patients. It was lateral to lower division and medial to upper division in one case. Greater auricular nerve was seen to bifurcate into two branches (Anterior and posterior) in 21 (62%) cases while in one case(3%) three branches were seen emerging from main trunk and in another case(3%) first two branches were seen emerging and then anterior branch was further dividing into two. Preservation of posterior branch of greater auricular nerve was possible in 23 (68%) of patients. Posterior belly of digastric muscle was seen as a reliable and constant landmark. Facial nerve was seen superior to upper border of posterior belly of digastric muscle in all cases (100%). No anatomical variation of posterior belly was seen. Retromandibular vein is invariably seen medial to the trunks of facial nerve. Facial nerve is always seen superior to upper border of posterior belly of digastric muscle in almost all cases. Preservation of posterior branch of greater auricular nerve is possible in majority of the cases.

ROLE OF ANATOMICAL LANDMARKS IN IDENTIFYING FACIAL NERVE DURING PAROTIDECTOMY: OUR EXPERIENCE

Facial nerve paralysis is a common complication during parotid surgery. Various anatomical landmarks are useful for identifying facial nerve location intraoperatively. Our study was conducted in G G Hospital, Jamnagar among 30 patients. Three landmarks which were studied were tragal pointer, tympanomastoid suture, posterior belly of digastric muscle. Tragal pointer was easiest to identify, but mobile, whereas tympanomastoid suture was most consistent in location but difcult to identify. Facial nerve was found to be 1cm above and parallel to upper border of posterior belly of digastric muscle near insertion of mastoid tip.

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

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

Earring Lesion Of The Parotid Tail

Masses in the Parotid tail can be source of consternation to radiologist and clinicians and therefore need attention. Inaccurate localization may lead to significant iatrogenic complications. Anatomically localization lesions of Parotid tails is of relevance as it often creates radiological confusion, as was in this case also. Imaging features of Parotid tail involvement need to be reviewed for, proper understanding and discussed with radiologist for complication free management. A Clinico-radiological correlation reviewing 111 such cases was found which described pleomorphic adenoma(15) , Warthins tumor (14) , infective pathologies, Sjogren disease and also malignant lesions in 27 cases. The notable radiological findings in the cases where enhancement, multiplicity of lesions, on CT and diffusion weighted (varied) signal intensity of MR changes. Relationship of parotid tail/ lesions with surrounding structures like facial nerve or its branches , sternocleidomastoid muscle and posterior belly of digastric muscle, proximity close to the level II LN and posterior part of submandibular salivary gland all need to clearly examined and analyzed. Such a lesion has been referred to as Earring lesions in literature. Earring lesion is best appreciated and less confusing in coronal images and equally challenging in palpation. Though rare, localizing anatomical features of parotid tail lesions are reviewed in this paper along with a case report of parotid tail tumor.

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.

Targeted chemodenervation of the posterior belly of the digastric muscle for the management of jaw discomfort in facial synkinesis

Botulinum toxin (BT-A) chemodenervation has been proved to significantly improve the physical and psychological well-being of patients suffering from facial synkinesis. Despite this, a cohort of patients has persistent tightness and discomfort around the angle of the jaw, which may be caused by synkinesis within the posterior belly of digastric (PBD) muscle. This study was designed to evaluate the benefits of ultrasound-guided BT-A injections into the PBD. Thirty-three patients with recalcitrant tightness and discomfort around the angle of the jaw, despite maximal facial therapy and platysmal chemodenervation were selected for inclusion. Patients underwent ultrasound-guided BT-A injection into the ipsilateral PBD muscle (skin puncture site 1 cm inferior and posterior to the angle of mandible). Outcomes consisted of the Facial Disability Index (FDI), Synkinesis Assessment Questionnaire (SAQ), and a visual analogue scale (VAS) designed to assess tightness and pain around the PBD when moving the jaw, swallowing, and masticating. Questionnaires were completed two weeks before and postinjection. Statistical analysis was performed using a paired t-test. Nineteen patients completed the post-treatment outcome questionnaire. A statistically significant improvement was noted in the physical and social function aspects of the FDI and all aspects of the patient-reported VAS scores apart from tightness and pain on jaw retrusion and swallowing. There was no significant difference in the SAQ. This study has demonstrated the patient-perceived benefit of ultrasound-targeted BT-A chemodenervation of PBD. This represents a low-risk treatment option that can be easily added to the repertoire of treatments offered to patients with post paralysis facial synkinesis.

Anatomical and Surgical Study to Evaluate the Accuracy of "C-M-S" Technique in Facial Nerve Identification During Parotid Surgery.

Facial nerve identification is considered to be a crucial step in parotid surgery as inadvertent injury to the nerve will lead to facial paralysis. Multiple landmarks are described in literature to identify the facial nerve during parotid surgery but controversies remain as the consistency and accuracy of these landmarks vary. Numerous studies exist in literature but they fail to address a single landmark that is most reliable to identify the facial nerve during parotid surgery. The purpose of this study is to find reliable landmarks for identification of the main trunk of facial nerve during parotid surgery by evidence gathered by cadaveric dissection and intraoperative study during parotid surgery and develop a systematic approach to identify the facial nerve trunk. This prospective study included 41 cadavers (82 parotid regions) and 20 patients with parotid pathology who underwent parotidectomy. We evaluated the feasibility of our C-M-S technique to identify the main trunk of facial nerve in both anatomical and surgical study. The relationship of landmarks (tragal pointer, tympanomastoid suture, superior border of posterior belly of digastric muscle) to the facial nerve trunk was assessed and the shortest distance between them from the facial trunk was measured using a slide caliper. The measurements were compared between the anatomical and surgical study. The main trunk of facial nerve was successfully identified in all cases using C-M-S technique in both anatomical and surgical study. Distance of facial nerve trunk to tragal pointer was more in the cadaveric sample (13.04 ± 5.238mm) compared to live patients (9.95 ± 3.967mm) with statistically significant difference (p = 0.036). The mean distance of tympanomastoid suture and posterior belly of digastric muscle to the facial nerve trunk was similar in anatomical and surgical study with p value of 0.877 and 0.083 respectively. The tympanomastoid suture, posterior belly of digastric muscle and tragal pointer are the most useful landmarks for facial nerve identification during parotid surgery. In our study we found that the tympanomastoid suture line is the most consistent landmark present in all our cases and being closest to the facial nerve trunk in both anatomical and surgical study. Further we recommend using the "C-M-S technique" in order to locate the main trunk of the facial nerve.

Do Benign Mass Lesions in the Superficial Lobe of Parotid Gland Influence Landmark-Based Search for Facial Nerve Trunk at Surgery?

ObjectiveTo assess the influence of benign mass lesions in the superficial lobe of parotid on the known anatomic landmarks for identifying the facial nerve trunk.MethodPatients with unilateral biopsy-proven benign mass lesions in the superficial parotid were selected for this observational study. During superficial/partial superficial parotidectomy, distance of the facial nerve trunk from each landmark was assessed using spring calliper and correlated with the lesion’s volume (measured from the pre-operative imaging). At least two identifiers among tragal pointer (TP), posterior belly of digastric muscle (PBDM) and tympanomastoid suture (TMS) were considered.ResultsThe study involved 32 patients. The lesions mostly involved the parotid tail (50%) and pretragal region (34.3%), and constituted of pleomorphic adenoma (~66%) and Warthin’s tumor (~9%), the rest being various cysts and hamartomas. TP was universally uncovered, while PBDM and TMS were exposed in 26 and 25 patients, respectively. Average distances between the facial nerve trunk and TP, PBDM and TMS were 12.79 mm (SD=2.33), 9.78 mm (SD=1.21) and 7.58 mm (SD=1.33), respectively. Correlation coefficients between the lesion’s volume and the distance of facial nerve from a given landmark were -0.11, 0.04 and -0.16 for TP, PBDM and TMS, respectively.ConclusionTP was the most easily available landmark on surgical dissection, while PBDM was the most consistent and the least variable when volumetric data of the benign mass lesions in the superficial lobe of parotid were considered as a factor influencing the distance from the facial nerve trunk.

Posterior Belly of Digastric Muscle Transposition Flap in Preventing Frey's Syndrome after Superficial Parotidectomy- A Prospective Study.

Introduction:Superficial parotidectomy is an effective management for benign and malignant tumours of the superficial lobe of the parotid gland. Frey's syndrome is one of the most common complications observed after parotidectomy. The objective of our study was to find the incidence of Frey's syndrome 6 months and 1 year postoperatively after doing posterior belly of the digastric flap during superficial parotidectomy.Materials and Methods:This is an observational prospective study done in the Department of General Surgery of the Institute from November 2018 to December 2020. Thirty-eight patients with parotid swellings (both due to benign or malignant causes) were evaluated preoperatively and planned for superficial parotidectomy with a posterior belly of digastric muscle (PBDM) flap to prevent the occurrence of Frey's syndrome. They were followed up in 6 months and 1 year. Minor's test was done in each visit to look for the occurrence of Frey's syndrome.Results:Two patients (5.2%) out of 38 patients developed asymptomatic Frey's syndrome after 6 months postoperatively out of which one patient (2.6%) developed symptomatic Frey's syndrome after 9 months postoperatively with symptoms such as sweating, flushing, and redness over the parotid area during chewing.Discussion:PBDM flap following superficial parotidectomy in a single-stage surgery is an effective and easy method to prevent Frey's syndrome. This procedure is easy to perform and requires no complex dissection. There have not been many studies regarding the use of this flap; hence, this study may be considered as a pilot study.

POSTERIOR BELLY OF DI-GASTRIC MUSCLE – THE LANDMARK TO IDENTIFY FACIAL NERVE IN PAROTIDECTOMY

Objective:-To document Posterior belly of Di-gastric Muscle – The landmark to identify Facial Nerve in Parotidectomy. Methods:- In this study, relationship between posterior belly of digastrics and facial nerve trunk recorded in 21 patients who undergone Parotidectomy in our Institute. Results:-In all patients, Facial Nerve trunk was identified above the posterior belly of Di-gastric muscle with range of 5 to 10 mm. Conclusion:-This study confirmed that posterior belly of Di-gastric muscle in the landmark in identification of Facial nerve trunk in Parotidectomy.

Surgical Pitfalls in Carotid Endarterectomy: A New Step-By-Step Approach.

Carotid endarterectomy (CEA) is a surgical intervention that may prevent stroke in asymptomatic and symptomatic patients. Our aim was to examine the microsurgical anatomy of carotid artery and other related neurovascular structures to summarize the CEA that is currently applied in ideal conditions. The upper necks of 2 adult cadavers (4 sides) were dissected using ×3 to ×40 magnification. The common carotid artery, external carotid artery (ECA), and internal carotid artery were exposed and examined. The surgical steps of CEA were described using 3-D cadaveric photos and computed tomography angiographic pictures obtained with help of OsiriX imaging software program. Segregating certain neurovascular and muscular structures in the course of CEA significantly increased the exposure. The division of facial vein allowed for internal jugular vein to be mobilized more laterally and dividing the posterior belly of digastric muscle resulted in an additional dorsal exposure of almost 2 cm. Isolating the ansa cervicalis that pulls hypoglossal nerve inferiorly allowed hypoglossal nerve to be released safely medially. The locations of the ECA branches alter depending on their anatomical variations. The hypoglossal nerve, glossopharyngeal nerve, and accessory nerve pierce the fascia of the upper part of the carotid sheath and they are vulnerable to injury because of their distinct courses along the surgical route. Surgical exposure in CEA requires meticulous dissection and detailed knowledge of microsurgical anatomy of the neck region to avoid neurovascular injuries and to determine the necessary surgical maneuvers in cases with neurovascular variations.

Optimization of cervical lymph node clinical target volume delineation in nasopharyngeal carcinoma: a single center experience and recommendation.

Nasopharyngeal carcinoma (NPC) are characterized by distinct lymph node metastasis patterns. In order to minimize cervical lymph node irradiation volume, 379 NPC patients with metastatic cervical lymph nodes were eligible for geographic mapping. All lymph nodes were mapped into simulation computed tomography images of a template lymph node negative patient. The proportions of retropharyngeal lymph nodes (RLNs), Level Ib, II, III, IV, Va, Vb and supraclavicular (SCV) lymph nodes were 6.9%, 0.5%, 55.25%, 20.4%, 8.2%, 4.9%, 3.1% and 0.75%, respectively. Based on their distribution profile, we proposed the following modifications: 1. the lateral border of RLNs clinical target volume (CTV) be the medial edge of the internal carotid artery above the level of mastoid process, the medial border be adjacent to the cervical vessels below the free edge of the soft palate; 2. the submandibular gland should not be included in Level Ib; 3. Level II should include the posterior belly of digastric muscle, and the space between the posterior edge of submandibular gland and the anterior edge of sternocleidomastoid muscle; 4. the anterior border of Level III and IV should gradually shift backwards and the CTV only include part of the cervical vessels below the level where the thyroid gland appears; 5. the space of the posterior edge of trapezius muscle also should be included if there are metastatic lymph nodes in the transverse cervical vessle plexus. Our recommendations might adequately encompass metastatic lymph nodes while sparing the organs at risk and reducing adverse events.

Post Parotidectomy Quality of Life in Patients with Benign Parotid Neoplasm: A Prospective Study

Parotid tumours are not uncommon. The management is surgical for benign and malignant parotid neoplasm. Due to the location of parotid gland and its intricate relationship with facial nerve, cosmetic and functional outcomes after parotid surgery are extremely important. Objectives of the study were to analyse facial nerve functions with emphasis on the quality of life of patients undergoing surgery for parotid neoplasm. A prospective study was conducted on patients presented with parotid neoplasm and undergone parotid surgery. Patient with malignant neoplasm were excluded. 30 patients with benign parotid neoplasm in final histopathology were included in the study. Post operative assessment of facial nerve was done using postparotidectomy facial nerve grading system. Symptom-specific QOL was assessed with the parotidectomy outcome inventory-8. Aesthetic outcome was evaluated with an ordinal scale. Posterior belly of digastric muscle and tragal pointer were the commonest landmark used for facial nerve identification. Temporary facial nerve dysfunction was present in six (20%) patients with marginal mandibular branch most commonly involved. 96% of the female patients and 91% of the male patients rated the cosmetic result as good or very good. A statistically significant difference is noted between superficial parotidectomy and total Parotidectomy for cosmetic outcome and sensory impairment. We noted that changed appearance due to resection of the parotid gland and scar and sensory impairment in the area affect the quality of life of patients and such affect are more after total conservative parotidectomy.

Surgical anatomy of hypoglossal nerve as a guide for important head and neck surgeries

IntroductionThe hypoglossal nerve (HN) may be damaged during neck surgeries. A detailed understanding of the anatomy of the hypoglossal nerve in relation to various anatomical landmarks and surrounding structures is important to reduce procedural complications and the risk of nerve damage. MethodsThe study was carried out using 21 sagittal sections of head and neck of male cadavers (16 right and 5 left). To measure the required parameters the anatomical landmarks taken were the posterior belly of digastric muscle (PBD), descendens hypoglossi of ansa cervicalis (AC), bifurcation of common carotid artery (CCA), tip of the mastoid process (TMP), lingual artery (LA) at the posterior border of hyoglossus muscle, tip of greater cornu of hyoid bone (GH), bifurcation of CCA to the attachment of descendens hypoglossi (CCA-AC). ResultsThe length of PBD was 3.77±1.08cm on right side and 3.15±0.05cm on left side. The extended length was measured from the TMP to GH which was 6.7±1.23cm on right side and 6.75±0.75 on left side. The distance between HN to the GH did not vary much between right and left sides which were 1.21±0.35 and 1.2±0.69cm respectively. The distance between HN and LA at the posterior border of hyoglossus was 1.12±0.3cm on right side and 0.5±0.3cm on left side. DiscussionHN dissection is more complicated, as the location of the HN is much deeper. Moreover, there are no bony landmarks around the HN. Therefore PBD, CCA, ICA, ECA, LA were used as landmarks for HN in head and neck surgeries.

Craniovertebral junction 360°: A combined microscopic and endoscopic anatomical study.

Objectives:Craniovertebral junction (CVJ) can be approached from various corridors depending on the location and extent of disease. A three-dimensional understanding of anatomy of CVJ is paramount for safe surgery in this region. Aim of this cadaveric study is to elucidate combined microscopic and endoscopic anatomy of critical neurovascular structures in this area in relation to bony and muscular landmarks.Materials and Methods:Eight fresh-frozen cadaveric heads injected with color silicon were used for this study. A stepwise dissection was done from anterior, posterior, and lateral sides with reference to bony and muscular landmarks. Anterior approach was done endonasal endoscopically. Posterior and lateral approaches were done with a microscope. In two specimens, both anterior and posterior approaches were done to delineate the course of vertebral artery and lower cranial nerves from ventral and dorsal aspects.Results:CVJ can be accessed through three corridors, namely, anterior, posterior, and lateral. Access to clivus, foreman magnum, occipital cervical joint, odontoid, and atlantoaxial joint was studied anteriorly with an endoscope. Superior and inferior clival lines, supracondylar groove, hypoglossal canal, arch of atlas and body of axis, and occipitocervical joint act as useful bony landmarks whereas longus capitis and rectus capitis anterior are related muscles to this approach. In posterior approach, spinous process of axis, arch of atlas, C2 ganglion, and transverse process of atlas and axis are bony landmarks. Rectus capitis posterior major, superior oblique, inferior oblique, and rectus capitis lateralis (RCLa) are muscles related to this approach. Occipital condyles, transverse process of atlas, and jugular tubercle are main bony landmarks in lateral corridor whereas RCLa and posterior belly of digastric muscle are the main muscular landmarks.Conclusion:With advances in endoscopic and microscopic techniques, access to lesions and bony anomalies around CVJ is becoming easier and straightforward. A combination of microscopic and endoscopic techniques is more useful to understand this anatomy and may aid in the development of future combined approaches.

Facial nerve trunk variations with surgical implications: A cadaveric study

Purpose: Anterograde identification of facial nerve trunk (FNT) identification is paramount, because FNT injury causes substantial morbidity. This study reexamines controversial landmarks and considers the importance of gender and dentition in landmark choice. MethodsDistances from key landmarks to FNT were measured and compared by side, gender and dentition (92 specimens). Landmarks included posterior belly of digastric muscle (PBM), tragal pointer (TP), mastoid process (MP), external acoustic meatus (EAM) and transverse process of axis (TPA). ResultsTwo-sample T tests showing longer distances from: MP/TPA to FNT in men than in women (14.8 ± 2.2 mm vs. 13.5 ± 1.6 mm, P = 0.004; 37.6 ± 4.4 mm vs. 32.7 ± 4.2 mm, P = 0.001); EAM to FNT on occlusal sides than on the counterparts (14.2 ± 1.8 mm vs. 16.0 ± 3.8 mm, P = 0.020). One-sample T tests showing longer distances from: TP to FNT on right than on left side (21.4 ± 2.7 vs. 19.9 ± 2.9, P = 0.006); MP to FNT on the less dentulous maxillae than on the counterpart (14.4 ± 2.1 vs. 13.0 ± 1.6, P = 0.027); PBM/EAM to FNT on the less dentulous mandible than on the counterpart (9.8 ± 1.6 vs. 7.8 ± 2.5, P = 0.039; 16.4 ± 3.0 vs. 14.1 ± 1.5, P = 0.020). ConclusionSurgeons should be aware that distances of MP, PBM and EAM, to FNT, are lengthened in less dentulous patients, especially when maxilla and mandibles are non-occlusive. Overall, soft landmarks are less reliable than osseous landmarks.

Detailed knowledge of regional anatomy and anatomical variations is fundamental to achieve successful surgical procedure. Although primary objective of neurosurgery is to restore physiological vital functions, remove intracranial mass and prevent further

Detailed knowledge of regional anatomy and anatomical variations is fundamental to achieve successful surgical procedure. Although primary objective of neurosurgery is to restore physiological vital functions, remove intracranial mass and prevent further brain damage, while preserving tissue and organ integrity, the neurosurgeon takes the risk of impairing non-vital functions. Occasionally, as with the hypoglossal nerve, the impairment of anatomical structures found on surgical route is due to their still barely known anatomical relations and variations. In order to provide an anatomically and surgically oriented classification to guide neurosurgical procedures and to ensure the preservation of nerve integrity, the aim of the present study is to detail the course of the 12th cranial nerve (CN) and to establish anatomical landmarks for surgeons. A combination of anatomical dissection of the neck and oral floor and skull base far lateral approach of 6 cadaveric human heads (3 male, 3 female, age 62+4) was performed, on both sides, to explore and follow the entire course of the 12th CN, from its emergence in the preolivary sulcus to the tongue. Skeletal, muscular and vascular relationships were meticulously analyzed and documented during anatomic and surgical dissections. According to our observations, hypoglossal nerve can be divided into five segments. The first two are intracranial, cisternal and intracanalar, and the other three, namely the descending, horizontal and ascending, are extracranial. Intriguingly, we found unreported relations of the nerve that, apart from their anatomical interest, have tremendous significance for surgeons operating on head and neck. Specifically, the intracanalar segment passes through a venous lacuna that, to the best of our knowledge, was never described before as such. This venous structure drains into the jugular bulb and acts as a sheath between the nerve and the osseous wall of the canal. The nerve in the venous sheath bends and it is elastically fixed to the osseous wall of the canal by fibrous bands. Therefore, the venous lacuna guarantees mobility to the nerve, and cushion the nerve from the bone. As for the descending segment, during its course it has very close relationship with the internal jugular vein, the internal carotid artery, the posterior belly of digastric muscle, and the styloid process and muscles inserting on it. The descending segment provides the ansa hypoglossi, branches to muscles inserting on the styloid process and to the sternocleidomastoid muscle. The horizontal segment has relationship with the intermediate digastric tendon, the stylohyoid, hyoglossus and mylohyoid muscles and the submandibular gland. The ascending segment might be very short and sometimes it is absent. The fifth and last segment becomes deeper at the anterior edge of hyoglossus muscle, and terminates into several branches supplying intrinsic and extrinsic musculature of tongue.