Microsurgical anatomy of the hypoglossal nerve

Hypoglossal nerve delineation in nasopharyngeal carcinoma patients may reduce the radiation dose and damage to the nerve

This study aims to establish a delineation guideline for the contouring of the hypoglossal nerve by dividing the nerve into different segments, and to test the possibility of a radiation dose reduction to the hypoglossal nerve in NPC patients receiving radiotherapy. Twenty NPC patients were selected arbitrarily. The hypoglossal nerves were delineated using anatomic landmarks and divided into the cisternal, intracanalicular, carotid, and transverse segments. The tumor coverage by radiation and dose-volume parameters of the nerve with and without various dose constraints to the hypoglossal nerve were compared. The hypoglossal nerve, which is invisible on CT images, can be delineated accurately with the assistance of several anatomic landmarks. Without a dose constraint to the hypoglossal nerve, the carotid space, intracanalicular, and transverse segments had high radiation dose-volumes. The dose-volume to the nerve, however, can be reduced when the nerve was defined and a dose constraint was given. The delineation of the hypoglossal nerve with its different segments is feasible. The carotid space, intracanalicular, and transverse segments received the highest dose, where the nerve damage was most likely located. The dose to the nerve can be reduced to less than 70 Gy using the intensity-modulated radiotherapy technique.

Cadaver investigation of the usefulness of the transstyloid diaphragm approach for high-position plaque carotid endarterectomy

OBJECTIVES

Patients sometimes present with high cervical internal carotid artery (ICA) stenosis. This study demonstrates the usefulness of the transstyloid approach to expose the distal ICA by dissection of the styloid diaphragm covering the distal cervical ICA for carotid endarterectomy (CEA). In particular, the possible exposure length achieved by this approach was investigated using cadaveric heads.

METHODS

The procedure of the transstyloid diaphragm approach was confirmed in 10 cadaveric heads (20 sides). After the carotid triangle was opened, both the posterior belly of the digastric muscle (PBDM) and the stylohyoid muscle could be divided. Then, the carotid sheath was dissected, and the glossopharyngeal nerve was identified crossing over the distal ICA. The revealed length of the ICA was measured with or without dissection of both the PBDM and the stylohyoid muscle. The specimens were dissected under the surgical microscope.

RESULTS

The transstyloid diaphragm approach was achieved successfully in all specimens. The revealed lengths of the ICA with and without dissection of the styloid diaphragm were 53.7 ± 5.9 mm and 38.8 ± 2.9 mm (mean ± standard deviation), respectively. Therefore, the revealed length of the distal ICA was 14.9 ± 4.5 mm greater using the transstyloid diaphragm approach compared to the regular CEA approach.

CONCLUSIONS

More of the ICA can be revealed by dissection of both the PBDM and the stylohyoid muscle. The transstyloid diaphragm approach might be helpful to reveal the distal ICA in cases of high cervical ICA stenosis.

The ptotic tongue-imaging appearance and pathology localization along the course of the hypoglossal nerve

CT and MRI findings of tongue ptosis and atrophy should alert radiologists to potential pathology along the course of the hypoglossal nerve (cranial nerve XII), a purely motor cranial nerve which supplies the intrinsic and extrinsic muscles of the tongue. While relatively specific for hypoglossal nerve pathology, these findings do not accurately localize the site or cause of denervation. A detailed understanding of the anatomic extent of the nerve, which crosses multiple anatomic spaces, is essential to identify possible underlying pathology, which ranges from benign postoperative changes to life-threatening medical emergencies. This review will describe key imaging findings of tongue denervation, segmental anatomy of the hypoglossal nerve, imaging optimization, and comprehensive imaging examples of diverse pathology which may affect the hypoglossal nerve. Armed with this knowledge, radiologists will increase their sensitivity for detection of pathology and provide clinically relevant differential diagnoses when faced with findings of tongue ptosis and denervation.

Duplication of the Hypoglossal Nerve Branch to the Thyrohyoid Muscle: A Case Report

The motor fibers to the thyrohyoid muscle are provided by the anterior ramus of C1 via the hypoglossal nerve rather than via the ansa cervicalis. Knowledge of possible variations in the branching patterns of the nerves attached to the hypoglossal nerve is necessary to minimize iatrogenic injury to these structures during surgical procedures. We describe a rare anatomical variant of the nerve branch to the thyrohyoid muscle. To our knowledge, this particular variant has not been previously reported.

Atavistic and vestigial anatomical structures in the head, neck, and spine: an overview

Organisms may retain nonfunctional anatomical features as a consequence of evolutionary natural selection. Resultant atavistic and vestigial anatomical structures have long been a source of perplexity. Atavism is when an ancestral trait reappears after loss through an evolutionary change in previous generations, whereas vestigial structures are remnants that are largely or entirely functionless relative to their original roles. While physicians are cognizant of their existence, atavistic and vestigial structures are rarely emphasized in anatomical curricula and can, therefore, be puzzling when discovered incidentally. In addition, the literature is replete with examples of the terms atavistic and vestigial being used interchangeably without careful distinction between them. We provide an overview of important atavistic and vestigial structures in the head, neck, and spine that can serve as a reference for anatomists and clinical neuroscientists. We review the literature on atavistic and vestigial anatomical structures of the head, neck, and spine that may be encountered in clinical practice. We define atavistic and vestigial structures and employ these definitions consistently when classifying anatomical structures. Pertinent anatomical structures are numerous and include human tails, plica semilunaris, the vomeronasal organ, levator claviculae, and external ear muscles, to name a few. Atavistic and vestigial structures are found throughout the head, neck, and spine. Some, such as human tails and branchial cysts may be clinically symptomatic. Literature reports indicate that their prevalence varies across populations. Knowledge of atavistic and vestigial anatomical structures can inform diagnoses, prevent misrecognition of variation for pathology, and guide clinical interventions.

The Hypoglossal nerve

The hypoglossal nerve is the 12th cranial nerve, exiting the brainstem in the preolivary sulcus, passing through the premedullary cistern, and exiting the skull through the hypoglossal canal. This is a purely motor nerve, responsible for the innervation of all the intrinsic tongue muscles (superior longitudinal muscle, inferior longitudinal muscle, transverse muscle, and vertical muscle), 3 extrinsic tongue muscles (styloglossus, hyoglossus, and genioglossus), and the geniohyoid muscle. Magnetic resonance imaging (MRI) is the best imaging exam to evaluate patients with clinical signs of hypoglossal nerve palsy, and computed tomography may have a complementary role in the evaluation of bone lesions affecting the hypoglossal canal. A heavily T2-weighted sequence, such as fast imaging employing steady-state acquisition (FIESTA) or constructive interference steady state (CISS) is important to evaluate this nerve on MRI. There are multiple causes of hypoglossal nerve palsy, being neoplasia the most common cause, but vascular lesions, inflammatory diseases, infections, and trauma can also affect this nerve. The purpose of this article is to review the hypoglossal nerve anatomy, discuss the best imaging techniques to evaluate this nerve and demonstrate the imaging aspect of the main diseases that affect it.

The Glossopharyngeal, Vagus and Accessory nerves: Anatomy and Pathology

The glossopharyngeal, vagus, and accessory nerves are discussed in this article, given their intimate anatomical and functional associations. Abnormalities of these lower cranial nerves may be intrinsic or extrinsic due to various disease processes. This article aims to review these nerves' anatomy and demonstrates the imaging aspect of the diseases which most commonly affect them.

Stereotactic radiosurgery for the treatment of hypoglossal schwannoma: a multi-institutional retrospective study

BACKGROUND

Surgical removal has been performed as the first line treatment for symptomatic or enlarging hypoglossal schwannomas (HS). Stereotactic radiosurgery (SRS) offers a minimally invasive approach that may afford long-term tumor control for patients with HS particularly those who refuse or are unfit for surgery. This study evaluates outcomes after SRS performed for both newly diagnosed and residual tumors after incomplete resection.

METHODS

This retrospective, multi-institutional study involved patients treated with adjuvant or primary SRS for HS. The study end-points included local tumor response, clinical outcomes, and procedure-related complications. All the patients had Gamma Knife SRS.

RESULTS

The cohort included 12 patients (five females), median age at SRS 49.5 years (range, 37-76)]. The median tumor target volume was 5.9 cm³ (range, 0.7-27.23). At median imaging follow-up of 37 months (range, 6-153), tumor control was achieved in 11 patients. Tumor enlargement that was managed with surgical resection was noted at the 6-month follow-up in one patient. At median clinical follow-up of 30.5 months (range, 6-157), stability, or improvement of all pre-SRS signs and symptoms was noted in nine patients. Two patients experienced worsening of at least one pre-existing symptoms or sign. New-onset trapezius weakness was noted in one patient and tongue atrophy in two patients.

CONCLUSION

Single-fraction SRS appears to be a safe and effective upfront and adjuvant treatment option for HS. SRS may be recommended as an alternative to surgery for patients presenting with HS or as an adjuvant treatment following subtotal resection and at HS recurrence.

Godtfredsen syndrome - recurrent clival chondrosarcoma with 6 years follow up: a case report and literature review

BACKGROUND

We report a rare case of Godtfredsen syndrome caused by clival chondrosarcoma and perform a review of literatures. This article also explains the clinico-anatomical correlation of this rare neurological syndrome.

CASE PRESENTATION

A 22-year-old gentleman presented with binocular diplopia. Clinical examination revealed an isolated right abducent nerve and right hypoglossal nerve palsy, with other cranial nerves intact. Neuroimaging revealed a right clival mass. Supraorbital craniotomy and tumour debulking were done in the same year. Histopathological examination showed low-grade chondrosarcoma. After 5-years of default, he came back with the tumour enlarged. He underwent a right orbitozygomatic craniotomy and tumour excision with 33 cycles of radiotherapy. Despite two surgeries and radiotherapy, the abducent nerve and hypoglossal nerve did not improve throughout 6 years of follow-up. Cranial nerve VI palsy is not always a false localizing sign, in Godtfredsen syndrome it serves as a localizing sign.

CONCLUSION

To the best of our knowledge, this is the first case report of Godtfredsen Syndrome secondary to clival chondrosarcoma. Cranial nerve VI and XII palsy with no involvement of other cranial nerves, most likely the pathology is located at the clivus.

Microsurgical Anatomy of the Hypoglossal Nerve in the Lateral Approaches to the Craniovertebral Junction: A Study on Fresh Non-Formalin-Fixed Human Specimens

The aim of this anatomical study is to describe the anatomy of the hypoglossal nerve (HN) from its origin to the extracranial portion as it appears by performing a combined posterolateral and anterolateral approach to the craniovertebral junction (CVJ). Twelve fresh, non-formalin-fixed adult cadaveric heads (24 sides) were analyzed for the simulation of the combined lateral approach to the CVJ. The HN is divided into three main parts: cisternal, intracanalicular, and extracranial The anatomical relationships between the HN and other nerves, muscles, arteries and veins were carefully recorded, and some measurements were made between the HN and related structures. Thus, various landmarks were determined for the easy identification of the HN. Understanding the detailed anatomy of the HN and its relationships with the surrounding structures is crucial to prevent some complications during CVJ surgery.

Irreversible Hypoglossal Nerve Injury and Concomitant Trigeminal System Dysfunction After Anterior Surgery to the Cervical Spine: Case Report and Literature Review

BACKGROUND

The anterior surgical approach to the cervical spine is known to be safe, and damage to the hypoglossal nerve and trigeminal pathway after the surgery is uncommon. However, once damage to those nerves occurs, the patient's quality of life can be severely impaired by discomfort and disability.

CASE DESCRIPTION

We report the case of a 59-year-old male with concomitant and irreversible hypoglossal nerve and trigeminal system dysfunction after cervical spine surgery by the anterior approach confirmed by an electrodiagnostic study. He had undergone anterior cervical disc fusion through right-sided approach for a herniated intervertebral disc on the C3-4 level and direct cord compression. He had difficulty with tongue movement, dysarthria, and hypesthesia along the lower margin of the right mandible immediately after the surgery. An electrodiagnostic study revealed hypoglossal neuropathy and trigeminal somatosensory pathway dysfunction. Even though the patient received rehabilitation therapy for impaired tongue movement for more than 2 years, this function did not recover.

CONCLUSIONS

It is important to be aware of the complexity of the anatomy of vulnerable structures, including hypoglossal nerves and the trigeminal nerve system at the cervical spine level, to prevent damage to important neural structures during surgical procedures.

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.

Ipsilateral hypoglossal nerve palsy following left hemithyroidectomy: Case report and review of literature

INTRODUCTION

Hypoglossal nerve palsy (HNP) is a rare complication of airway management. Multiple factors have been postulated to contribute to its occurrence. Herein, we present a case of ipsilateral HNP following left hemithyroidectomy.

CASE PRESENTATION

A 47-year-old women presented complaining of left thyroid swelling for 1 year with no symptoms of compression or hormonal impairment. Ultrasound of the neck showed a 3 × 2 cm nodule in the left thyroid lobe without lymphadenopathy. Fine-needle aspiration revealed a follicular neoplasm. Left hemithyroidectomy was carried out uneventfully. Three hours postoperatively, the patient started to complaint of dysarthria, dysphagia and odynophagia with clinical sign of tongue deviation to the left side. Head and neck CT ruled out mass effect or ischemic event, and the diagnosis of left HNP was established. Four months postoperatively, the palsy was completely resolved. Histopathology examination of the thyroid nodule showed follicular adenoma, and no further intervention was provided.

DISCUSSION

Few cases of HNP are reported in the literature following oropharyngeal manipulation. Factors such as the type of surgery, position changes, and intubation characteristics have been linked to the incidence of HNP. Most of the cases recovered spontaneously, indicating a neuro-paxic type of injury. One case of HNP was reported following robotic total thyroidectomy, which was referred to as iatrogenic complication, and resulted in permanent paralysis. We believe that our case is the only reported case of transient ipsilateral HNP following a conventional left hemithyroidectomy.

CONCLUSION

Strap muscles retraction and neck extension during thyroidectomy could predispose to HNP.

Surgical Anatomy of the Cervical Part of the Hypoglossal Nerve

Iatrogenic injuries to cranial nerves, half of which affect the hypoglossal nerve, occur in up to 20% of surgical procedures involving the neck. The risk of injury could be minimized by in-depth knowledge of its positional and relational anatomy. Forty-one hypoglossal nerves were dissected from cadaveric specimens and positions described in relation to the internal carotid artery (ICA), external carotid artery (ECA), carotid bifurcation, mandible, hyoid bone, mastoid process, and the digastric tendon. The distance of the nerve from where it crossed the ICA and ECA to the carotid bifurcation was 29.93 (±5.99) mm and 15.19 (±6.68) mm, respectively. The point where it crossed the ICA was 12.24 (±3.71) mm superior to the greater horn of hyoid, 17.16 (±4.40) mm inferior to the angle of the mandible, and 39.08 (±5.69) mm from tip of the mastoid. The hypoglossal nerve loop was inferior to the digastric tendon in 73% of the cases. The hypoglossal nerves formed high loops in this study population. Caution should be exercised during surgical procedures in the neck. The study also revealed that the mastoid process is a reliable fixed landmark to locate the hypoglossal nerve.

Microsurgical Anatomy of the Hypoglossal and C1 Nerves: Description of a Previously Undescribed Branch to the Atlanto-Occipital Joint

OBJECTIVE

Distal branches of the C1 nerve that travel with the hypoglossal nerve have been well investigated but relationships of C1 and the hypoglossal nerve near the skull base have not been described in detail. Therefore, the aim of this study was to investigate these small branches of the hypoglossal and first cervical nerves by anatomic dissection.

METHODS

Twelve sides from 6 cadaveric specimens were used in this study. To elucidate the relationship among the hypoglossal, vagus, and first and cervical nerve, the mandible was removed and these nerves were dissected under the surgical microscope.

RESULTS

A small branch was found to always arise from the dorsal aspect of the hypoglossal nerve at the level of the transverse process of the atlas and joined small branches from the first and second cervical nerves. The hypoglossal and C1 nerves formed a nerve plexus, which gave rise to branches to the rectus capitis anterior and rectus capitis lateralis muscles and the atlanto-occipital joint.

CONCLUSIONS

Improved knowledge of such articular branches might aid in the diagnosis and treatment of patients with pain derived from the atlanto-occipital joint. We believe this to be the first description of a branch of the hypoglossal nerve being involved in the innervation of this joint.

Sternocleidomastoid innervation from an aberrant nerve arising from the hypoglossal nerve: a prospective study of 160 neck dissections

BACKGROUND

Anatomical variants of the spinal root of the accessory nerve and cervical plexus are well known but other variants are exceptionally rare.

METHODS

A prospective study of 160 selective neck dissections was undertaken following an index case, where a presumed C1 nerve (travelling with the hypoglossal nerve) was found to innervate sternocleidomastoid (SCM). A search was subsequently made for this variant while not compromising the neck dissection surgery itself. Eight cases could not be included due to metastatic disease precluding safe dissection in this area. A nerve stimulator was used to confirm the motor supply to SCM.

RESULTS

This nerve variant was found in 4/160 necks (2.5 %). In all cases, it originated directly from the hypoglossal nerve and stimulation resulted in isolated SCM contraction. No accessory nerve anomalies were found.

CONCLUSION

This finding adds to the knowledge of variants in this area. Meticulous dissection and preservation of all nerves, where possible, is important for optimising functional outcomes following surgery.

C1 Lateral Mass Screw Migration Causing a Delayed Unilateral Hypoglossal Nerve Lesion: A Case Report

CASE

We present the case of a fifty-eight-year-old woman who was initially treated with a C1 to C7 anterior-posterior cervical decompression and fusion for an epidural abscess and returned two years postoperatively with four days of progressive dysphagia and tongue deviation. She was diagnosed with a unilateral hypoglossal nerve (cranial nerve XII) palsy secondary to compression from a C1 lateral mass screw.

CONCLUSION

This is the first reported case that we are aware of describing a delayed cranial nerve palsy secondary to cutout and cephalad migration of a C1 lateral mass screw resulting in a neurologic deficit due to impingement on the hypoglossal nerve.

Isolated partial, transient hypoglossal nerve injury following acupuncture

We report a case of isolated unilateral hypoglossal nerve injury following ipsilateral acupuncture for migraines in a 53-year-old lady. The palsy was partial, with no associated dysarthria, and transient. Further examination and imaging was negative. Cranial nerve injuries secondary to acupuncture are not reported in the literature, but are a theoretical risk given the location of the cranial nerves in the neck. Anatomical knowledge is essential in those administering the treatment, and those reviewing patients with possible complications.

Solitary paraganglioma of the hypoglossal nerve: A case report with magnetic resonance imaging findings

Patient: Female, 58

Final Diagnosis: Solitary paraganglioma of the hypoglossal nerve

Symptoms: Neck pain

Medication: —

Clinical Procedure: Surgical resection

Specialty: Otolaryngology

Anatomic connections of the diaphragm: influence of respiration on the body system

The article explains the scientific reasons for the diaphragm muscle being an important crossroads for information involving the entire body. The diaphragm muscle extends from the trigeminal system to the pelvic floor, passing from the thoracic diaphragm to the floor of the mouth. Like many structures in the human body, the diaphragm muscle has more than one function, and has links throughout the body, and provides the network necessary for breathing. To assess and treat this muscle effectively, it is necessary to be aware of its anatomic, fascial, and neurologic complexity in the control of breathing. The patient is never a symptom localized, but a system that adapts to a corporeal dysfunction.

Tongue anatomy and physiology, the scientific basis for a novel targeted neurostimulation system designed for the treatment of obstructive sleep apnea

INTRODUCTION

 Obstructive sleep apnea (OSA) is a chronic condition that affects millions adults. The effective standard treatment is positive airway pressure (PAP). However, approximately half of the patients that are prescribed PAP are unable or unwilling to comply with this therapy. Untreated OSA ultimately leads to very serious comorbidities. An alternative therapy for this patient population, therefore, is desirable. Hypoglossal nerve (HGN) stimulation is under investigation by multiple groups as a possible alternative therapy for OSA.

OBJECTIVE

To understand the underlying mechanisms of actions related to HGN stimulation, and the implication of this knowledge for specifying and designing a neurostimulation system for the treatment of OSA.

RESULTS

 Loss of lingual and pharyngeal tone within a narrow airway is the primary mechanism for OSA. Posterior and anterior tongues are different in their anatomy and physiology. Muscle fibers in the posterior tongue are predominantly fatigue resistant that are responsible for the long sustained tonic activities required for maintaining the tongue's position and preventing its mass from falling into the retroglossal airway. The human tongue is a muscular hydrostat and hence would benefit from a sophisticated HGN stimulation system that is capable of achieving a concerted spatio-temporal interplay of multiple lingual muscles, including retrusors.

CONCLUSION

 Targeted neurostimulation of the proximal HGN presents as a viable system approach that is far more versatile and physiologic and quite different than prior systems.

Isolated unilateral hypoglossal nerve palsy due to vertebral artery dissection

We report the case of a patient with unilateral tongue weakness secondary to an isolated lower motor neuron hypoglossal nerve palsy that was caused by a right vertebral artery dissection in the lower neck. The patient had a boggy tongue with a deviation to the right side but an otherwise normal neurological examination. Magnetic resonance angiography showed a narrow lumen of the right vertebral artery in the neck. After initially treating the patient with aspirin in the emergency room and later with warfarin for three months, there was complete recanalization of the right vertebral artery. Only one other case of vertebral artery dissection and twelfth nerve palsy has been reported before.

The unusual origin of the sternocleidomastoid artery from the lingual artery

The sternocleidomastoid (SCM) artery supplying blood to the SCM muscle has different origins according to its anatomical segment. The authors performed cadaveric neck dissection to review the surgical anatomy of neurovascular structures surrounding the carotid artery in the neck. During the dissection, an unusual finding was cited in which the SCM artery supplying the middle part of the SCM muscle originated from the lingual artery (LA); it was also noted that it crossed over the hypoglossal nerve (HN). There have been extremely rare reports citing the SCM artery originated from the LA. Though the elevation of the HN over the internal carotid artery was relatively high, the vascular loop crossing over the HN was very close to the carotid bifurcation. Special anatomical consideration is required to avoid the injury of the HN during carotid artery surgery.

Hypoglossal Nerve Stimulation and Airway Changes under Fluoroscopy

Objective. To characterize the changes in the anteroposterior dimensions of both the retropalatal and retrolingual airway spaces of the pharynx and hyoid bone position during hypoglossal nerve stimulation under general anesthesia in subjects with obstructive sleep apnea.

Study Design. Cross-sectional.

Setting. Academic center.

Subjects and Methods. Cross-table fluoroscopic images obtained during hypoglossal nerve stimulation were studied in 26 subjects enrolled in the Apnex Medical Hypoglossal Nerve Stimulation (HGNS) system feasibility trials. Changes in the anteroposterior dimensions (2-dimensional) of the retropalatal and retrolingual airway spaces and hyoid bone position were recorded. Measurements were estimated in millimeters and standardized to each subject’s C3 vertebral height. Opening of the pharyngeal airspace was examined relative to body mass index.

Results. During hypoglossal nerve stimulation, all subjects demonstrated anterior displacement of the tongue base on fluoroscopy. The average retrolingual airway opening was 0.71 ± 0.23 C3 vertebral body heights (9 ± 3 mm). Opening of the retropalatal airway with stimulation occurred in 65% (15/23) of subjects. When present, the average opening was 0.42 ± 0.14 vertebral heights (5 ± 3 mm). Anterior displacement of the hyoid occurred in 92% (23/25) of subjects. Retrolingual airway opening was independent of baseline body mass index.

Conclusion. Unilateral hypoglossal nerve stimulation results in anterior tongue base displacement and an increase in the anterior-posterior retrolingual airway dimensions of the pharynx, independent of body mass index. Opening of the retropalatal airway occurred in a majority of subjects and had a trend toward correlation with body mass index.

Minimally invasive supracondylar transtubercular (MIST) approach to the lower clivus

OBJECTIVE

Drawbacks of the far-lateral approach to the lower clivus and pontomedullary region include the morbidity of a large incision extending into the cervical musculature and tedious exposure of the vertebral artery (VA), particularly when performing the transcondylar and transtubercular extensions. The authors describe a minimally invasive alternative to the far-lateral approach that has the potential to minimize operative morbidity and decrease the need for VA manipulation.

METHODS

The minimally invasive supracondylar transtubercular (MIST) and far-lateral supracondylar transtubercular (FLST) approaches were performed in 10 adult cadaveric specimens (20 sides). The microsurgical anatomy of each step and the surgical views were analyzed and compared. In addition, the endoscopic view through the MIST was examined in five fresh cadaveric specimens (10 sides).

RESULTS

The MIST approach provided exposure of the inferior-middle clivus, the anterolateral brainstem, and the premedullary cisterns, including the PICA-VA and vertebrobasilar junctions. The endoscope provided a clear view of cranial nerves III through XII, as well as the vertebrobasilar system. The FLST approach increased visualization of the anterolateral margin of the foramen magnum; otherwise, the surgical view is similar between the MIST and FLST approaches.

CONCLUSIONS

The MIST approach could be considered as a potential alternative to the FLST approach in the treatment of lesions involving the inferior and middle clivus, and anterolateral lower brainstem; it does not require a C1 laminectomy, significant disruption of the atlanto-occipital joint, nor extensive exposure of the extracranial VA. Moreover, the MIST approach is an ideal companion to endoscope-assisted neurosurgery.

Metastatic disease causing unilateral isolated hypoglossal nerve palsy

The authors present the case of a middle-aged woman diagnosed with lobar carcinoma in situ in her right breast. She eventually underwent a mastectomy and reconstruction. Histology revealed grade II invasive ductal carcinoma and she was commenced on adjuvant letrozole. The following year a MRI scan revealed she had developed spinal metastases and CT confirmed the presence of liver and lung metastases. She presented with a 5-month history of tongue weakness and difficulty manipulating food to the back of her mouth. On examination, there was marked right-sided hemiatrophy of the tongue with deviation of the tongue to the right side upon protrusion. MRI demonstrated ill-defined enhancing material close to the intracranial opening of the right hypoglossal canal. The patient was referred for consideration of radiotherapy. Due to the comorbidities of the patient, she was not a candidate for neurosurgical intervention.

The existence of hypoglossal root ganglion cells in adult humans: potential clinical implications

INTRODUCTION

Ganglion cells of the hypoglossal nerve (HN) have been confirmed in certain animals but have been thought not to be present in man. To investigate for the presence of these structures in adult humans and if present, to verify their functionality, the present study was performed.

MATERIALS AND METHODS

We harvested adult cadaveric HN and observed for ganglion cells. Histological and immunohistochemical analyses were performed on all specimens.

RESULTS

Ganglion cells were found in 33% of specimens. Using immunohistochemistry, we found that these ganglia were sympathetic in nature. Based on our findings, ganglion cells do exist in the human HN although they are located sporadically and are found inconstantly.

CONCLUSIONS

Such information may be valuable in elucidating other functions of the HN and may aid in the histological diagnosis of this nerve. Additionally, pathology involving HN such as paragangliomas, are supported by our findings of the presence of autonomic ganglion cells in some HN specimens.