Extracranial Hypoglossal Schwannoma: Case Report and Literature Review.

BACKGROUND: Schwannomas are solitary neurogenic tumors originating from the myelin sheath of peripheral nerves. Extracranial hypoglossal schwannomas comprise <5% of all head and neck schwannomas and can mimic submandibular salivary gland tumors. CASE REPORT: We report the diagnostic imaging, surgical treatment, and histopathological findings of a rare case of extracranial schwannoma of the hypoglossal nerve in a 73-year-old female, presented with an asymptomatic swelling in the left submandibular region that had been persisted for approximately three years. CONCLUSION: Accurate diagnosis of this rare clinical entity requires comprehensive diagnostics. The optimal therapeutic strategy is nerve-sparing surgical excision, although it can be challenging.

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.

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.

Yin-Yang tongue sign: An imaging clue of lesions involving the skull base segment in the hypoglossal pathway.

OBJECTIVE: To investigate the diagnostic value of the Yin-Yang tongue sign in patients with tongue deviation. METHODS: According to the presence of the Yin-Yang tongue sign on CT/MR, 107 patients with tongue deviation were divided into a positive group and a negative group. The involvement categories of the hypoglossal canal (HC) in the positive group were evaluated and classified as HC dilation and HC erosion. The correlations between HC involvement categories and the presence of the sign were analysed. RESULTS: There were 55 cases (55/107, 51.4%) in the positive group and 52 cases (52/107, 48.6%) in the negative group. Hypoglossal nerve (HN) involvement mainly occurred in the skull base (61.8%), skull base and carotid space (10.9%), and carotid space segment (12.7%). Neurogenic (50.9%), squamous cell carcinoma (14.5%), and metastases (12.7%) were the predominant aetiologies. The sensitivity, specificity, and accuracy of this sign for suggesting skull base lesions around HC were 72.4%, 80.8%, and 76.6%, respectively. In the positive group, HC dilation was seen in 21 patients (21/55, 38.2%) and 21 cases were all benign. HC erosion were noted in 19 patients (19/55, 34.5%), of whom 12 cases were malignant. CONCLUSION: The Yin-Yang tongue sign is formed by unilateral tongue atrophy and fat infiltration caused by lesions in the HN pathway, especially compressive or invasive lesions involving the skull base segment.

Diagnosis and management of hypoglossal nerve-derived schwannoma in the floor of mouth: a case series.

BACKGROUND: Schwannomas or neurilemmomas are well-encapsulated, benign, solitary, and slow-growing tumors that originate from Schwann cells of the nerve sheath. Extracranial schwannoma is reported to have a relatively high incidence in the tongue while an extremely low incidence in the floor of mouth. In the current study, we presented the first case series of hypoglossal nerve-derived schwannoma in the floor of mouth in Asia. METHODS: A retrospective study of 9 surgical cases of hypoglossal nerve-derived schwannoma in the floor of mouth was performed. The patient and tumor characteristics were evaluated by physical, radiological and pathological examination. Details of operation and complications were also recorded. RESULTS: Hypoglossal nerve-derived schwannoma in the floor of mouth showed a well-defined boundary with a firm texture, smooth surface and good mobility on palpation. The median maximum diameter of the tumors was 4.3 cm (range 2.8-7.0 cm). The median operative time and bleeding volumes were 89.4 min (range 47-180 min) and 99.2 mL (range 15-200 mL), respectively. All cases received complete surgical excision. CONCLUSION: In this study, we presented the diagnosis and management of hypoglossal nerve-derived schwannoma in the floor of mouth for the first time in Asia. The study provided us with a recommendation for consideration of the diagnosis of hypoglossal schwannoma when a patient presents with a mass in the floor of mouth.

Malignant Nerve Sheath Tumor of the Hypoglossal Nerve in a Maltese Dog.

A 4 yr old male Maltese dog presented with a 1 wk history of intermittent neck pain and progressive difficulty walking. Neurologic evaluation was consistent with a left-sided brainstem lesion. On oral examination, left lingual hemiatrophy was evident suggesting hypoglossal nerve involvement. A dumbbell-shaped extra-axial mass in the left side of the caudal fossa extending extracranially through the hypoglossal canal was detected by MRI. At postmortem histologic examination, the hypoglossal nerve was diffusely infiltrated by fusiform neoplastic cells arranged in Antoni A and Antoni B patterns. This is the first description of a malignant nerve sheath tumor selectively involving the hypoglossal nerve in a dog.

Isolated Hypoglossal Nerve Palsy as an Early Symptom of a Granular Cell Tumor.

BACKGROUND: Hypoglossal nerve palsy (HNP) is rather common as a neurological disease. However, as an isolated nerve palsy it is an exceedingly rare phenomenon and points at local pathologies along the peripheral course of the nerve. In this communication we report a granular cell tumor (GCT) arising in the submandibular segment of the hypoglossal nerve. CASE-REPORT: Spontaneous isolated HNP was recognized in a female patient. First line MR-imaging identified a clivus-chordoma. However, involvement of the hypoglossal nerve was highly unlikely according to MR-findings. Finally, ultrasonographic investigation revealed a small submandibular mass which, at histological examination, turned out to be a granular cell tumor arising within the hypoglossal nerve. CONCLUSIONS: This is the report of an extremely rare GCT originating within the 12th cranial nerve. The case illustrates that isolated motoric cranial nerve palsy may result from this rare tumor entity. This report also points out the diagnostic value of a simple ultrasonographic investigation to depict pathologic lesions of the submandibular space.

Hypoglossal Nerve Lesions: The Role of a 3D IR-Prepped Fast SPGR High-Resolution 3T MRI Sequence.

BACKGROUND AND PURPOSE: To assess a 3D high-resolution IR-prepped fast SPGR high-resolution MRI sequence for evaluating hypoglossal nerve lesions. METHODS: The clinical data of 8 patients with hypoglossal nerve lesions admitted from December 2011 to February 2016 were retrospectively analyzed. MRI included contrast-enhanced conventional sequences and a 3D IR-prepped fast SPGR high-resolution T1-weighted (BRAVO) MRI sequence at 3T. RESULTS: Eight patients had hypoglossal lesions detected by MRI. Conventional enhanced scanning could not clearly display the hypoglossal nerve and canal, while the enhanced 3D high-resolution sequence could. In addition, multiple planar reconstruction clearly displayed the hypoglossal nerve, hypoglossal canal, and lesions in multiple planes. CONCLUSIONS: Compared with conventional MRI, we show superior results from an advanced sequence to improve image quality in characterizing hypoglossal nerve lesions.

Size-dependent dendritic maladaptations of hypoglossal motor neurons in SOD1G93A mice.

The total motor neuron (MN) somato-dendritic surface area is correlated with motor unit type. MNs with smaller surface areas innervate slow (S) and fast fatigue-resistant (FR) motor units, while MNs with larger surface areas innervate fast fatigue-intermediate (FInt) and fast fatigable (FF) motor units. Differences in MN surface area (equivalent to membrane capacitance) underpin the intrinsic excitability of MNs and are consistent with the orderly recruitment of motor units (S > FR > FInt > FF) via the Size Principle. In amyotrophic lateral sclerosis (ALS), large MNs controlling FInt and FF motor units exhibit earlier denervation and death, compared to smaller and more resilient MNs of type S and FR motor units that are spared until late in ALS. Abnormal dendritic morphologies in MNs precede neuronal death in human ALS and in rodent models. We employed Golgi-Cox methods to investigate somal size-dependent changes in the dendritic morphology of hypoglossal MNs in wildtype and SOD1G93A mice (a model of ALS), at postnatal (P) day ~30 (pre-symptomatic), ~P60 (onset), and ~P120 (mid-disease) stages. In wildtype hypoglossal MNs, increased MN somal size correlated with increased dendritic length and spines in a linear fashion. By contrast, in SOD1G93A mice, significant deviations from this linear correlation were restricted to the larger vulnerable MNs at pre-symptomatic (maladaptive) and mid-disease (degenerative) stages. These findings are consistent with excitability changes observed in ALS patients and in rodent models. Our results suggest that intrinsic or synaptic increases in MN excitability are likely to contribute to ALS pathogenesis, not compensate for it.

Responses evoked by electrical stimulation of the brainstem reticular formation in the jaw-opening and hypoglossal motor nerves of an arterially perfused rat preparation.

The interneuronal system in the brainstem reticular formation plays an important role in elaborate muscle coordination during various orofacial motor behaviors. In this study, we examined the distribution in the brainstem reticular formation of the sites that induce monosynaptic motor activity in the mylohyoid (jaw-opening) and hypoglossal nerves using an arterially perfused rat preparation. Electrical stimulation applied to 286 and 247 of the 309 sites in the brainstem evoked neural activity in the mylohyoid and hypoglossal nerves, respectively. The mean latency of the first component in the mylohyoid nerve response was significantly shorter than that in the hypoglossal nerve response. Moreover, the latency histogram of the first component in the hypoglossal nerve responses was bimodal, which was separated by 4.0 ms. The sites that induced short-latency (<4.0 ms) motor activity in the mylohyoid nerve and the hypoglossal nerve were frequently distributed in the rostral portion and the caudal portion of the brainstem reticular formation, respectively. Such difference in distributions of short-latency sites for mylohyoid and hypoglossal nerve responses likely corresponds to the distribution of excitatory premotor neurons targeting mylohyoid and hypoglossal motoneurons.

Respiratory pathology in the Optn-/- mouse model of Amyotrophic Lateral Sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disorder that results in death due to respiratory failure. Many genetic defects are associated with ALS; one such defect is a mutation in the gene encoding optineurin (OPTN). Using an optineurin null mouse (Optn-/-), we sought to characterize the impact of optineurin deficiency on respiratory neurodegeneration. Respiratory function was assessed at 6 and 12 mo of age using whole body plethysmography at baseline during normoxia (FiO2: 0.21; N2 balance) and during a respiratory challenge with hypoxia and hypercapnia (FiCO2: 0.07, FiO2: 0.10; N2 balance). Histological analyses to assess motor neuron viability and respiratory nerve integrity were performed in the medulla, cervical spinal cord, hypoglossal nerve, and phrenic nerve. Minute ventilation, peak inspiratory flow, and peak expiratory flow are significantly reduced during a respiratory challenge in 6 mo Optn-/-mice. By 12 mo, tidal volume is also significantly reduced in Optn-/- mice. Furthermore, 12mo Optn-/- mice exhibit hypoglossal motor neuron loss, phrenic and hypoglossal dysmyelination, and accumulated mitochondria in the hypoglossal nerve axons. Overall, these data indicate that Optn-/- mice display neurodegenerative respiratory dysfunction and are a useful model to study the impact of novel therapies on respiratory function for optineurin-deficient ALS patients.

Motor axonopathies in a mouse model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease caused by deleterious mutations in the DMD gene which encodes the dystrophin protein. Skeletal muscle weakness and eventual muscle degradation due to loss of dystrophin are well-documented pathological hallmarks of DMD. In contrast, the neuropathology of this disease remains understudied despite the emerging evidence of neurological abnormalities induced by dystrophin loss. Using quantitative morphological analysis of nerve sections, we characterize axonopathies in the phrenic and hypoglossal (XII) nerves of mdx mice. We observe dysfunction in these nerves - which innervate the diaphragm and genioglossus respectively - that we propose contributes to respiratory failure, the most common cause of death in DMD. These observations highlight the importance in the further characterization of the neuropathology of DMD. Additionally, these observations underscore the necessity in correcting both the nervous system pathology in addition to skeletal muscle deficits to ameliorate this disease.

Gradient subthalamic neurodegeneration and tau pathology in the hypoglossal nucleus as essential pathological markers of progressive supranuclear palsy - Richardson syndrome.

Progressive supranuclear palsy - Richardson syndrome (PSP-RS) was first described in 1964 by Steele et al. Tau pathology has not been reported in the hypoglossal nuclei of PSP-RS patients, whereas Steele et al. described gliosis with no remarkable neuronal losses in the hypoglossal nucleus. This study aimed to investigate the distribution and degree of tau pathology-associated neurodegeneration, with an emphasis on the hypoglossal nucleus, in patients with PSP-RS. Six clinicopathologically proven PSP-RS cases were included in this study. All patients were clinicopathologically and immunohistochemically re-evaluated. This study confirmed the following neuropathological characteristics of PSP-RS: (1) neurodegeneration usually affects the striatonigral system and cerebellar dentate nucleus; (2) the cerebellar afferent system in PSP-RS is affected by absent-to-mild neurodegeneration; and (3) the extent of tau distribution throughout the central nervous system is greater than the extent of neurodegeneration. Furthermore, we found that subthalamic neurodegeneration was more prominent in the ventromedial region than in the dorsolateral region. Nevertheless, the tau pathology showed no remarkable differences between these two sites. Interestingly, the tau pathology was frequently observed in the hypoglossal nuclei of PSP-RS patients. Gradient neurodegeneration of the subthalamus and tau pathology in the hypoglossal nucleus could be regarded as essential pathological features of PSP-RS.

Isolated hypoglossal nerve palsy due to a jugular foramen schwannoma.

Introduction - Although the involvement of the hypoglossal nerve together with other cranial nerves is common in several pathological conditions of the brain, particularly the brainstem, isolated hypoglossal nerve palsy is a rare condition and a diagnostic challenge. Case presentation - The presented patient arrived to the hospital with a history of slurred speech and an uncomfortable sensation on his tongue. Neurological examination showed left-sided hemiatrophy of the tongue with fasciculations and deviation towards the left side during protrusion. Based on the clinical and MRI findings, a diagnosis of hypoglossal nerve schwannoma was made. Discussion - Hypoglossal nerve palsy may arise from multiple causes such as trauma, infections, neoplasms, and endocrine, autoimmune and vascular pathologies. In our case, the isolated involvement of the hypoglossal nerve was at the skull base segment, where the damage to the hypoglossal nerve may occur mostly due to metastasis, nasopharyngeal carcinomas, nerve sheath tumors and glomus tumors. Conclusion - Because of the complexity of the region's anatomy, the patient diagnosed with hypoglossal nerve schwannoma was referred for gamma knife radiosurgery.

Incidence and outcomes of radiation-induced late cranial neuropathy in 10-year survivors of head and neck cancer.

OBJECTIVES: To characterize the late cranial neuropathy among 10-year survivors of head and neck cancer treatment. MATERIALS AND METHODS: We retrospectively evaluated patients treated with curative-intent radiation for HNC between 1990 and 2005 at a single institution with systematic multidisciplinary follow-up ≥ 10 years. New findings of CNP were considered radiation-induced when examination, imaging and/or biopsy did not demonstrate a structural or malignant cause. Cox proportional hazards modeling was used for univariable analysis (UVA) and multivariable analysis (MVA) for time to CNP after completion of radiation. RESULTS: We identified 112 patients with no evidence of disease and follow-up ≥ 10 years (median 12.2). Sixteen (14%) patients developed at least one CNP. The median time to CNP was 7.7 years (range 0.6-10.6 years). Most common was CN XII deficit in eight patients (7%), followed by CN X deficit in seven patients (6%). Others included CN V deficit in three, and CN XI deficit in two. Eight of the thirteen patients with a CN X and/or CN XII deficit required a permanent gastrostomy tube. On UVA, site of primary disease, post-radiation neck dissection, chemotherapy, and radiation dose were significantly associated with increased risk of CNP. CONCLUSION: Iatrogenic CNP may develop years after head and neck cancer treatment and often leads to swallowing dysfunction. Long-term follow up is essential for these patients receiving head and neck radiation.

Report of a non-looped variant of ansa cervicalis with omohyoid innervation from accessory nerve branch and omohyoid attachment to mastoid process.

INTRODUCTION: A variant of the innervation of the infrahyoid neck musculature is reported in which the typical looped ansa cervicalis structure is absent. In this variant, the infrahyoid muscles (sternohyoid, sternothyroid omohyoid and thyrohyoid) were innervated by a presumptive superior root of "ansa cervicalis" traveling with vagus nerve (CN X) and not branching from hypoglossal nerve (CN XII). The omohyoid muscle, typically innervated by the inferior root of ansa cervicalis, is instead innervated by nerve fibers branching from the accessory nerve (CN XI). This formation created a non-looping variant of ansa cervicalis. Furthermore, the omohyoid muscle did not attach to the hyoid bone but instead attached to the mastoid process of the temporal bone by merging its fibers superiorly and posteriorly with the clavicular portion of the sternocleidomastoid muscle, creating a "sternocleidoomomastoid" muscle innervated by a branch of accessory nerve. MATERIALS AND METHODS: This variation was found in one black male cadaver from a cohort of 25 male and female cadavers. RESULTS: Only one variation of ansa cervicalis was observed. CONCLUSIONS: As neck dissections and surgical procedures of this region are performed for a variety of conditions-including coronary artery bypass grafting and metastatic neck disease-variations of this type are of broad clinical surgical importance.

Effect of surgically guided axonal regrowth into a 3-way-conduit (isogeneic trifurcated aorta) on functional recovery after facial-nerve reconstruction: Experimental study in rats.

BACKGROUND: The "post-paralytic syndrome" after facial nerve reconstruction has been attributed to (i) malfunctioning axonal guidance at the fascicular (branches) level, (ii) collateral branching of the transected axons at the lesion site, and (iii) intensive intramuscular terminal sprouting of regenerating axons which causes poly-innervation of the neuromuscular junctions (NMJ). OBJECTIVE: The first two reasons were approached by an innovative technique which should provide the re-growing axons optimal conditions to elongate and selectively re-innervate their original muscle groups. METHODS: The transected facial nerve trunk was inserted into a 3-way-conduit (from isogeneic rat abdominal aorta) which should "guide" the re-growing facial axons to the three main branches of the facial nerve (zygomatic, buccal and marginal mandibular). The effect of this method was tested also on hypoglossal axons after hypoglossal-facial anastomosis (HFA). Coaptational (classic) FFA (facial-facial anastomosis) and HFA served as controls. RESULTS: When compared to their coaptation (classic) alternatives, both types of 3-way-conduit operations (FFA and HFA) promoted a trend for reduction in the collateral axonal branching (the proportion of double- or triple-labelled perikarya after retrograde tracing was slightly reduced). In contrast, poly-innervation of NMJ in the levator labii superioris muscle was increased and vibrissal (whisking) function was worsened. CONCLUSIONS: The use of 3-way-conduit provides no advantages to classic coaptation. Should the latter be impossible (too large interstump defects requiring too long interpositional nerve grafts), this type of reconstruction may be applied. (230 words).

Paresia idiopática del nervio hipogloso / Isolated hypoglossal nerve palsy

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Hypoglossal canal schwannoma causing isolated left 12th cranial nerve palsy.

A 40-year-old woman presented with insidious onset, gradually progressive dysarthria and inability to manoeuvre bolus of food in her mouth while eating. The duration of her symptoms was 3 months. On evaluation, the left half of her tongue was wasted. The tongue deviated to the left on protrusion. There were no clinical features suggestive of involvement of the ipsilateral 9th, 10th or 11th cranial nerves. MRI of the brain showed a large, fusiform lesion in the left hypoglossal canal, extending into the jugular canal. The lesion was surgically excised and found to be a schwannoma.