Imaging of denervation in the head and neck

ESR Essentials: pseudolesions in head and neck-practice recommendations by the European Society of Head and Neck Radiology

The differentiation between pathological and physiological entities constitutes a fundamental aspect of daily radiological practice. Pseudolesions manifest as a transient phenomenon within this spectrum, displaying features of pathology within the context of normal or variant anatomy. A variety of structures, including vascular components, ectopic formations, or deviations from typical developmental patterns, can mimic pathological entities. It is crucial to discern between the two: lesions warranting treatment or ongoing radiological monitoring and pseudolesions where further analysis or treatment is unnecessary. Radiology plays a key role in classifying these entities. Comprehensive knowledge and accurate assessment of head and neck pseudolesions are necessary for radiologists to avoid unnecessary further diagnostic tests, treatments, and distress for the patient. KEY POINTS: Pseudolesions are an aspect of typical anatomy. Ectopic structures will have the same intensity/density no matter the location. Pursuit of a vascular origin can be a problem solver. Incorporate pseudolesions in the report.

Pictorial Review of Cranial Nerve Denervation in the Head and Neck

Of the twelve cranial nerves, nine supply motor innervation to the muscles of the head and neck. Loss of this motor nerve supply, or denervation, follows a series of predictable chronologic changes in the affected muscles. Although the length of time between each change is markedly variable, denervation is typically classified into three distinct time points: (a) acute, (b) subacute, and (c) chronic. These muscle changes produce characteristic findings on images, with contrast-enhanced MRI being the preferred modality for assessment. Imaging allows radiologists to not only identify denervation but also evaluate the extent of denervation and localize the potential site of insult. However, these findings may be easily mistaken for other diseases with similar manifestations, such as neoplasm, infection, and inflammatory conditions. As such, it is fundamental for radiologists to be familiar with cranial nerve anatomy and denervation patterns so that they can avoid these potential pitfalls and focus their imaging search on the pathway of the affected nerve. In this article, the anatomy and muscles innervated by motor cranial nerves in the head and neck, denervation, and the associated expected imaging patterns are reviewed, and examples of potential pitfalls and denervation mimics are provided. ©RSNA, 2024.

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.

A Strength Endurance Exercise Paradigm Mitigates Deficits in Hypoglossal-Tongue Axis Function, Strength, and Structure in a Rodent Model of Hypoglossal Motor Neuron Degeneration

The tongue plays a crucial role in the swallowing process, and impairment can lead to dysphagia, particularly in motor neuron diseases (MNDs) resulting in hypoglossal-tongue axis degeneration (e.g., amyotrophic lateral sclerosis and progressive bulbar palsy). This study utilized our previously established inducible rodent model of dysphagia due to targeted degeneration of the hypoglossal-tongue axis. This model was created by injecting cholera toxin B conjugated to saporin (CTB-SAP) into the genioglossus muscle of the tongue base for retrograde transport to the hypoglossal (XII) nucleus via the hypoglossal nerve, which provides the sole motor control of the tongue. Our goal was to investigate the effect of high-repetition/low-resistance tongue exercise on tongue function, strength, and structure in four groups of male rats: (1) control + sham exercise (n = 13); (2) control + exercise (n = 10); (3) CTB-SAP + sham exercise (n = 13); and (4) CTB-SAP + exercise (n = 12). For each group, a custom spout with adjustable lick force requirement for fluid access was placed in the home cage overnight on days 4 and 6 post-tongue injection. For the two sham exercise groups, the lick force requirement was negligible. For the two exercise groups, the lick force requirement was set to ∼40% greater than the maximum voluntary lick force for individual rats. Following exercise exposure, we evaluated the effect on hypoglossal-tongue axis function (via videofluoroscopy), strength (via force-lickometer), and structure [via Magnetic Resonance Imaging (MRI) of the brainstem and tongue in a subset of rats]. Results showed that sham-exercised CTB-SAP rats had significant deficits in lick rate, swallow timing, and lick force. In exercised CTB-SAP rats, lick rate and lick force were preserved; however, swallow timing deficits persisted. MRI revealed corresponding degenerative changes in the hypoglossal-tongue axis that were mitigated by tongue exercise. These collective findings suggest that high-repetition/low-resistance tongue exercise in our model is a safe and effective treatment to prevent/diminish signs of hypoglossal-tongue axis degeneration. The next step is to leverage our rat model to optimize exercise dosing parameters and investigate corresponding treatment mechanisms of action for future translation to MND clinical trials.

Magnetic resonance imaging of the caudal portion of the digastric muscle in canine idiopathic facial neuropathy

Idiopathic is the most common etiology for acute onset of facial neuropathy in dogs with limited number of studies describing MRI characteristics. A retrospective, observational study was performed using archived records, aiming to describe the MRI features of the caudal portion of the digastric muscle in dogs diagnosed with idiopathic facial neuropathy and to determine correlation with prognosis. Client-owned dogs presented to a referral hospital between 2009 and 2019, diagnosed with unilateral idiopathic facial neuropathy and having undergone MRI, with images including the caudal portion of the digastric muscle, were included (n = 19). MRI appearance of the affected muscle, including degree of muscle atrophy, signal intensity, enhancement post-contrast, and enhancement characteristics of the affected facial nerve, was described and compared to the contralateral, clinically unaffected caudal portion of the digastric muscle. Correlation between MRI appearance and outcome at 1-month and 3-months following onset of clinical signs was investigated. The majority of patients demonstrated some degree of muscle atrophy (n = 17, 89%), hyperintensity in T2W (n = 17, 89%), and pre-contrast T1W (n = 15, 79%) images, as well as contrast enhancement of the affected muscle (n = 14, 74%) and affected facial nerve (n = 9, 47%). There was no statistically significant correlation between atrophy or enhancement of the affected caudal portion of the digastric muscle nor between enhancement of the affected facial nerve and outcome. Hyperintensity both in T2W images and pre-contrast T1W images was significantly correlated with a worse prognosis. Ensuring inclusion and evaluation of this muscle in MRI may therefore be indicated in canine idiopathic facial neuropathy.

Extra-nodal extension in head and neck cancer: how radiologists can help staging and treatment planning

Extranodal extension (ENE) is a significant prognostic factor in p16-negative head and neck squamous-cell carcinoma and is classified as N3b by the American Joint Committee on Cancer 8th edition. While most previous radiological studies have focused on the diagnostic performance of pathological ENE, radiologists should be able to provide more clinically relevant information on this entity. The purpose of this article is to review the clinical implications of ENE, to describe key imaging features of ENE with clinical and histopathological correlations and to discuss evaluation of ENE for clinical staging, treatment planning, and predicting the response to treatment. First, we discuss the basics of ENE, including definitions of pathological and clinical ENE and its association with imaging findings. Second, we describe the ENE extension pattern at each location according to level system. The crucial structures determining the choice of treatment include the deep fascia in the deep cervical layer, internal and common carotid arteries, and mediastinal structures. Invasion of the muscles, internal jugular vein, nerves, or mandible also affect the surgical procedure. Finally, we discuss assessment of nodal metastasis after chemoradiotherapy.

Imaging Features of isolated hypoglossal nerve palsy

The hypoglossal nerve gives motor innervation to the intrinsic and extrinsic muscles of the tongue. Pathology of this nerve affects the balanced action of the genioglossus muscle causing tongue deviation toward the weak side. Clinically, hypoglossal nerve palsy manifests with difficulty chewing, swallowing and with dysarthric speech herein, we review the anatomy of the hypoglossal nerve as well as common and infrequent lesions that can affect this nerve along its course.

Guidelines for radiographic imaging of cranial neuropathies

Disruption of the complex pathways of the 12 cranial nerves can occur at any site along their course, and many, varied pathologic processes may initially manifest as dysfunction and neuropathy. Radiographic imaging (computed topography or magnetic resonance imaging) is frequently used to evaluate cranial neuropathies; however, indications for imaging and imaging method of choice vary considerably between the cranial nerves. The purpose of this review is to provide an analysis of the diagnostic yield and the most clinically appropriate means to evaluate cranial neuropathies using radiographic imaging. Using the PubMed MEDLINE NCBI database, a total of 49,079 articles' results were retrieved on September 20, 2014. Scholarly articles that discuss the etiology, incidence, and use of imaging in the context of evaluation and diagnostic yield of the 12 cranial nerves were evaluated for the purposes of this review. We combined primary research, guidelines, and best practice recommendations to create a practical framework for the radiographic evaluation of cranial neuropathies.

Tracking the glossopharyngeal nerve pathway through anatomical references in cross-sectional imaging techniques: a pictorial review

Abstract

The glossopharyngeal nerve (GPN) is a rarely considered cranial nerve in imaging interpretation, mainly because clinical signs may remain unnoticed, but also due to its complex anatomy and inconspicuousness in conventional cross-sectional imaging. In this pictorial review, we aim to conduct a comprehensive review of the GPN anatomy from its origin in the central nervous system to peripheral target organs. Because the nerve cannot be visualised with conventional imaging examinations for most of its course, we will focus on the most relevant anatomical references along the entire GPN pathway, which will be divided into the brain stem, cisternal, cranial base (to which we will add the parasympathetic pathway leaving the main trunk of the GPN at the cranial base) and cervical segments. For that purpose, we will take advantage of cadaveric slices and dissections, our own developed drawings and schemes, and computed tomography (CT) and magnetic resonance imaging (MRI) cross-sectional images from our hospital’s radiological information system and picture and archiving communication system.

Teaching Points

• The glossopharyngeal nerve is one of the most hidden cranial nerves.

• It conveys sensory, visceral, taste, parasympathetic and motor information.

• Radiologists’ knowledge must go beyond the limitations of conventional imaging techniques.

• The nerve’s pathway involves the brain stem, cisternal, skull base and cervical segments.

• Systematising anatomical references will help with nerve pathway tracking.

End-organ radiographic manifestations of cranial neuropathies: A concise review

BACKGROUND

Cranial neuropathies are a spectrum of disorders associated with dysfunction of one or more of the twelve cranial nerves and the subsequent anatomic structures they innervate.

OBJECTIVE

The purpose of this article is to review radiographic imaging findings of end-organ aberrations secondary to cranial neuropathies.

METHOD

All articles related to cranial neuropathies were retrieved through the PubMed MEDLINE NCBI database from January 1, 1991 to August 31, 2014. These manuscripts were analyzed for their relation to cranial nerve end-organ disease pathogenesis and radiographic imaging.

RESULTS

The present review reveals detectable end-organ changes on CT and/or MRI for the following cranial nerves: olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, accessory nerve, and hypoglossal nerve.

CONCLUSION

Radiographic imaging can assist in the detailed evaluation of end-organ involvement, often revealing a corresponding cranial nerve injury with high sensitivity and diagnostic accuracy. A thorough understanding of the distal manifestations of cranial nerve disease can optimize early pathologic detection as well as dictate further clinical management.

Uncommon and rare causes of vocal fold paralysis detected via imaging

BACKGROUND

Cross-sectional imaging can be used to trace the course of the vagus nerve and its laryngeal branches to detect many of the causes of vocal fold paralysis. The most frequent aetiologies are surgical injury and tumoural involvement of the recurrent laryngeal nerve anywhere along its course.

METHOD

This review article focuses on the uncommon and rare causes of vocal fold paralysis that have been detected or diagnosed on cross-sectional imaging.

RESULTS AND CONCLUSION

Uncommon causes included a tortuous oesophagus, tracheal diverticulum, cervical osteophytes and cardiovocal syndrome. These examples are presented with clinical case histories and radiological appearances, and are discussed in the context of the current literature.