Evaluating the upper airway with standardized magnetic resonance imaging

TORS for OSA: a practice, pitfalls and literature review

PURPOSE

Trans-oral robotic surgery (TORS) is increasingly employed in obstructive sleep apnoea (OSA) management. Objective outcomes are generally assessed through polysomnography. Pre-operative magnetic resonance imaging (MRI) can be a useful adjunct in objective upper airway assessment, in particular the tongue base, providing useful information for surgical planning and outcome assessment, though care must be taken in patient positioning during surgery. The purpose of this paper is to identify pitfalls in this process and suggest a protocol for pre-operative MRI scanning in OSA.

DESIGN/METHODOLOGY/APPROACH

This study is a four-patient prospective case-series and literature review. Outcome measures include pre- and post-operative volumetric changes in the pharynx as measured on MRI and apnoea-hypopnea indices (AHI), with cure being OSA resolution or a 50 per cent reduction in AHI.

FINDINGS

All patients achieved AHI reduction and/or OSA cure following TORS, despite a decrease in pharyngeal volume measurements at the tongue base level. This study and others lacked standardisation in the MRI scanning protocol, which resulted in an inability to effectively compare pre- and post-operative scans. Pitfalls were related to variation in head/tongue position, soft-tissue marker usage and assessed area boundary limits.

PRACTICAL IMPLICATIONS

TORS appears to be effective in OSA management. A new protocol for patient positioning and anatomical landmarks is suggested.

ORIGINALITY/VALUE

The findings could provide directly comparable data between scans and may allow correlation between tongue base volumetric changes and AHI through subsequent and historical study meta-analysis.

Anatomic measures of upper airway structures in obstructive sleep apnea

Objective

Determine if anatomic dimensions of airway structures are associated with airway obstruction in obstructive sleep apnea (OSA) patients.

Methods

Twenty-eight subjects with (n = 14) and without (n = 14) OSA as determined by clinical symptoms and sleep studies; volunteer sample. Skeletal and soft tissue dimensions were measured from radiocephalometry and magnetic resonance imaging. The soft palate thickness, mandibular plane-hyoid (MP-H) distance, posterior airway space (PAS) diameters and area, and tongue volume were calculated.

Results

Compared to controls, the OSA group demonstrated a significantly longer MP-H distance (P = 0.009) and shorter nasal PAS diameter (P = 0.02). The PAS area was smaller (P = 0.002) and tongue volume larger in the OSA group (P = 0.004). The MP-H distance, PAS measurements, and tongue volume are of clinical relevance in OSA patients.

Conclusions

A long MP-H distance, and small PAS diameters and area are significant anatomic measures in OSA; however the most substantial parameter found was a large tongue volume.

Volumetric tissue reduction in radiofrequency surgery of the tongue base

OBJECTIVES:

Radiofrequency surgery is a minimally invasive technique for the treatment of the tongue base in sleep-disordered breathing. The aim of this study was to evaluate the changes in upper airway anatomy induced by radiofrequency surgery with MRI.

STUDY DESIGN AND SETTING:

10 patients with sleep-disordered breathing were treated with radiofrequency surgery at tongue base. MRI measurements were performed before and after surgery with the help of a recently published protocol.

RESULTS:

The mean total number of energy delivered per patient was 4750 ± 1641 Joule. Relevant changes could be observed neither for tongue volume or dimension nor for retrolingual space.

CONCLUSIONS:

Changes in upper airway anatomy could not be demonstrated. The effects of radiofrequency surgery of the tongue base may more likely be a result of changes in upper airway collapsibility.

SIGNIFICANCE:

Functional effects of surgical interventions in sleep-disordered breathing should be considered in addition to mechanistic concepts alone.

Anatomic Changes After Hyoid Suspension for Obstructive Sleep Apnea: An MRI Study

OBJECTIVE: To assess the effects of isolated hyoid suspension on subjective and objective parameters of obstructive sleep apnea and to evaluate changes in upper airway anatomy with the help of standardized magnetic resonance imaging.

STUDY DESIGN AND SETTING: Fifteen patients received isolated hyoid suspension. Changes in respiratory disturbance index were assessed with polysomnography, and anatomical changes with standardized magnetic resonance imaging. Snoring, daytime sleepiness, and functional parameters were assessed with questionnaires. Lateral x-ray cephalometry was performed preoperatively.

RESULTS: Mean respiratory disturbance index was reduced from 35.2 ± 19.1 to 27.4 ± 26.2. Forty percent of the patients were classified as responders. Daytime sleepiness improved significantly. Relevant changes in upper airway anatomy could not be detected. There were no remarkable differences between responders and nonresponders in regard to imaging.

CONCLUSIONS: Hyoid suspension is effective only in a subgroup of patients and does not lead to relevant changes in airway diameters in the awake patient. Magnetic resonance imaging and x-ray cephalometry do not add additional information for patient selection.

SIGNIFICANCE: The reported clinical effects of hyoid suspension are more likely due to functional changes in airway collapsibility than to an enlargement of the upper airway.

Change in tongue morphology in response to expiratory resistance loading investigated by magnetic resonance imaging

[Purpose] The purpose of this study was to investigate the effect of expiratory resistance load on the tongue area encompassing the suprahyoid and genioglossus muscles. [Subjects] The subjects were 30 healthy individuals (15 males, 15 females, mean age: 28.9 years). [Methods] Magnetic resonance imaging was used to investigate morphological changes in response to resistive expiratory pressure loading in the area encompassing the suprahyoid and genioglossus muscles. Images were taken when water pressure was sustained at 0%, 10%, 30%, and 50% of maximum resistive expiratory pressure. We then measured tongue area using image analysis software, and the morphological changes were analyzed using repeated measures analysis of variance followed by post hoc comparisons. [Results] A significant change in the tongue area was detected in both sexes upon loading. Multiple comparison analysis revealed further significant differences in tongue area as well as changes in tongue area in response to the different expiratory pressures. [Conclusion] The findings demonstrate that higher expiratory pressure facilitates greater reduction in tongue area.

Comparison of the area of the pharynx during wakefulness and induced sleep in patients with Obstructive Sleep Apnea (OSA)

The study of obstructive sleep apnea (OSA) has received growing attention over the past years since various aspects have not been sufficiently established.

Aim

To evaluate, with the use of magnetic resonance imaging (MRI), changes in the area of the pharynx during wakefulness and induced sleep in patients with OSA.

Materials and Methods

A prospective study of thirty-two patients with a polysomnographic diagnosis of OSA. All patients were submitted to MR imaging in order to obtain high-definition anatomical sagittal sequences during wakefulness and during sleep induced with Propofol. An area was defined on the sagittal plane in the midline of the pharynx. This region was called pharyngeal midplane (PMP) area.

Results

A significant difference in PMP area (mm²) was observed between wakefulness and induced sleep in each patient (p < 0.000001).

Conclusion

The patients with OSA suffer a significant reduction of 75,5 % in the area of the pharynx during induced sleep compared to wakefulness.

Radiological airway changes following bipolar radiofrequency volumetric tissue reduction

Objective:

To characterise the appearance of lesions of the tongue base and soft palate induced by bipolar radiofrequency volumetric tissue reduction, using magnetic resonance imaging up to six weeks post-procedure.

Methods:

Five men with sleep-disordered breathing were treated with one session of bipolar radiofrequency volumetric tissue reduction to a number of sites, including the tongue base and soft palate. Magnetic resonance imaging was performed pre-operatively and one week and six weeks after surgery.

Results:

Lesions were visible from day one. T1 (spine lattice relaxation Time)-weighted images demonstrated areas of central hyperintensity, reflecting haemorrhagic, coagulative necrosis, surrounded by hypointensity, representing oedema; corresponding short tau inversion recovery (STIR) sequences showed central hypointensity with surrounding high signal. The lesions expanded up to day three and then gradually diminished, but were still evident at week six on short tau inversion recovery images.

Conclusion:

The characterisation of lesions induced by bipolar radiofrequency volumetric tissue reduction enables us to elucidate the pathophysiology of this procedure, to optimise treatment benefits and clinical outcomes, and to explain patient symptoms.

Avaliação da radiografia cefalométrica lateral como meio de diagnóstico da hipertrofia de adenoide

INTRODUÇÃO: a hipertrofia de adenoide é uma das principais causas da respiração bucal. Entre os métodos utilizados para o diagnóstico dessa condição, os mais precisos são a endoscopia nasal e a ressonância magnética. No entanto, o método mais utilizado, em Odontologia, é a radiografia cefalométrica lateral. OBJETIVO: determinar a eficácia dessa radiografia no diagnóstico da hipertrofia de adenoide, pela sua comparação com a endoscopia nasal. MÉTODOS: foram avaliados 30 indivíduos (7 a 12 anos). Todos fizeram exame de endoscopia nasal e radiografia cefalométrica lateral. Nas endoscopias, foi registrada a porcentagem de obstrução da nasofaringe e, nas radiografias, a menor dimensão anteroposterior livre da nasofaringe. RESULTADOS: os exames se mostraram fortemente correlacionados (r = - 0,793, p-valor < 0,01). Considerou-se portadores de hipertrofia severa de adenoide os pacientes que apresentaram, na endoscopia, obstrução da nasofaringe igual ou superior a 75% e, nas radiografias, o menor diâmetro anteroposterior da nasofaringe igual ou inferior a 5mm; o exame radiográfico teve uma sensibilidade de 75%, especificidade de 86,3%, valor preditivo positivo de 66,7%, valor preditivo negativo de 90,4% e exatidão de 83,3%. CONCLUSÃO: a radiografia cefalométrica lateral se mostrou um exame eficiente para o diagnóstico da hipertrofia de adenoide.

Acute and chronic responses of the upper airway to inspiratory loading in healthy awake humans: an MRI study

We assessed upper airway responses to acute and chronic inspiratory loading. In Experiment I, 11 healthy subjects underwent T(2)-weighted magnetic resonance imaging (MRI) of upper airway dilator muscles (genioglossus and geniohyoid) before and up to 10 min after a single bout of pressure threshold inspiratory muscle training (IMT) at 60% maximal inspiratory mouth pressure (MIP). T(2) values for genioglossus and geniohyoid were increased versus control (p<0.001), suggesting that these airway dilator muscles are activated in response to acute IMT. In Experiment II, nine subjects underwent 2D-Flash sequence MRI of the upper airway during quiet breathing and while performing single inspirations against resistive loads (10%, 30% and 50% MIP); this procedure was repeated after 6 weeks of IMT. Lateral narrowing of the upper airway occurred at all loads, whilst anteroposterior narrowing occurred at the level of the laryngopharynx at loads > or =30% MIP. Changes in upper airway morphology and narrowing after IMT were undetectable using MRI.

[Magnetic resonance imaging in the evaluation of temperature-controlled radiofrequency volumetric tissue reduction]

BACKGROUND

Due to its minimally invasive character, radiofrequency surgery has become a topic of increasing attention, especially with respect to the surgical treatment of sleep-related breathing disorders. Temperature-controlled radiofrequency volumetric tissue reduction is the most common technique employed in these cases. However, despite the increasingly widespread use of this technique, there is little data available on the induced effects in vivo. The aim of the present study was to investigate whether magnetic resonance imaging could be used in the evaluation of the in vivo effects of radiofrequency surgery at the base of the tongue.

PATIENTS AND METHODS

Six patients were treated at the base of tongue with radiofrequency surgery. At 4-6, 8-10 and 24 h after surgery, magnetic resonance imaging was performed using an inversion recovery technique (TIRM) and the lesions created were evaluated.

RESULTS

The lesions could be visualised at all postoperative measurement times. They appeared as oval hypointense structures encircled by a hyperintense area. Lesion size diminished slightly over time.

DISCUSSION

Lesions induced by radiofrequency surgery can be clearly visualised with magnetic resonance imaging. Lesion size may be assessed in relation to energy application. In the future, the treatment of sleep-related breathing disorders may be further optimised with the help of this technique.

Lesion formation in radiofrequency surgery of the tongue base

OBJECTIVES

Temperature controlled radiofrequency volumetric tissue reduction (RFVTR) of the tongue base is a minimally invasive technique for the treatment of obstructive sleep apnea. But despite its widespread use, little is yet known about in vivo effects in humans. Such knowledge would be essential for evidence-based criteria in the selection of energy application.

METHODS

In a preparatory in vitro study, porcine tongues were preserved in growing medium. Lesions with different amounts of energy were applied, and maximum diameters were assessed. In the in vivo study, 11 patients were treated with RFVTR at the tongue base by employing different energy levels (800, 600, 400, or 200 J) on two application sites. Magnetic resonance imagery scans were performed 4 to 6, 8 to 10, and 24 hours after surgery. An inversion recovery technique was used to visualize the lesions.

RESULTS

RFVTR created lesions at the porcine tongue from 50 J and higher. Maximum lesion sizes were achieved with 400 J. In vivo, all the lesions were clearly visible in the postoperative scans. Lesion size increased with the amount of energy applied. Maximum diameters were created from 600 J and higher. Higher amounts of energy only resulted in a slight increase in lesion length.

CONCLUSIONS

The application of 600 J at 85 degrees C leads to optimal lesion sizes. Higher amounts of energy will not lead to a relevant increase in tissue necrosis. With regard to the time needed for application, 600 J appears to be the ideal adjustment for energy delivery in the treatment of the human tongue.