Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 49, Num. 2, 2003, pp. 177-178

Journal of Postgraduate Medicine, Vol. 49, No. 2, April-June, 2003, pp. 177-178

Images in Radiology

MRI in Sleep Apnoea

Maheshwari PR, Nagar AM, Shah JR,* Patkar DP*

Departments of Radiology, K.E.M Hospital, Parel, Mumbai-400012, and *Dr Balabhai Nanavati Hospital, S. V. Road, Mumbai-400056, India.
Address for Correspondence: Praveen Maheshwari, MD, A-10, Century Staff Quarters, Near TV Center, P. B. Marg, Worli, Mumbai-400025, India. E-mail: praveenparikshitdas@rediffmail.com

Code Number: jp03048

A 37-year-old man with a body mass index of 39 kg/m², presented with hypersomnia during daytime and snoring during sleep. The central nervous system examination and indirect laryngoscopy revealed no abnormality. Polysomnography suggested the diagnosis of obstructive sleep apnoea. Mean arterial oxygen saturation was 89%, while minimum arterial oxygen saturation was 53%. The oxygen desaturation per hour was 20.6. Apnoea-hypopnea index was 17/hour. Subsequently, an MRI of upper airway was performed in awake and asleep state. The pharyngeal airway was imaged in the median sagittal and axial planes using a 0.5T MR. Spin echo T1-weighted images revealed no abnormality (Figure 1). Diazepam (5 mg) was given intravenously and imaging was repeated during the episode of apnoea. The pharyngeal airway became T-shaped due to the collapse of lateral pharyngeal walls (Figure 2). The figure demonstrates narrowing of the lumen to the extent of 70% as compared to dimensions in the wakeful state.

Discussion

Sleep apnoea syndrome (SAS) is characterised by episodes of apnoea that occur for a period of 10 seconds or longer, at least five times per hour during sleep.¹ SAS refers to a clinical disorder that arises from recurrent apnoea during sleep. It has been classified into 3 types: central, obstructive and mixed.² In the central variety, the neural drive to the respiratory muscles is temporarily abolished. In the obstructive variety the respiratory drive in not impaired, but airflow ceases due to the occlusion of the oropharyngeal airway. The mixed variety apnoea consists of central apnoea that is followed by an obstructive component.² The condition is common in males aged between 30-60 years.² The clinical symptoms include history of snoring, daytime hypersomnia and nocturnal choking or gasping.² Obesity and ingestion of alcohol are predisposing factors. In some patients the structural compromise is due to anatomical factors such as micrognathia, retrognathia, adenotonsillar hypertrophy and macroglossia.²

Velopharynx is the most common site of pharyngeal obstruction in these patients. Two factors maintain the patency of the pharyngeal airway in healthy persons even while sleeping: anatomic factor and a functional factor (synchronisation of the activities of the muscles of upper respiratory tract and nerves).³

Polysomnography is the investigation of choice for establishing the diagnosis of SAS and for determining its severity,^2,3 but is a time consuming and expensive test. Because CT scan has high spatial resolution and provides tomographic images, it is often used to diagnose pharyngeal obstruction. However CT provides only axial images and cannot image the entire pharyngeal airway in a single plane.³

MR is a non-invasive modality that allows examination of the entire pharynx in multiple planes and in a short time, with no radiation exposure as compared to CT. It provides good temporal and a high contrast resolution and can evaluate the pharynx on a real time basis.³

Ideally, 1.5T MR, ultra-fast 2D fast low angle shot sequence with 6.5/3.5 [TR/TE], 8 degree flip angle, 300 ms inversion time [TI], 250 mm field of view [FOV], 128X128 matrix and a single excitation.³ is used to obtain mid-sagittal and axial projections during transnasal shallow respiration at rest, simulation of snoring and performance of the Muller's maneuver.⁴

In past, sedation was required for the evaluation of sleep apnoea. Using Muller's manoeuvre has made this requirement obsolete.⁴ The motion of the tongue, soft palate, uvula and posterior pharyngeal surface can be visualised by obtaining 5-6 images per second.⁴ If the pharyngeal cavity is seen to be disappearing in trans-axial and sagittal planes, obstruction is diagnosed. Narrowing is said to be present if the pharyngeal cavity disappears only in one of the images and if there is more than 50% reduction in the pharyngeal space during sleep as compared to maximum area seen in wakeful state.¹ Reduction in airspace up to 50% is considered normal.¹ The sites of obstruction during sleep are identical to those of narrowing during wakefulness in only 31% of cases. In other patients, obstruction occurs only after sleep.³ As the functional factor is different during sleep and wakefulness, imaging should be done in both states.³ MR is the best non-invasive modality for evaluation and follow-up of patients with obstructive sleep apnoea.

References

1. Suto Y, Matsuda E, Inoue Y, Suzuki T, Ohta Y. Sleep Apnea Syndrome. Comparison of MR imaging of the oropharynx with physiologic Indexes. Radiology 1996;201:393-8.
2. Eliot AP. Sleep Apnea. In: Fauci AS, Braunwauld E, Isselbacher KJ, Wilson JD, Martin JB, Kasper DL, et al, eds. Principles of Internal Medicine, 14^th edn. New York: McGraw-Hill; 1998. Vol 2. pp. 1480-3.
3. Suto Y, Matsuo T, Kato T, Hori I, Inoue Y, Ogawa S, et al. Evaluation of the pharyngeal airway in patients with sleep apnea. Value of ultrafast MR imaging. AJR Am J Roentgenol 1993;160:311-4.
4. Jager L, Gunther E, Gauger J, Reiser M. Fluoroscopic MR of the Pharynx in patients with obstructive sleep apnea. AJNR Am J Neuroradiol 1998;19:1205-14.

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