IMAGING TECHNIQUES OF PHARYNX AND LARYNX ARE VERY EASY, WE HERE WILL TRY TO SUMMERIZE THEM.
THANKS TO DR/ DAVID SUTTON MD, FRCP, FRCR, DMRD, FCan.AR (Hon) OUR BELOVED TEACHER
- Lateral Film is the best film projection, as Pharynx and Larynx clear of the cervical spine . as in Fig (1). The Film is placed against the shoulder and the incident beam is centered on :
- Jaw Angle if we want Nasopharynx.
- Thyroid Cartilage If we want Larynx.
Fig. 1 (A) Some of the structures demonstrated on a plain lateral view of the neck. Xerography, although giving an excellent demonstration of the air-soft-tissue interface, is no longer available because of the high radiation dose used. (B) High-kV lateral neck gives an adequate demonstration of the soft tissue anatomy.
- More benefit to opacify lesions below the crico-pharyngeus that cannot be assessed with a laryngeal mirror.
- Tumours of the pharynx will be outlined by barium coating, especially those in the piriform fossae ( difficult to be seen with a mirror).
- The normal larynx will appear as a `filling defect’ in the frontal projection with contrast in the piriform fossa on either side.
- This is well shown on the oblique projection, obtained with the patient swallowing while the head is turned to one side.
- When the larynx fails in its primary function as a protective sphincter for the lungs, ‘spill-over’ will occur to give a `barium laryngogram’.
- This problem is seen more and more in an aging people, who dysphagia is due to mild stroke.
Fig . 2 Lateral View of normal Barium Swallow. The epiglottis (arrow) folds over the larynx as barium passes down into the esophagus .
- It gives a good demonstration of degustation process.
- Passage of the bolus across the back of the tongue with an elevation of the larynx and tilting of the epiglottis down over the closed larynx is shown (Fig. 2).
- Contrast then passes through the open cricopharyngeus into the esophagus.
- Minor functional disorders of swallowing can only be shown by this technique (Fig. 3).
- Videofluoroscopy is an alternative means of assessing swallowing function and a technique for assessment of oral or pharyngeal dysphagia.
Fig.3 Cine barium swallow. Four frames in 1 s, frontal and lateral views. The patient had mild dysphagia due to unilateral vagal paralysis. Various normal and abnormal features are demonstrated. Lateral view. 1. The vallecula fills with barium and is then partially effaced by the normal backward compression of the tongue. 2. The epiglottis is partially immobile and only tilts down to the transverse position, not fully covering the laryngeal inlet. 3. Barium enters the vestibule of the larynx. This may occasionally be observed in asymptomatic subjects but is usually an indication of failure of the laryngeal sphincters ('spill-over'). 4. At the same time the relation of the postphyaryngeal wall to the cervical spine does not change, indicating paralysis of the middle pharyngeal constrictor. 5. Cricopharyngeus contracts and relaxes normally. AP view. 6. The epiglottis shows little movement. 7. The right side of the pharynx contracts normally but the left remains flaccid and filled with barium. 8. Cricopharyngeus contracts and releases normally.
- CT is now the optimum method of imaging the outlines of the nasopharynx but also shows the soft-tissue structures of the infratemporal fossa and parapharyngeal space, which lie alongside the Naso- and oropharynx.
- Formerly this region could be studied radiologically only in an indirect way by examination of surrounding bony structures or by invasive contrast examinations such as sialography and angiography.
- The infratemporal fossa is situated below the skull base and is bounded by the pharyngeal musculature medially and the mandible laterally.
- The most prominent and easily recognized structures within the infratemporal fossa are the pterygoid muscles.The anatomy of this region is depicted in Fig. 4.
- Below, the infratemporal fossa is continuous with the parapharyngeal space.
The role of CT for lesions in this region may be defined as:
• To complement direct examination of lesions in the postnasal space
.• To assess the size and situation and relations of a well-defined
mass for prospective surgical removal, or the extent of local deep infiltration for radiotherapy planning.
• To assess the relation of the mass to the great vessels and the parotid gland: by combining CT with contrast enhancement more accurate differentiation becomes possible.Contrast enhancement should be assessed in the vascular phase by intravenous infusion or bolus injection. Further sections in the coronal plane may give more information. Respiratory movement is less of a problem with the new fast scanners.
- Scanning is begun at the level of the thyroid bone and sequential scans
of 5 min slices are made in a caudal direction.
- The shape of the airway alters as sequential scans are viewed. Above the rounded hypopharynx, it is bisected by the crescentic epiglottis.
- Further down, the median and lateral glossoepiglottic folds delineate the valleculae.
- Below this, the airway assumes a triangular shape and the piriform sinuses are seen as two lateral appendages separated by the aryepiglottic folds.
- At the level of the cords the shape changes to the characteristic glottic chink or boat shape with the sharp anterior commissure extending right up to the thyroid cartilage in the midline (Fig. 5).
- In the subglottic area, there is an even, symmetric oval shape which gives way at the level of the first tracheal ring to an oval flattened posteriorly, which may he likened to the shape of a horseshoe.
- CT provides a non-invasive, quick and effective radiological investigation of the larynx, and is not uncomfortable for the patient.
- It can be done without risk in the face of respiratory obstruction, or after suspected laryngeal injury.
- It gives an accurate assessment of laryngeal anatomy and involvement by tumor, particularly at the glottic level.
- The value of such an assessment is greatly increased if partial laryngectomy is contemplated, but this is an unusual operation in the UK where carcinoma of the larynx is treated with radiotherapy and/or total laryngectomy.
Fig.4 Axial CT of soft tissues below the skull base. (A) Normal section through antra and postnasal space. The arrowheads indicate the openings of the eustachian tubes. m = ramus of mandible; s = styloid process; p = pterygoid muscles. (B) Section at a slightly lower level passes through the soft palate (sp). Tensor and levator palatini blend with the pharyngeal constrictors (c) to give a dense muscle mass. The enlarged but otherwise normal parotid gland has a lower attenuation, i.e. appears darker, than the masseter muscle in front of it but not as dark as the fatty tissue in the parapharyngeal space. Thus the medial limit of the deep parotid lobe can be defined (arrowhead). These features are best shown by MRI.
Fig.5 Axial CT Scan of the normal Larynx at the level of true vocal cords. Note the diamond shape of the airway with the cords in abduction. Contrast is given , so CCA (A) and IJV (I) are shown.
- MRI is superior over CT for neck masses.
- MRI show neck vessels without the need to contrast.
- T1WI gives the best spatial resolution.
- T weighted Protocols give the best view of muscle invasion by carcinoma esp in Tongue base.
- CT with contrast is superior over MRI in the evaluation of Neck Lymph Nodes, however, none of them can differentiate neoplastic from inflammatory hyperplasia, yet metabolic techniques like FDG-PET, SPECT is promising in that.
- Sometimes the presence of Fat can obscure lesions, so fat saturation techniques are very useful, STIR protocol the most dependent one show increase signal intensity from most of the tumors especially Parotid Tumors. But It can’t be used with gadolinium contrast.
- Chemical Shift fat saturation techniques can show recurrent tumor after gadolinium injection.
- Now Fat Saturation Techniques, used with T1 fast spin echo OR Post-gadolinium T protocols are more useful in defining Neck Lesions .
Fig.6 (A) upper image: Sagittal MRI, T 1 -weighted, shows good differentiation between the tongue muscles, the genioglossi in the floor of the mouth and the surrounding fat, especially in the pre-epiglottic space (arrow). (B) lowe image : Sagittal film in a child revealing subglottic stenosis (arrow)
Fig.7 Chordoma. Sagittal MR section, T,-weighted, shows a nonhomogeneous mass in the nasopharynx and replacing the basisphenoid.The tumor has burst out of its capsule and is displacing the brainstem posteriorly.