Massimo Magri Clinic Veterinaria Spirano, Spirano (BG), Italy Optimal equipment for ultrasonography of structures of the neck should include a high frequency, 10–12 MHz linear probe and a 6.6 MHz micro-convex probe. These two probes allow visualization with maximal definition of both superficial and deep structures. However, many structures of the neck can be visualized using only a 5–7.5 MHz linear probe typically used for equine obstetrics. Best images are obtained by clipping the hair with a surgical clipper blade and applying coupling gel; however, alcohol will also serve as an adequate contact medium. Ideally, place an examination glove or similar over the probe because continued exposure to coupling gel, particularly alcohol, can cause degradation of the probe and potentially affect image quality and life span of the probe (Figure 25.1). Orientation of the probe must be kept constant over time to obtain comparable images. When scanning in the longitudinal axis (Figure 25.2A), orient the probe so that distal structures are on the left side of the screen and proximal structures are on the right (Figure 25.2B). When scanning in the cross (short) axis (Figure 25.2C), orient the probe so that ventral structures are on the left side of the screen and dorsal structures are on the right (Figure 25.2D). Figure 25.1 Probe protection. Protect the probe from coupling gel or alcohol with an examination glove or similar covering. Figure 25.2 Probe orientation. (A) This image shows orientation of probe for obtaining longitudinal view. (B) Position the probe so the distal aspect of the neck is on the left side of the screen and the proximal aspect is on the right. (C) This image shows orientation of probe for cross-sectional view. (D) Position the probe so the ventral aspect of the neck is on the left side of the screen and the dorsal is on the right. Structures visualized when scanning the neck include major blood vessels (jugular veins and carotid arteries), parotid salivary glands, maxillary salivary glands, guttural pouches, thyroid glands, lymph nodes, esophagus, trachea, and muscle. All structures are bilateral, except for the esophagus, trachea, sternohyoid muscle, and sternothyroid muscle, so suspicious images can be compared to the opposite side assuming a lesion or abnormality is unilateral. For practical reasons we have divided the neck in three scanning regions: upper cervical region, jugular groove, and lateral region. In this region, it is possible to visualize the following structures (Figure 25.3): Figure 25.3 The main ultrasound sites and associated structures in the upper cervical region. This picture illustrates scan sites for images of the parotid gland, guttural pouches, carotid artery, mandibular salivary gland, lymph nodes, and thyroid gland. The main ultrasound landmarks of this region are (Figure 25.4): Figure 25.4 This picture illustrates the main ultrasound landmarks of the upper cervical region. Figure 25.5 Sonogram of the left upper cervical region, cross-sectional view, obtained from a normal adult horse at the level of the temporo-mandibular joint. The parotid salivary gland (1) is visible below the skin and the parotidoauricular muscle, the angle of the stylohyoid bone (2) is clearly visible, casting a strong acoustic shadow. This sonogram was obtained with a wide-bandwidth 4–9 MHz micro-convex linear array transducer, operating at 6.0 MHz, at a display depth of 5 cm. The parotid salivary gland (Figures 25.6, 25.7, 25.8, 25.9, and 25.10) is a well-demarcated, bilateral, multilobulated structure located in the upper cervical region, below the ear, immediately underneath the skin and parotidoauricular muscle. The gland extends from the vertical ramus of the mandible and wing of the atlas cranially to the linguofacial vein distally. Medially, it is adjacent to the guttural pouches and retropharyngeal lymph nodes. The gland has a hyperechoic capsule and septa and a hypoechoic to anechoic parenchyma. It is approximately 2 cm thick and 20 cm long. The salivary duct (Stensen’s duct) is normally not visible with ultrasonography. Abnormalities of the parotid salivary gland are rare, but obstruction of the duct may cause dilation of the salivary duct. In addition, neoplasia, particularly melanomas (Figures 25.08, 25.09, 25.10) may infiltrate this gland. Localized enlargement of unknown origin can be detected as an incidental finding (Figures 25.13 and 25.14). Figure 25.6 Diagram of the localization of parotid salivary gland. Figure 25.7 Parotid salivary gland. This image is a cross-sectional view of the left parotid salivary gland obtained from a normal adult horse. Hypoechoic, multilobulated, structures of the glandular parenchyma (1) are surrounded by hyperechoic capsule and septa. This sonogram was obtained with a wide-bandwidth 10.0 MHz linear array transducer, operating at 12.0 MHz, at a display depth of 5 cm. Figure 25.8 Parotid salivary gland. This picture is of a 9-year-old Criollo gelding with a marked atrophy of the right parotid salivary gland (1) and a prominent ectatic duct (2). Figure 25.9 Parotid salivary gland. (A and B) These sonograms are of the right proximal cervical region obtained from the case in Figure 26.9. The glandular parenchyma (2) is visible only in a very small area. The remaining area of the parotid region is characterized by the presence of the ectatic duct (1) and fibrous tissue that is not homogeneous. A marked acoustic enhancement artifact is present in the far wall of the dilated ducts, confirming that these structures are fluid filled. These sonograms were obtained with a wide-bandwidth 10.0 MHz linear array transducer, operating at 12.0 MHz, at a display depth of 5 cm. Figure 25.10 Parotid salivary gland. These images are (A) cross-sectional and (B) longitudinal views of the right mandibular edge obtained from the case in Figure 26.9. The parotid salivary duct (1) is distended and anechoic. The duct has a tortuous course and a thickened wall. These sonograms were obtained with a wide-bandwidth 10.0 MHz linear array transducer, operating at 12.0 MHz, at a display depth of 5 cm. Figure 25.11 This picture is of a 20-year-old grey horse diagnosed with melanoma. The swelling in the proximal cervical region was irregular, firm, nodular, and not painful. Figure 25.12 Melanoma. This series of sonograms (A), (B), (C), and (D) is of the right proximal cervical region obtained from the case in Figure 26.11. The glandular parenchyma (1) is reduced to a thin layer; beneath it various hyperechoic masses (2) characterized by a variable echogenicity are present. These sonograms were obtained with a wide-bandwidth 10.0 MHz linear array transducer, operating at 12.0 MHz, at a display depth of 5 cm. Figure 25.13 This picture is of a 14-year-old mare that presented with an upper cervical swelling that was, unilateral, firm, nodular, and not painful. Figure 25.14 This sonogram is of the left upper cervical region obtained from the case in Figure 25.13. The glandular parenchyma (1) is normal, except for the presence of a small mass with homogeneous echogenic appearance (2), surrounded by an area of altered glandular parenchyma with dishomogeneous hypoechogenic apperance. These sonograms were obtained with a wide-bandwidth 10.0 MHz linear array transducer, operating at 10.0 MHz, at a display depth of 3.5 cm. The guttural pouches (Figure 25.15) are ventral diverticula of the Eustachian tube and extend from the nasopharynx to the middle ear. They contain air and have a capacity of 300–500 ml in adults. Due to the pouches’ air content, only the walls of the medial and lateral compartments are detectable in the normal horse. However, when an abnormal fluid collection is present, it is visible. The walls of the lateral and medial pouch compartments are readily located. The lateral compartment wall can be seen superiorly, at the level of the tempo-mandibular joint, just below the parotid salivary gland (Figure 25.16). The medial compartment wall can be seen inferior to the common carotid artery, just before the trifurcation (Figures 25.17 and 25.18). A mirror artifact, consequent to the air, can occur and should not be confused with an abnormality. Figure 25.15 Diagram of the localization of guttural pouch and the stylohyoid angle. Figure 25.16 Wall of the lateral compartment of the guttural pouch. This image is a longitudinal view of the left parotid salivary gland (1) and the wall of the lateral compartment of the guttural pouch (2), obtained from a normal adult horse. The hyperechogenic line of the wall of the lateral compartment of the guttural pouch has a reverberation artifact due to the air content of the normal guttural pouch. This sonogram was obtained with a wide-bandwidth 3.0–13.0 MHz linear array transducer, operating at 5.0 MHz, at a display depth of 6.5 cm. Figure 25.17 Wall of the medial compartment of the guttural pouch. This image is a cross-sectional view of the wall of the medial compartment of the guttural pouch (2), just beneath the common carotid artery, a few centimeters caudal to the carotid bifurcation, obtained from a normal adult horse. The hyperechogenic line of the wall of the medial compartment of the guttural pouch has a reverberation artifact due to the air content of the normal guttural pouch. This sonogram was obtained with a wide-bandwidth 4–9 MHz micro-convex linear array transducer, operating at 6.0 MHz, at a display depth of 8 cm. Guttural pouch tympany (Figure 25.19) occurs in young animals, usually less than 1 year of age, when the salpingopharyngeal fold, the flap of tissue covering the pharyngeal opening, fails to let air escape the guttural pouch. With the flap functioning as a one-way valve, the pouch fills with air. Some cases are mild, while others progress to respiratory distress from occlusion of the pharyngeal area from the distended guttural pouch [1] (Figure 25.20). Figure 25.18 Wall of the medial compartment of the guttural pouch. This image is a cross-sectional view of the wall of the medial compartment of the guttural pouch (2), just beneath the common carotid artery (3), a few centimeters caudal to the carotid bifurcation, obtained from a normal adult horse. The hyperechogenic line of the wall of the medial compartment of the guttural pouch can sometimes produce a mirror artifact (4) that reproduce the carotid common artery image distal to the wall of the medial compartment of the guttural pouch. The parotid salivary gland (1) and the mandibular salivary gland (5) are also visible. This sonogram was obtained with a wide-bandwidth 4–9 MHz micro-convex linear array transducer, operating at 6.0 MHz, at a display depth of 5 cm. Figure 25.19 Guttural pouch tympany. This picture is of a 3-month-old Arab Thoroughbred filly with guttural pouch tympany. The foal had marked distension of the throatlatch region, was in respiratory distress, and required an emergency tracheostomy. The percussion exam revealed a tympanic sound in the upper part of the enlargement and a dull sound in the lower part. Figure 25.20 Guttural pouch tympany. Endoscopic examination of a clinical case of guttural pouch tympany. The upper part of the laryngeal area is markedly compressed by the air content of both the guttural pouches, considerably decreasing the airway passage. Guttural pouches may contain exudate or chondroids (inspissated pus) with guttural pouch empyema (Figures 25.21, 25.22, 25.23, and 25.24). Empyema may occur secondary to any respiratory disease, but infection with Streptococcus equi is a common finding. The pouches may contain blood if trauma occurs to any structure associated with the guttural pouch. A common finding in guttural pouch trauma and hemorrhage is fracture of the stylohyoid bone or a lesion at the insertion of the longus capitis and rectus capitis muscles. Another cause of blood in the pouch is guttural pouch mycosis. A fungal plaque forms in the pouch and causes erosion of a blood vessel, usually the internal carotid artery, resulting in hemorrhage into the guttural pouch. Figure 25.21 Guttural pouch tympany. This image is a longitudinal view of the right parotid and laryngeal region. A well-defined distinction between the upper (2) and the lower (1) portion of the right guttural pouch is evident. The upper portion is filled with air (2) that casts a typical reverberation artifact. The lower portion is filled with mucus (1) that has a mildly echogenic, non-homogeneous appearance. This sonogram was obtained with a wide-bandwidth 5.0 MHz linear array, transrectal transducer, operating at 5.0 MHz, at a display depth of 4 cm. Figure 25.22 Guttural pouch empyema. (A) This picture is of a 5-month-old Spanish colt with guttural pouch empyema with an abscess inside the pouch. The foal had marked distension of the throatlatch region and clinical signs of respiratory distress. The mass was firm, not painful, and not adhered to the skin. (B) This image is a cross-sectional view of the right, lateral, laryngeal region. A well demarcated hyperechoic mass (1) is visible deep to the parotid salivary gland (3) and in contact with an enlarged, but architecturally normal, lymph node (2). This mass is inside the guttural pouch which has a visible wall and peripheral layer of hypoechogenic material. This sonogram was obtained with a wide-bandwidth 6.6 MHz micro-convex linear array transducer, operating at 6.6 MHz, at a display depth of 9 cm. Figure 25.23 Guttural pouch empyema. (A) This image is a cross-sectional view of the right lateral laryngeal region obtained from the case in Figure 26.22 after insertion of a Foley catheter and copious lavages of the guttural pouch with a diluted acetylcysteine solution. The echogenic mass (1) is still clearly visible and well defined, but the outer layers are slowly dissolving in the lavage fluid (2). This sonogram was obtained with a wide-bandwidth 6.6 MHz micro-convex linear array transducer, operating at 6.6 MHz, at a display depth of 7 cm. (B) This image is a cross-sectional view of the right lateral laryngeal region obtained from the case in Figure 26.22 after clinical resolution of guttural pouch empyema. The echogenic mass has completely disappeared and the normal structures of the region, the parotid salivary gland (1) and the lymph node (2), are visible. This sonogram was obtained with a wide-bandwidth 6.6 MHz micro-convex linear array transducer, operating at 6.6 MHz, at a display depth of 14 cm. Figure 25.24 (A) (right) and (B) (left): Guttural pouch empyema. These pictures are of an 8-year-old KWPM mare with guttural pouch empyema. The mare had a bilateral purulent discharge from the nostrils. Ultrasound exam has revealed a bilateral empyema of the medial compartment of the guttural pouches (2), with enlarged retropharyngeal lymph nodes (4). Common carotid artery (3), mandibular salivary gland (5), and parotid salivary gland (1) are also visible. This sonogram was obtained with a wide-bandwidth 4–9 MHz micro-convex linear array transducer, operating at 6.0 MHz, at a display depth of 5 cm. The mandibular salivary gland (Figure 25.25) is medial to the parotid salivary gland and lateral to the carotid artery and the guttural pouches; its echogenicity is similar to the parotid salivary gland from which it is divided by an echogenic septum (Figure 25.26). Figure 25.25 Diagram of the localization of the mandibular salivary gland. The carotid artery (Figures 25.27 and 25.28) is an important landmark, particularly at the point where it divides into the external carotid artery, internal carotid artery, and occipital artery. The wall is thicker than that of the jugular vein and the vessel is not compressible.
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Ultrasonography of the Soft Structures of the Neck
Preparation and Scanning Technique
Upper Cervical Region
Parotid Salivary Glands
Guttural Pouches
Mandibular Salivary Glands
Carotid Artery
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