Salivary Gland Imaging






Conventional Plain Films


Conventional X-ray imaging of the salivary gland has diminished relevance. The soft tissue X-ray does not depict a salivary stone well, and the summation effects of conventional X-ray images can make it difficult to locate the few visible structures. The main importance lies in incidental findings of calcifications in the salivary glands. Key examples are X-rays of the cervical spine ( Fig. 3.1.1 ) and dental films ( Fig. 3.1.2 ).




Fig. 3.1.1


X-ray of the cervical spine depicting a huge sialolith in the right submandibular gland.



Fig. 3.1.2


Dental X-ray with an incidental finding of a sialolith in the left submandibular gland.


However, it is sometimes difficult to differentiate salivary stones from other calcifications, including phleboliths or calcified lymph nodes. Additionally, up to 20% of stones cannot be detected by standard X-ray, as they are not radiographically opaque. Other imaging modalities enhance evaluation for stones. Ultrasound is often the next step ( Fig. 3.1.3 ).



Key Point





  • Conventional X-ray imaging of the salivary gland has diminished relevance.





Fig. 3.1.3


Ultrasonography of the left submandibular gland depicting the same stone from Fig. 3.1.2 .





Ultrasound, Ultrasound Guided Fine Needle Aspiration Cytology, and Core Bore Biopsy


Ultrasonography is a noninvasive, relatively inexpensive, real-time examination method, without radiation exposure. It is suitable for the examination of the salivary glands as most relevant aspects are located quite superficially. The reader is also referred to head and neck ultrasound textbooks.


Ultrasound Anatomy


The parotid gland lies partially superior to the masseter muscle and in between the retromandibular space, anterior to the mastoid ( Fig. 3.2.1 ). Stensen’s duct navigates around the masseter muscle, perforates the buccinator muscle, and enters the oral cavity. It normally is not visible on ultrasound; however, this often can be achieved by administering the patient a sialagogue ( Fig. 3.2.2 ). Obstructions, including stones or stenosis, can dilate the duct. Sometimes an accessory gland can be found next to the duct. It can be difficult or even impossible to visualize the complete deep lobe of the gland by ultrasound. Penetration of the ultrasound waves is limited due to tissue attenuation and the shadow of the mandible that prevent visualization of parts lying in the deep parotid lobe.




Fig. 3.2.1


Ultrasound anatomy of the parotid gland: the retromandibular vein (rv) is often at the depth of the facial nerve and therefore divides the deep from the superficial lobe. The temporal artery (ta) lies even deeper than the vein. mm, masseter muscle; ln, lymph node.



Fig. 3.2.2


Stensen’s duct is normally not visible by ultrasound. However, provocation of salivary production by use of a sialagogue (e.g., ascorbic acid) can dilate the Stensen’s duct (sd, v arrowheads). Deep to the duct, the masseter muscle is visible.


The submandibular gland is situated in the submandibular triangle, formed by the body of the mandible, and the anterior and posterior bellies of the digastric muscle. The mylohyoid muscle often indents the gland near to the hilum of the gland. When examining the gland by ultrasound, it is often possible to visualize the tongue and the pharyngeal tonsil at the same time ( Fig. 3.2.3 ). The mandible is in close proximity to the submandibular gland ( Fig. 3.2.4 ). The facial artery and vein cross the gland. The visualization of Wharton’s duct is also possible by provocation with a sialagogue.




Fig. 3.2.3


The submandibular gland (gsm) can often be visualized together with the tongue (lingua) and pharyngeal tonsil (to).



Fig. 3.2.4


The transverse view of the submandibular gland (gsm) also shows the close relationship with the mandible. mmh, mylohyoid muscle, lingua (tongue).


The sublingual gland in the longitudinal view is positioned above the mylohyoid muscle behind the front part of the mandible, lateral to muscles of the tongue ( Fig. 3.2.5 ). Both sublingual glands and associated muscles can be visualized on transverse view ( Fig. 3.2.6 ). The duct system of the sublingual gland is normally not visible. However, it has a close relationship to Wharton’s duct, which runs superficially. When Wharton’s duct is dilated by an obstruction from a stone, this relationship can become visible ( Fig. 3.2.7 ).




Fig. 3.2.5


The longitudinal view of the sublingual gland (gsl) shows its close relationship to the mandible, the tongue (lingua), and the mylohyoid muscle (mmh). md v ant, anterior belly of the digastric muscle.



Fig. 3.2.6


The transverse view of the floor of the mouth includes the sublingual gland (gsl); the mylohyoid muscle (mmh); the anterior belly of the digastric muscle (mdg); the genioglossal muscle (mgg); the geniohyoid muscle (mgh); and the tongue (lingua). Sometimes even in front, accessory parts of the submandibular gland (gsm) can be found.



Fig. 3.2.7


A stone obstructs Wharton’s duct (wd) of the right submandibular gland (gsm). The dilated duct is in direct contact with the sublingual gland (the gray area on the image above the duct, just left and above the stone). Note the different echogenity of the sublingual gland (normal echotexture for a salivary gland, similar to the thyroid gland) and of the swollen submandibular gland (less echogenity). An acute infection of the gland can lead to a similar loss of echogenity due to edematous swelling.


Inflammatory Diseases


An acute viral or bacterial infection leads to a swollen gland with a hypoechoic texture (see Fig. 3.2.7 ). In a bacterial infection, the duct system may become visible due to thickened secretion. In contrast, the ultrasonographic appearance of a chronic inflammatory process (e.g., Sjögren syndrome or chronic recurrent juvenile parotitis) is characterized by multiple hypoechoic lesions within the gland ( Fig. 3.2.8 ).




Fig. 3.2.8


The ultrasound of this parotid gland (pg) shows signs of a chronic inflammatory process with multiple hypoechoic lesions. This pattern can be seen in Sjögren syndrome or in chronic recurrent juvenile parotitis. In this case it was the latter one.


Neoplasms


Many types of benign and malignant neoplasms can be found in the salivary glands. The most frequent benign neoplasms of the parotid salivary glands are pleomorphic adenoma and Warthin tumor.


A Warthin tumor (papillary cystadenoma lymphomatosum) is a benign lesion which not infrequently can be found in both parotid glands or as multiple lesions in one gland. They appear as oval, hypoechoic, partially anechoic, well-circumscribed lesions ( Fig. 3.2.9A ). Due to their low echogenicity they show distal acoustic enhancement and they can sometimes present with hypervascularity on ultrasound ( Fig. 3.2.9B ). It can be difficult to distinguish a Warthin tumor from a cyst, a lymph node, or other benign neoplasms such as a pleomorphic adenoma.




Fig. 3.2.9


A Warthin tumor in the right parotid gland. (A) The tumor is hypoechoic and well-circumscribed. Note the distal acoustic enhancement. (B) With color Doppler (duplex mode), hypervascularization can infrequently be observed. In this case it made it difficult to distinguish the tumor from a lymph node as the vascularization in this case mimics a lymph node hilum. pg, parotid gland; retrom v, retromandibular vein; ta, temporal artery.


Pleomorphic adenomas are also hypoechoic with well-defined borders, with distal enhancement. They often can be differentiated from a Warthin tumor by a lobulated or polycyclic appearance ( Fig. 3.2.10 ). Their echotexture can be homogenous, inhomogeneous, or even with calcifications. Vascularity is usually poor on color Doppler; however, the pseudo-capsule can contain several vessels.




Fig. 3.2.10


Pleomorphic adenoma of the right parotid gland (pg): the lesion is hypoechoic with a distal echo enhancement. It frequently presents with lobulated but well-defined borders.


A multitude of other benign tumors exist. Vascular lesions can show increased vascularity on color Doppler and calcified-like phleboliths. Lipomas are hypoechoic with multiple hyperechoic linear structures regularly distributed within the lesions. Other benign tumors (e.g., oncocytomas, schwannomas) mostly do not have any specific or distinctive features on ultrasound examination.


The characteristics of malignant tumors can vary. They are often characterized by irregular shapes and borders, heterogeneity, often hypoechogenicity, and locoregional metastasis ( Fig. 3.2.11 and ). However, their appearance can mimic benign tumors. The histologic types of malignant tumors do not have any pathognomonic sign on ultrasound.




Fig. 3.2.11


Malignant tumor of the right parotid gland (pg): the larger lesion above the mandible is inhomogenous, mostly hypoechoic, has blurred margins, and cannot be differentiated from the masseter muscle (mm) above the mandible. On the left side a local metastasis can be seen (smaller lesion). The histology of the lesion was an adenocarcinoma.


Minimally Invasive Tissue Acquisition in Salivary Gland Lesions With Ultrasound Guidance


Both fine needle aspiration cytology (FNAC) and core bore biopsies (CBB) can be performed under sonographic control. The diameter of the needles for CBB is usually larger than for FNA. The risk for complications including bleeding and cell seeding is likely correlating with the diameter of the needle utilized. The amount of tissue harvested also correlates with the diameter. Multiple systems exist ( Fig. 3.2.12 ). The right setting is important: the patient and the area of interest should be situated between the examiner and the ultrasound screen, so that the examiner can view and work in the same direction without having to turn around ( Fig. 3.2.13 ). There are principally two techniques used: the “long axis” and “short axis” techniques. In the long axis technique (also shown in Fig. 3.2.13 ) the needle is advanced along the plane of the ultrasound beam (parallel technique). The movement of the needle tip can be visualized for most of the technique. This gives good control and can reduce the risk of traumatizing adjacent structures. However, adjacent structures are often not visualized using the long axis technique. Adjacent structures are more readily visualized for the short axis technique. Here the needle is not advanced within the plane of the ultrasound beam but usually is first visualized when the needle tip strikes the plane of the target lesion. The needle is seldom exactly perpendicular to the plane; however, some authors refer to the technique as a “perpendicular technique.” Sometimes anatomy and space available do not allow the use of the parallel long axis technique.




Fig. 3.2.12


Various biopsy devices exist. The devices on the images are (from left to right): (1) Chiba biopsy needle, 23 G × 5 cm, with “echotip” (a roughened surface near the tip for better echogenity), Cook Inc., Bloomington, IN, USA. (2) Quick core biopsy needle, 20 G × 15 cm, Cook Inc. (3) Temno biopsy system, 20 G × 6 cm, Merit Medical Systems, Inc., South Jordan, Utah, USA. (4) BioPince, full core biopsy instrument, 18 G × 10 cm, Argon Medical Devices Inc., Athens, TX, USA. (5) Tru-Cut biopsy device, 18 G × 24 cm, Merit Medical Systems, Inc. (6) Spirotome, soft tissue biopsy needle set, outer needle (right side around the trocar): 8 G × 15 cm; inner needle with spiral cutting tip (left side): 10 G × 22 cm, Cook Inc. (7) Biopsie handy, 18 G × 10 cm, SOMATEX Medical Technologies GmbH, Teltow, Germany. Optional port systems are offered by some manufacturers (e.g., coaxial introducer systems). They allow obtaining multiple tissue samples through a single insertion site. (A) Overview of the devices. (B) Tips of the devices.



Fig. 3.2.13


Setting for interventional ultrasound: the area of interest of the patient is situated between the examiner and the ultrasound screen. The direction of view and manipulation are the same and the examiner does not have to turn around. The plane of the ultrasound and the direction of the needle are parallel (“long axis” technique). A handle for aspiration is used.


and show the parallel technique. The target structure is visualized and the trajectory for the instrument planned. The ultrasound transducer and instrument are aligned so that the instrument will advance in the plane of the ultrasound beam. The instrument should be inserted with some distance to the transducer. Otherwise, the instrument might not go deep enough, or damage the transducer. While advancing the instrument, it might be necessary to correct the ultrasound head position to visualize the target and the instrument at the same time. Especially the tip of the instrument should be seen to avoid trauma to surrounding structures. In the event that it is not possible to reach the target using the initiated path, it is advisable to pull the instrument back and start with a new direction instead of trying to bend the instrument. shows an FNAC of a pleomorphic adenoma depicted in Fig. 3.2.10 . is a record of a CBB of the adenocarcinoma shown in Fig. 3.2.11 and in .


Feb 24, 2020 | Posted by in OTOLARYNGOLOGY | Comments Off on Salivary Gland Imaging

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