A

Figure 2.23. CT (a) and PET (b) images in axial plane demonstrating normal submandibular (long thin arrow) and sublingual gland (medium arrow) activity. Note the abnormal uptake higher than and anterior to the submandibular glands (short fat arrow). Metastatic lymphadenopathy was diagnosed at the time of surgery.

Figure 2.22. CT (a) and PET (b) images in axial plane demonstrating normal parotid gland activity (arrow).

does not influence FDG imaging (Stahl et al. 2002). SUV of greater then 2.5 has become a threshold for abnormal or neoplastic uptake (originally described by Patz et al.) (Patz, Lowe, and Hoffman et al. 1993; Wang et al. 2007). However, careful analysis must be undertaken when evaluating lesions based on SUVs, as there is a significant

Figure 2.23. CT (a) and PET (b) images in axial plane demonstrating normal submandibular (long thin arrow) and sublingual gland (medium arrow) activity. Note the abnormal uptake higher than and anterior to the submandibular glands (short fat arrow). Metastatic lymphadenopathy was diagnosed at the time of surgery.

overlap of SUVs for malignant and benign tumors and inflammatory conditions. One cannot depend on SUV measurements alone and must take into consideration clinical data as well as radiologic imaging findings.

Table 2.3. SUV of salivary glands.

Gland SUV Max SUV Mean SUV Mean

Submandibular 0.56-5.14 2.22 ± 0.77 2.11 ± 0.57 gland

Sublingual 0.93-5.91 4.06 ± 1.76 2.93 ± 1.39 gland

(b) Nakamoto, Tatsumi, and Hammoud et al. 2005. SD = standard deviation.

POSITRON EMISSION TOMOGRAPHY/ COMPUTED TOMOGRAPHY (PET/CT)

Head and neck imaging has greatly benefited from the use of FDG PET imaging for the staging, restag-ing, and follow-up of neoplasms. The recent introduction of PET/CT has dramatically changed the imaging of diseases of the head and neck by directly combining anatomic and functional imaging.

The evaluation of the head and neck with FDG PET/CT has been significantly and positively affected with detection and demonstration of the extent of primary disease, lymphadenopathy, and scar versus recurrent or residual disease, pre-surgi-cal staging, pre-radiosurgery planning, and follow-up post-therapy.

The role of FDG PET or PET/CT and that of conventional CT and MRI on the diagnosis, staging, restaging, and follow-up post-therapy of salivary gland tumors have been studied (Bui, Ching, and Carlos et al. 2003; de Ru, Van Leeuwen, and Van Benthem et al. 2007; Keyes, Harkness, and Greven et al. 1994; Otsuka et al. 2005; Roh, Ryu, and Choi et al. 2007). Although both CT and MRI are relatively equal in anatomic localization of disease and the effect of the tumors on local invasion and cervical nodal metastases, FDG PET/CT significantly improved sensitivity and specificity for salivary malignancies including nodal metastases (de Ru, Van Leeuwen, and Van Benthem et al. 2007; Jeong, Chung, and Son et al. 2007; Otsuka et al. 2005; Roh, Ryu, and Choi et al. 2007; Uchida, Minoshima, and Kawata et al. 2005).

Early studies have demonstrated FDG PET's relative inability to distinguish benign from malignant salivary neoplasms (Keyes, Harkness, and Greven et al. 1994). The variable uptake of FDG

by pleomorphic adenomas and the increased uptake and SUVs by Warthin's tumor result in significant false positives (Jeong, Chung, and Son et al. 2007; Roh, Ryu, and Choi et al. 2007). In a similar manner, adenoid cystic carcinomas, which are relatively slower growing, may not accumulate significant concentrations of FDG and demonstrate low SUVs and therefore contribute to the false negatives (Jeong, Chung, and Son et al. 2007; Keyes, Harkness, and Greven et al. 1994). False negatives may also be caused by the relatively lower mean SUV of salivary tumors (SUV 3.8 ± 2.1) relative to squamous cell carcinoma (SUV 7.5 ± 3.4)(Roh, Ryu, and Choi et al. 2007). The low SUV of salivary neoplasms may also be obscured by the normal uptake of FDG by salivary glands (Roh, Ryu, and Choi et al. 2007). In general, FDG PET has demonstrated that lower grade malignancies tend to have lower SUV and vice versa for higher grade malignancies (Jeong, Chung, and Son et al. 2007; Roh, Ryu, and Choi et al. 2007). FDG PET has been shown to be more sensitive and specific compared to conventional CT or MRI (Cermik, Mavi, and Acikgoz et al. 2007; Otsuka et al. 2005; Roh, Ryu, and Choi et al. 2007). Small tumor size can contribute to false negative results and inflammatory changes contribute to false positive results (Roh, Ryu, and Choi et al. 2007). The use of concurrent salivary scintigraphy with 99mTc-pertechnetate imaging can improve the false positive rate by identifying Warthin's tumors and oncocytomas, which tend to accumulate pertech-netate (and retain it after induced salivary gland washout) and have increased uptake of FDG (Uchida, Minoshima, and Kawata et al. 2005).

Diagnostic Imaging Anatomy

PAROTID GLAND

The average adult parotid gland measures 3.4 cm in AP, 3.7 cm in LR, and 5.8 cm in SI dimensions and is the largest salivary gland. The parotid gland is positioned high in the suprahyoid neck directly inferior to the external auditory canal (EAC) and wedged between the posterior border of the mandible and anterior border of the styloid process, sternocleidomastoid muscle, and posterior belly of the digastric muscle (Figures 2.24 through 2.30; also see figures 2.17 through 2.19). This position, as well as the seventh cranial nerve, which traverses the gland, divides the gland functionally

Figure 2.24. Axial CT of the neck demonstrates the intermediate to low density of the parotid gland.

Figure 2.25. Reformatted coronal CT of the neck at the level of the parotid gland demonstrating its relationship to adjacent structures. Note the distinct soft tissue anatomy below the skull base.

Figure 2.26. Reformatted sagittal CT of the neck at the level of the parotid gland demonstrating its relationship to adjacent structures including the external auditory canal. Note the slightly denser soft tissue density in the parotid tail, the so-called "earring lesion" of the parotid gland. Cervical lymphadenopathy (arrow) was diagnosed at surgery.

Figure 2.25. Reformatted coronal CT of the neck at the level of the parotid gland demonstrating its relationship to adjacent structures. Note the distinct soft tissue anatomy below the skull base.

Figure 2.26. Reformatted sagittal CT of the neck at the level of the parotid gland demonstrating its relationship to adjacent structures including the external auditory canal. Note the slightly denser soft tissue density in the parotid tail, the so-called "earring lesion" of the parotid gland. Cervical lymphadenopathy (arrow) was diagnosed at surgery.

(not anatomically) into superficial and deep "lobes." Its inferior extent is to the level of the angle of the mandible, where its "tail" is interposed between the platysma superficially and the sternocleidomastoid muscle (SCM) deep to the tail of the parotid. The parotid gland is surrounded by the superficial layer of the deep cervical fascia. The parotid space is bordered medially by the parapha-ryngeal space (PPS), the carotid space (CS), and the posterior belly of the digastric muscle. The anterior border is made up of the angle and ramus of the mandible along with the masticator space (MS). The posterior border is made up of the styloid and mastoid processes and the SCM. The gland traverses the stylomandibular tunnel, which

JPEG 12 AmiJ3=90 05.06:1

Figure 2.27. Axial T1 MRI image at the level of the parotid gland demonstrating the slightly higher signal as compared to skeletal muscle but less than subcutaneous fat.

MffilMOnH 1

Figure 2.27. Axial T1 MRI image at the level of the parotid gland demonstrating the slightly higher signal as compared to skeletal muscle but less than subcutaneous fat.

Figure 2.29. Sagittal fat suppressed T1 MRI image of the parotid gland demonstrating mild enhancement and lack of subcutaneous fat signal in the upper neck but incomplete fat suppression at the base of the neck.

Figure 2.28. Coronal STIR MRI image at the level of the parotid gland demonstrating the nulling of the subcutaneous fat signal on STIR images and low signal from the partially fatty parotid gland.

is formed by the posterior border of the mandibular ramus, the anterior border of the sternocleido-mastoid muscle, the anterior border of the stylomandibular ligament, and the anterior border of the posterior belly of the digastric muscle and the skull base on its superior aspect (Beale and Madani 2006; Som and Curtin 1996). The external carotid artery (ECA) and retromandibular vein (RMV) traverse the gland in a craniocaudal direction, posterior to the posterior border of the mandibular ramus. The seventh cranial nerve (CN 7) traverses the gland in the slightly oblique antero-posterior direction from the stylomastoid foramen to the anterior border of the gland passing just lateral to the RMV. The seventh cranial nerve divides into five branches (temporal, zygomatic, buccal, mandibular, and cervical) within the substance of the gland. Prior to entering the substance of the parotid gland, the facial nerve gives off small branches, the posterior auricular, posterior digastric, and the stylohyoid nerves. The intraparotid facial nerve and duct can be demonstrated by MRI using surface coils and high-resolution acquisition (Takahashi et al. 2005). Because the parotid gland encapsulates later in development than other salivary glands, lymph nodes become incorporated a

terminate in the oral mucosa lateral to the maxillary second molar. Fifteen to 20% of the general population also has an accessory parotid gland that lies along the surface of the masseter muscle in the path of the parotid duct.

In the pediatric population, the parotid gland is isodense to skeletal muscle by CT and becomes progressively but variably fatty replaced with aging. Therefore the CT density will progressively decrease over time (Drumond 1995). By MRI the parotid gland is isointense to skeletal muscle on T1 and T2 weighted images, but with progressive fatty replacement demonstrates progressive increase in signal (brighter) similar to but remaining less than subcutaneous fat. Administration of iodinated contrast for CT results in slight enhancement (increase in density and therefore brightness). Administration of intravenous gadolinium (Gd) contrast results in an increase in signal (T1 shortening) and therefore brightness on MRI scans. By US the acoustic signature is isoechoic to muscle, but with fatty replacement becomes hyperechoic (more heterogenous grey). Therefore, masses tend to stand out as less echogenic foci. Normal uptake on FDG PET varies but is mild to moderate relative to muscle and decreases over age.

Was this article helpful?

0 0
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment