Page 107 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

Distribution of PSMA-ligand in salivary and lacrimal glands on PET/CT
Discussion
The results of this study provide a comprehensive qualitative and quantitative overview of tracer accumulation on PSMA PET/CT in salivary, seromucous, and lacrimal gland tissues in the head and neck. The presented distribution patterns of the major salivary glands are comparable to those (to a lesser extent) reported in studies on different topics using the same tracer [9,10]. In addition, our study illustrates the ability of PSMA PET/CT to visualize minor gland locations, for example in the soft palate, pharyngeal wall, nasal mucosa, and supraglottic larynx. This has not been possible with other imaging modalities previously.
Although Demirci et al. described comparable nasopharyngeal tracer concentration around the fossa of Rosenmüller, in our series this area seemed less well defined and spread over a larger area [10]. Awareness of the physiological tracer distribution in the upper aerodigestive tract mucosal and salivary gland tissues can contribute to a correct diagnostic interpretation of PSMA PET/CT.
Imaging of salivary glands: The saliva-producing acinar cells are distributed over 6 3 paired major and 600-1,000 minor salivary glands, which are organized in
small clusters of mainly mucous cells that are located in the mucosa of the palate,
lips, buccal mucosa, tongue, and floor of the mouth. In addition, there are many
seromucous glands in the oro-, hypo- and nasopharynx, nasal cavities, larynx, trachea, and oesophagus that contain mucous and/or serous cells [7,11]. The nasopharynx, for example, contains 1100-1200 seromucous glands [12]. Anatomic imaging such as CT and MRI generally adequately depicts the parotid and submandibular glands. Therefore, their location, size, and shape are considered common knowledge [4]. The sublingual glands are more difficult to visualize with standard imaging techniques. Until recently, imaging of minor salivary and seromucous glands, located in oral mucosa, lips, tonsils, nasal cavity, nasal sinuses, larynx, trachea, oesophagus, was impossible because of their limited size and poor signal contrast with surrounding tissues; their detection was only possible in case of tumor growth [13]. Today, PSMA PET/CT brings a new technique to clearly depict normal sublingual and minor submucosal gland areas, and to quantify the uptake of the PSMA-ligand as a marker of the presence of glandular cells.
The biomarker PSMA: PSMA was firstly described in 1987 [14]. In 1993, it was successfully cloned and characterized [15]. PSMA is now known as a type 2
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