Page 135 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

Tubarial salivary glands: A potential new organ at risk for radiotherapy
Interpretation of findings
Several factors can explain why these glands have not been noticed previously
as macroscopic gland locations. The occurrence of acinar cell groups in the nasopharynx has been reported, but in a spread out pattern in a large region
instead of localized tissue in an organized clustered glandular structure[3]. The
newly detected tubarial glands involve flat submucosal glandular structures at
a poorly accessible anatomical location under the skull base, an area that can
only be visualized using nasal endoscopy. The macroscopically visible excretory
duct openings may have been noticed, but have not been interpreted as part of
a larger gland. Conventional imaging modalities (ultrasound, CT, MRI) have
never allowed visualization of this submucosal structure and interpretation as a
salivary gland, although an indication of its presence may have been visible in
various prior functional imaging modalities upon retrospective evaluation [16].
Modern multiparametric MRI imaging could only be used to identify the tissue compartment containing the gland, after analyzing the information provided by PSMA-PET/CT and histology. As a result of these coinciding factors, the discovery
depended on the introduction of molecular imaging with radiolabeled PSMA-
ligands. This provided the required high sensitivity and specificity for detection
of salivary gland cells, with a very high contrast-ratio relative to the surrounding PSMA-negative tissues. In combination with 3D anatomical reconstruction of
histological information, this allowed us to realize that these cells in fact form
distinctive macroscopic gland locations. 8
Based on the described anatomical and histological characteristics, and on the demonstrated relation between high-dose RT to the tubarial gland regions and toxicity (xerostomia and dysphagia), we assume the physiological function of the tubarial glands is the moistening and lubrication of the nasopharynx and oropharynx. Although this interpretation of physiology requires confirmation with additional research, it does suggest an opportunity for sparing in RT for patients treated for HNC to avoid toxicity.
One could question whether the tubarial glands should be considered as separate organs, and as major or minor salivary gland locations. However, we think these qualification systems may not be suited and relevant to interpret and appreciate this finding. The accepted definition of an organ is that it consists of more than one kind of tissue, with a definite shape and structure, and performs specific tasks[17].
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