Page 128 - New epidemiological and PSMA-expression based paradigms in salivary gland tumors

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Chapter 8
PET/CT scan is shown in Video 1 in the Supplementary material. Location and extent of the tubarial glands in a random patient. Shown are coronal (B), axial (C) and sagittal (D) slices at the level of the torus tubarius, of PSMA PET projected as yellow signal on grayscale CT. The glandular structure is visible as PSMA-positive tissue (arrows). The coronal slices also show some parts of the parotid and submandibular glands, which demonstrate similar imaging characteristics.
To our knowledge, this structure did not fit prior anatomical descriptions[5,7]. It was hypothesized that it could contain a large number of seromucous acini, with a physiological role for nasopharynx/oropharynx lubrication and swallowing. This could have clinical relevance in oncology, because high-dose external beam radiotherapy (RT) to salivary glands during treatment for head and neck cancer (HNC) or brain metastasis is known to cause damage (toxicity, e.g. interstitial fibrosis, acinar atrophy). This can result in function loss with xerostomia and dysphagia[8,9]. Affected patients experience impaired food intake, digestion, speech problems and increased risk of caries and oral infections, with significant impact on their quality of life[10–12]. The major salivary glands are therefore regarded as organs-at-risk (OAR) and need to be spared when possible. However, since there are no known localized macroscopic glandular structures posterior in the nasopharynx, this area is not included in currently used prediction models for toxicity, nor spared in RT[13,14].
The identification of previously unnoticed salivary gland structures in the posterior nasopharynx could help to explain and avoid radiation-induced side-effects. We performed a comprehensive multi-perspective study with the objective to confirm the presence of this yet unknown glandular entity, and to assess its anatomical and histological characteristics and clinical relevance in RT.
Materials and Methods
Occurrence on molecular imaging
The presence of PSMA-positive tissues in the nasopharynx was evaluated on PSMA PET/CT scans from a retrospective cohort study of 100 consecutively scanned prostate/para-urethral gland cancer patients (from 2017 onwards in NCI and UMCU). Scans were acquired according to routine clinical protocols (Methods 1 in the Supplementary material). The largest cranio-caudal length of the area with uptake was measured on a coronal thick slice and the total tracer uptake in the evaluated region was qualitatively compared with the sublingual glands.