Abstract
Objectives
This study aimed to examine the diffusion properties, signal characteristics and size of the parotid and submandibular gland in neck magnetic resonance (MR) imaging.
Methods
In the study, neck MRI images of 80 patients, 40 men and 40 women, were examined. Area and “Apparent Diffusion Coefficient (ADC)” measurements of bilateral parotid and submandibular glands were measured in MRI images. The findings were compared between genders and between two age groups: 18-50 years and 51-80 years.
Results
Left submandibular area measurements in men (394.4±107.1 mm2) were found to be statistically significantly larger than in women (330.1±89.8 mm2) (p<0.05). A significant difference was detected in right and left submandibular and parotid gland heterogeneity degrees according to the age groups of the patients (p<0.05). While grade 0 and grade 1 were more common in the 18-50 age groups, grade 1 and grade 2 were more common in the 51-80 age groups. In each area; and ADC measurements of the parotid glands; and submandibular glands bilaterally, there were positive correlations (p<0.05). However, there were negative correlations between ADC and area measurements in parotid glands (p<0.05).
Conclusion
As a result, it was observed that the heterogeneity in the gland increased as the age of the patients increased. Neck MRI is frequently used today in the diagnosis of salivary gland diseases, and it is thought that heterogeneity in the salivary gland with age may be helpful in the diagnostic steps in MRI.
Introduction
Salivary gland disorders encompass a broad spectrum of conditions, including inflammatory, infectious, autoimmune, and neoplastic diseases, as well as structural alterations induced by treatments such as radiotherapy (RT). 1 Diagnosing conditions of the major salivary glands through imaging can be challenging due to overlapping radiological features among different gland abnormalities.
Magnetic resonance imaging (MRI) is the preferred imaging modality for evaluating soft tissue contrast, inflammation, destruction, and the spread of lesions in the salivary glands. 2 Recently, diffusion-weighted imaging (DWI) has become an integral part of head and neck MRI protocols because it provides valuable information regarding tissue cellularity and physiological processes without the need for intravenous contrast.3,4 DWI evaluates the random microscopic motion of water molecules within tissues. In highly cellular environments (such as malignant tumors) or when the Na-K pump is impaired, the extracellular space narrows, leading to restricted water diffusion, which presents as a low Apparent Diffusion Coefficient (ADC) value.5-7 For instance, diffusion restriction in the parotid gland is widely used as a predictor of malignancy, with ADC values for malignant tumors typically ranging between 0.9-1.3 x 10-3 mm2/s, whereas values greater than 1.8 x 10-3 mm2/s are highly predictive of benign entities like pleomorphic adenomas.8-13
Despite the extensive use of DWI in diagnosing salivary gland tumors, there is a notable gap in the literature regarding the baseline physiological, age-related, and gender-related variations in the major salivary glands of healthy individuals. To accurately utilize MRI for diagnostic purposes, normal physiological changes—such as age-related fatty infiltration—must first be well defined. Therefore, the present study aimed to examine the normal diffusion properties (ADC), heterogeneity characteristics, and cross-sectional areas of the parotid and submandibular glands in adults without salivary gland pathology, and to evaluate how these parameters change with age and gender.
Materials and Methods
This retrospective study was carried out at Kırıkkale University, within the Otorhinolaryngology and Radiology Departments of the Faculty of Medicine, following the guidelines set in the Declaration of Helsinki. Neck MRI scans were accessed from the Radiology Department’s database at Kırıkkale University, Faculty of Medicine. Approval from the Non-Interventional Research Ethics Committee of Kırıkkale University was granted on 07.10.2021, under the reference number 2021/14.
The data of this study was retrieved from the Specialization Thesis of the first author. 14
Patients
This retrospective study evaluated the neck MRI scans of patients over 18 years old who presented to the Otorhinolaryngology outpatient clinic between January 2015 and July 2023. They had a neck diffusion magnetic resonance (MR) imaging examination recorded in the “Picture Archiving and Communication Systems (PACS)” interface for various reasons, and who had a salivary gland in their MR images.
To prevent selection bias and ensure the study population reflected normal physiological conditions, strict inclusion and exclusion criteria were applied. Patients who underwent neck MRI for reasons unrelated to salivary gland pathology (e.g., evaluation of cervical lymphadenopathy, neck pain, or dysphagia) but had completely normal major salivary glands radiologically and had no signs of neoplasm were included.
Patients with the following conditions were strictly excluded: any focal mass, neoplasm, or sialolithiasis in the salivary glands; a history of Sjögren’s syndrome, diabetes mellitus, or other systemic/autoimmune inflammatory diseases; prior head and neck radiotherapy; the use of medications known to affect salivary gland function (e.g., anticholinergics); and images with significant artifacts preventing optimal evaluation.
A total of 80 patients were included. To evaluate the impact of age, age was analyzed as a continuous variable, but patients were also categorized into two physiological groups: younger adults (18-50 years, n=31) and older adults (51-80 years, n=49). The cohort consisted of 40 men and 40 women.
Radiological Measurements
The MRI examinations used in the study were obtained with a 1.5 Tesla MRI device (Intera Master, Philips Medical Systems, Cleveland, USA) using a standard neck coil. MRI examinations; T1-weighted, T2-weighted and fat-suppressed images were obtained on the axial plan, and T1 and T2-weighted images were obtained on the sagittal plane, with a section interval of 3 mm and an “intersection gap” of 1 mm. Based on the images obtained, staging is performed according to the ratio between the area covered by the fat within the parenchyma and the entire parenchymal area. In addition, area measurements from the widest points of the parenchyma in the axial plane and 3-plane dimension measurements were made and recorded.
EPI sequence was used for diffusion-weighted MR images. Images TR msec/TE mn; It was obtained in the axial plane with the parameters 3942/92, deviation angle 90°, FOV 230x220 mm, matrix 128x90 mm, section thickness 5 mm, “interslice gap” 1 mm. First, T2-weighted images were obtained without applying a diffusion gradient (b=0mm
2
/sec). Then, diffusion-sensitive gradients were applied in 3 directions (x, y, z axes) using the value b=1000 mm2/sec. “Trace” images were obtained by averaging three gradients. ADC maps were created from these images and the evaluation was completed by measuring the parotid and submandibular gland parenchyma from more than one level. In each evaluation, average ADC values were calculated by measuring the “Region of Interest (ROI)” from three different points in the parenchyma. The average ROI size used was determined as 20±1 mm. All measurements were made separately on the right and left sides of each patient (Figures 1 and 2). Then, on T1-weighted axial MR images, area measurements were made at the widest points in optimal sections where the submandibular gland and parotid gland were best selected. All measurements were made bilaterally, on the right and left sides separately (Figures 3 and 4). Parotid Gland ADC Measurement. The measurements were performed on axial T1-weighted neck MRI sections. (Note: The term “Alan” displayed on the image interface is the Turkish translation for “Area”) Submandibular Gland ADC Measurement. The measurements were performed on axial T1 weighted neck MRI sections. (Note: The term “Alan” displayed on the image interface is the Turkish translation for “Area”) Parotid Gland Area Measurement. The measurements were performed on axial T1-weighted neck MRI sections. (Note: The term “Alan” displayed on the image interface is the Turkish translation for “Area”) Submandibular Gland Area Measurement. The measurements were performed on axial T1 weighted neck MRI sections. (Note: The term “Alan” displayed on the image interface is the Turkish translation for “Area”)
Additionally, to assess parenchymal architecture, the heterogeneity of the parotid and submandibular glands was graded on a standardized 5-point ordinal scale as follows
15
: • Grade 0: Definitely normal (homogeneous) • Grade 1: Probably normal (almost homogeneous) • Grade 2: Probably abnormal (slightly heterogeneous) • Grade 3: Clearly abnormal (moderately heterogeneous) • Grade 4: Definitely abnormal (severely heterogeneous)
Statistical Analysis
The patient data gathered for the study were analyzed using IBM’s SPSS for MacOS 29.0 (IBM Corp., Armonk, NY). Descriptive statistics for categorical variables were expressed as frequencies and percentages, while continuous variables were summarized with mean, standard deviation, median, and range (minimum and maximum). The Kolmogorov-Smirnov test was applied to assess the normality of the variables. To compare groups, the Independent Samples t-test was used for normally distributed variables between two groups, the Mann-Whitney U test for non-normally distributed variables, and the Chi-Square test for categorical data. The Spearman’s rho correlation test was employed to explore the relationship between continuous variables. Statistical significance was set at a p-value of less than 0.05.
Results
Distribution of Demographic and Clinical Findings of the Patients
Overall, the mean cross-sectional area of the right parotid gland was 924.1±188.9 mm2, and the left was 917.1±183.8 mm2. The mean ADC value was 1.016±0.162 x10-3 mm2/s for the right parotid and 1.021±0.168 x10-3 mm2/s for the left parotid. For the submandibular glands, the mean area was 362.4±94.5 mm2 on the right and similar on the left. The mean ADC was 1.036±0.150 x10-3 mm2/s for the right submandibular and 1.046±0.151 x10-3 mm2/s for the left submandibular gland (Table 1).
Gender Comparisons
Distribution of the Parotid and Submandibular Gland Area and Diffusion Measurements of Patients by Gender
*Independent Samples t test.
†Mann-Whitney U test.
‡Chi-square test, p<0.05.
The distribution of right and left submandibular salivary gland area, grade and diffusion measurements according to the gender of the patients is shown in Table 2. When the table is examined; While there was a statistically significant difference in the left submandibular area measurement according to the gender of the patients, the measurements of men were found to be higher than women (p<0.05). No statistically significant differences were observed between gender groups in other measurements.
Age Group Comparisons
Distribution of Patients’ Parotid and Submandibular Gland Measurements According to Age Groups
*Independent Samples t test.
†Mann-Whitney U test.
‡Chi-square test.
Correlation Analysis
Correlation Tests Between Patients’ Age and Parotid and Submandibular Gland Measurements (n=80)
Discussion
MRI provides excellent soft-tissue contrast and high spatial resolution without the use of ionizing radiation, making it the superior modality for evaluating the major salivary glands and deep neck spaces.16,17 While DWI is proven to be effective in differentiating benign from malignant salivary gland lesions, the interpretation of these sequences relies heavily on understanding the baseline physiological appearance of these glands. 18
As a widely used non-invasive functional imaging technique, diffusion-weighted imaging (DWI) assesses the random movement of water molecules, providing valuable insight into tissue cellularity. 19 While the apparent diffusion coefficient (ADC) is widely recognized as a reliable biomarker for characterizing and differentiating parotid gland tumors,6,20 its standard calculation presents certain limitations. Specifically, traditional mono-exponential DWI models often yield artificially inflated ADC values due to the confounding effects of capillary perfusion, preventing an exact representation of true water diffusion at the molecular level. 21
This study provides valuable normative data by evaluating the area, heterogeneity, and ADC values of parotid and submandibular glands in an adult population free of salivary gland pathology.
In submandibular gland ADC measurements, when we look at the distribution of submandibular gland measurements according to the gender of the patients, it was found that the left submandibular area measurements in men (394.4±107.1 mm2) were statistically significantly larger than in women (330.1±89.8 mm2) (p<0.05). A statistically significant relationship was observed in the degree of right and left submandibular and parotid gland according to the age groups of the patients (p<0.05). While grade 0 and grade 1 are more common in the 18-50 age group, grade 1 and grade 2 are more common in the 51-80 age group. In area and ADC measurements in the entire patient group (right and left side) and age groups (18-50 and 51-80 years), no statistically significant difference was detected between the groups in parotid gland measurements, area and ADC measurements and grade evaluation according to gender (p>0.05).
In each area; and ADC measurements on both sides of the parotid glands; and submandibular glands, there were positive correlations (p<0.05). However, there were negative correlations between ADC and area measurements in parotid glands (p<0.05). It can be said that as the area of the parotid gland decreased, the ADC values increased. In our study, our patients were examined with diffusion-weighted neck MRI, but patients with salivary gland masses were not included in our study.
Our most notable findings relate to the effects of aging on the salivary glands. We observed that glandular heterogeneity significantly increases with age in both the parotid and submandibular glands. Furthermore, a significant negative correlation was found between the cross-sectional area and ADC values in the parotid glands—meaning that smaller parotid glands exhibited higher water diffusion (ADC).
These findings can be primarily explained by the physiological process of age-related fatty infiltration. As individuals age, the functional acinar parenchyma of the major salivary glands, particularly the parotid gland, is gradually replaced by adipose tissue. 18 This fatty involution leads to a decrease in the functional cellular area (parenchyma) and alters the microstructural environment. Because adipose tissue has different diffusion characteristics and reduces overall cellular density compared to tightly packed healthy acini, water molecules experience less restricted motion, resulting in elevated ADC values. Furthermore, the interspersed fat within the parenchyma directly explains the shift from a homogeneous appearance (Grade 0) in younger adults to a more heterogeneous appearance (Grades 1-2) in older adults. This aligns with Kojima et al, who utilized signal intensity on fat-suppressed sequences to demonstrate that both heterogeneity and volume change as structural diseases like Sjögren’s syndrome progress. 15 Our data confirms that similar, albeit milder, heterogeneous changes occur purely due to natural aging.
Regarding gender differences, our study found no significant differences in ADC or heterogeneity between men and women. We did observe that the left submandibular area was statistically larger in men than in women. However, because this finding was lateralized (only observed on the left side) and not mirrored in the parotid glands, it is highly likely an artifact of sample size and uncorrected multiple statistical comparisons rather than true anatomical sexual dimorphism.
In the study conducted by Zhang et al, diffusion-weighted (DWI) MR imaging was used to evaluate physiological changes in the parotid gland before and after parotid-sparing radiotherapy and during taste stimulation, and showed that DWI with taste stimulation can be used as a tool for non-invasive evaluation of salivary gland function. 22 In the study conducted by Balçık et al, DWI was performed on patients with parotid gland tumors, and the average apparent diffusion coefficient (ADC) values of all lesions were calculated, and 28 benign and 13 malignant lesions were detected, and pleomorphic adenoma, Warthin tumor and malignant tumors could be distinguished using ADC values. 23 In the study conducted by Kojima et al, heterogeneity signal intensity on MR images and gland volume on T1 and fat-suppressed T2 images were compared in Sjögren’s patients, and it was observed that both the heterogeneous signal intensity increased and the submandibular and parotid gland volume increased as the disease progressed. 15
Prior literature has extensively focused on distinguishing pathologies rather than establishing baseline norms. For instance, Nada et al reported mean ADC values for normal superficial parotid lobes as approximately 0.89 x10-3 mm2/s and deep lobes as 0.97–1.02 x10-3 mm2/s, suggesting that combining morphological features with ADC is crucial for early detection of pathology. 24 In our cohort, the mean parotid ADC values were slightly higher (approx. 1.01 x10-3 mm2/s), which may reflect the wider age range and inclusion of older individuals with fatty infiltration in our study. Similarly, Balçık et al and Muñoz et al emphasized the utility of ADC in distinguishing benign pleomorphic adenomas from malignancies.23,25 However, the diagnostic utility of these thresholds can be compromised if the interpreting physician is unaware that older patients naturally exhibit smaller, more heterogeneous glands with slightly elevated baseline ADC values due to senescence.
Gamaleldin and colleagues performed MRI, MR sialography and sialendoscopy imaging on patients with suspected salivary gland stones before treatment. At the end of the study, MRI in conjunction with sialendoscopy was found to be false negative in 1 patient and missed 1 stone in 3 patients with multiple stones. It was observed that there was no statistically significant difference between the stone sizes detected by MRI and the actual sizes of the stones obtained by sialendoscopy. As a result, it was concluded that MR sialography is an accurate method to diagnose the presence, size and location of sialolithiasis and provides accurate ductal mapping to sialendoscopists. 26 In our study, we found sialolithiasis in only one (1.3%) of the 80 patients whose neck MRI images we examined.
Clinical Implications
For the ENT specialist and head and neck radiologist, these findings carry practical significance. When evaluating an older patient’s neck MRI, a heterogeneous parotid gland with a relatively higher ADC and reduced functional area should not be prematurely interpreted as an inflammatory condition (like chronic sialadenitis) or a diffuse infiltrative process. Instead, these are expected senescent changes. Recognizing this prevents overdiagnosis and unnecessary diagnostic interventions, such as fine-needle aspiration or sialendoscopy.
Limitations
This study has several limitations. First, due to the retrospective nature of the study, the health status of the patients was determined based on medical records, and subclinical conditions affecting the salivary glands cannot be entirely ruled out. Second, despite excluding known confounders, the heterogeneity grading relies on a subjective ordinal scale. Finally, treating age categorically in some analyses may have obscured subtle continuous trends, though this was mitigated by performing continuous correlation analyses. Future prospective studies with larger cohorts and histopathological correlations are recommended to validate these age-related normative thresholds.
Conclusion
This study demonstrates that the morphological and diffusion characteristics of the major salivary glands change significantly with age. Specifically, advancing age is associated with increased glandular heterogeneity and a negative correlation between parotid gland area and ADC values—likely due to age-related fatty infiltration replacing functional parenchyma. Establishing these baseline physiological variations is critical for clinicians; recognizing age-related fatty involution on MRI ensures that normal senescent changes are not misidentified as pathological conditions. Moreover, increase in heterogeneity in the salivary gland with age could be helpful in the diagnostic steps in MRI.
Footnotes
Ethical Considerations
This study is retrospective. Ethics committee approval was obtained from Kırıkkale University Non-invasive Research Ethics Committee (Date: 07.10.2021, Number: 2021/14).
Consent for Publication
All authors give consent for publication.
Consent-To-Participate
There is no need to take informed consent, because the data was evaluated retrospectively.
Author contributions
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data Availability Statement
All data for this study is presented in this paper.