Background: Salivary MALT lymphoma represents the major complication of primary Sjögren’s Syndrome (pSS). However, the early recognition of MALT lymphoma may be challenging due to its indolent, slow clinical course.

Objectives: 1. to identify salivary gland ultrasonographic (SGUS) features and magnetic resonance (MRI) abnormal findings with Diffusion Weighted Imaging (DWI) and Apparent Diffusion Coefficient (ADC) of MALT in pSS patients 2. To evaluate the correlation between salivary gland ultrasonography (SGUS) and MRI in pSS patients with suspected lymphoma.

Methods: consecutive patients with pSS (2016 ACR/EULAR criteria) and suspected MALT lymphoma undergoing histological examination were included in this cross sectional study from September 2017 to November 2021. The US echostructure of each gland on B-mode images was graded using the latest 2019 OMERACT semiquantitative SGUS scoring systems (0-3). Sonographic features of focal lesions were described. Conventional MRI techniques (i.e T1WI, T2WI, and STIR images) combined with MR sialography was performed in all the cases. DWI was acquired at b-value 0, 500 and 1000. ADC values were calculated. Patients’ clinical and histological data were collected. Data were presented as mean±SD, or percent frequency as appropriate. Intergroup comparisons were made using the t-test/Mann–Whitney test for continuous variables and Fisher’s exact test for categorical variables.

Results: 45 pSS (mean age, S.D=55±15 yrs) were included. MALT lymphoma was histologically confirmed in 14/45 pSS patients and, specifically in 18/180 major salivary glands (17 parotids and 1 submandibular glands). At SGUS examination, MALT salivary glands presented an OMERACT grade 3 in 16/18 and a grade 2 in 2/18, significantly higher than the OMERACT scoring observed in no-MALT pSS glands (p=0.0001). The sonographic features more commonly detected in MALT were: hypoecoich macroareas with posterior enhancement, presence of septa or hyperechogenic strands and anarchic intralesional vascularization. At MRI, 15/18 (83.3%) MALT lymphoma appeared as intraglandular solid lesions: 9/15 (60%) were solid-cystic lesions and 6/15 (40%) were solid lesions without cystic changes. The frequency of solid lesions in pSS patients without lymphoma was 3/124 (2.4%), significanlty lower than in MALT-pSS. Furthermore 15/18 (83.3%) MALT lymphoma showed glandular fatty substitution. The presence of fatty substitution did not differ in MALT lymphoma and in no-MALT pSS glands. The mean (SD) ADC value of MALT lesions was significantly lower than the ADC of the parotid glands in pSS without lymphoma (0.63±0.07 x 10^-3 mm ² /s vs 1.13± 0.19 x 10^-3 mm ² /s, p =0.001). A negative correlation between SGUS OMERACT score and mean glandular ADC values (r = – 0.776, p < 0.001) was found; patients with OMERACT score 3 presented the lowest mean salivary gland ADC when compared to the other OMERACT scores (0-2) (p=0.001).

Conclusion: OMERACT semiquantitative SGUS scoring systems and MRI with DWI represent promising complementary tools in the differential diagnosis of pSS MALT lymphoma, particularly useful to guide parotid biopsy. Patients with an OMERACT score 3 in their SGUS deserve a careful screening for lymphoma.

Disclosure of Interests: None declared