Diagnosis of diffuse spleen involvement in haematological malignancies using a spleen-to-liver attenuation ratio on contrast-enhanced CT images.

Objectives: We aimed to test the hypothesis that the spleen-to-liver-attenuation ratio on portal-venous enhancement phase CT images can identify diffuse splenic infiltration in subjects with lymphoma.

Methods: A database search yielded 70 subjects with malignant haematological diseases who underwent contrast-enhanced CT (CECT) between December 2010 and March 2018. Additionally, consecutive control subjects were evaluated. We compared the splenic volume, splenic attenuation, spleen-to-liver, spleen-to-aorta and spleen-to-musculature ratios on portal-venous phase CECT images, pre- to post-treatment and between the different lymphoma entities. The standard of reference for splenic involvement was normalisation of the spleen volume following chemotherapy or normalisation of FDG-uptake.

Results: In subjects with diffuse splenic involvement, the spleen attenuation was significantly lower before treatment (93.48 HU) compared to controls (112.39 HU; p < .01) and after successful treatment (113.39 HU; p < .01). The spleen-to-liver attenuation ratio significantly increased after treatment (p < .001) and proved significantly lower at baseline when compared to control subjects (p < .01). The spleen volume significantly decreased after successful treatment (from 586.14.87 cm to 284.90 cm; p < .001). Spleen-to-liver ratio significantly increased in lymphoma patients after therapy, inversely correlating with the decline in FDG-uptake (n=10) even in patients with normal-sized spleens (2/10), staying unchanged at follow-up. The outcome variables were not significantly different between the lymphoma subtypes.

Conclusions: We suggest the additional use of spleen-to-liver attenuation ratio to splenic volume alone for detection of diffuse splenic infiltration in subjects with lymphoma. The course of spleen-to-liver attenuation ratio inversely correlated with that of FDG-uptake in a subgroup of patients working accurately in normal-sized diffusely involved spleens.

Key Points: • Involvement of the spleen is frequent in haematological malignancies and is important for staging and appropriate treatment. • Diffuse splenic infiltration often results in only homogeneous splenomegaly without a focal lesion, but even no or only minimal increase in splenic volume is possible. In these cases diagnosis of spleen involvement is a challenge for the radiologist. • Our data support the use of the spleen-to-liver attenuation ratio in addition to size measurements for the detection of diffuse splenic infiltration in subjects with lymphoma.