Teaching Case

70-year-old-man admitted to the Emergency Department for acute abdominal pain associated with diarrhoea, constitutional symptoms and abdominal distension. He had a medical history of heart transplantation.
An abdominal CT was performed and peritoneal fluid was aspirated and sent for cytological and microbiological analysis.
Despite intensive treatment he died of Multiple Organ Dysfunction Syndrome.

In a context of acute abdomen, a contrast-enhanced abdominal CT was performed, revealing:
-Enhanced and thickened omentum conforming an “omental cake” pattern, in association with areas of faint increased density.
-Diffuse peritoneal enhancement and low density peritoneal fluid.
-Stellated appearance of the mesenterium with areas of finely infiltrated fat.
-Diffusely distributed mesenteric adenopathies.
-Dilatation and wall thickening of the small bowel, worse defined at mesenteric side.

After solid organ transplantation, the incidence of cancer increases gradually. After 15 years, nearly 50% of heart cardiac recipients are diagnosed with some form of malignancy, and lymphoproliferative disorders represents 6-9% of them [1, 2], including a spectrum of disease ranging from polyclonal B-cell hyperplasia to lymphoma. Post-transplantation lymphomas are usually B-cell non-Hodgkings type [3].
Lymphoma is a common disease with some well-known imaging features. It affects the abdominal cavity, the most frequent findings are lymphadenopathies. The gastrointestinal tract is the most common extranodal location [4]. Peritoneal involvement is unusual and associated with the most aggressive histological subtypes [5]. Omental involvement is even rarer, due to the absence of lymphatic structures within it, but is thought to follow similar pathways as omental metastasis of gastrointestinal carcinomas.

The diagnosis of PL may be challenging for radiologists since other diseases have similar imaging features based on peritoneal and omental infiltration. Given the immunodeficiency scenario, the main differential diagnoses are peritoneal and omental seeding secondary to malignant diseases [6, 7] and peritoneal tuberculosis [8].
Biopsy or fluid samples are required to establish the final diagnosis. Early cytological or pathological examination avoid delays in treatment [9, 10], thus, considering this need for early diagnosis, certain radiological features may allow us to suggest that a peritoneal infiltration could be lymphomatous.
-Ascites is the most common finding, diffusely distributed, generally without loculation or septation. Carcinomatosis or tuberculous peritonitis generally presents with larger amounts of fluid and tends to loculate.
-Omental involvement could have two appearances: “Omental cake” (like peritoneal carcinomatosis) or a “smudged” omentum (faint and diffuse increased density).
-Mesenteric involvement presents as finely infiltrated fat or stellated appearance with thickened mesenteric folds.
-The peritoneum appears thickened (diffuse rather than nodular) and enhanced.
-Diffusely distributed lymph nodes (retroperitoneal and mesenteric), usually homogeneously attenuated, could also have central low attenuation and peripheral rim enhancement (similar to TBC).
-Diffuse small bowel wall thickening, generally poorly defined at mesenteric border, though peritoneal carcinomatosis presents as less defined at peritoneal side and primary GI lymphoma are seldom diffuse [11].

NHL is a serious complication after solid organ transplantation. PL is an infrequent presentation and treatment has the best chance of success if detected early. Even if the diagnosis of PL is highly challenging, CT findings can determine the need for a biopsy or fluid sample required to achieve final diagnosis.