Primary retroperitoneal lymphomas are a rare occurrence in clinical practice and their non-specific clinical presentation comprised primarily of constitutional symptoms. The diagnosis is difficult to attain without an extensive clinical and radiological workup, whereas a biopsy is necessary to confirm hematologic malignancy and exclude other possible etiologies.
Although lymphomas are considered to be one of the most common malignancies of the retroperitoneum, this location has been very rarely reported as the primary site   . Based on the underlying subtype, manifestations of the disease usually appear in different age groups. Namely, non-Hodgkin lymphomas are most frequently encountered in individuals between 40-70 years of age, whereas Hodgkin lymphoma has two peaks - at the end of adolescence and in late adulthood . It is not uncommon for lymphomas to affect various organs (liver, spleen, the gastrointestinal tract) and multiple lymph nodes, but despite its frequent systemic involvement, the clinical presentation commonly starts with a non-specific swelling of the abdomen and discomfort . Additional signs include painless lymphadenopathy (most commonly of the cervical lymph nodes), fever, weight loss, night sweats, and a palpable mass in the abdomen often discovered incidentally, which is more commonly identified in patients suffering from a Hodgkin lymphoma  . Rare signs include a painful ophthalmoplegia, numb chin syndrome (both signs of a systemic malignancy) and renal colic  .
Because the diagnosis is quite easily missed without a thorough workup, physicians must consider lymphomas in their differential diagnosis in the setting of unexplained constitutional symptoms. A properly conducted physical examination could reveal enlarged cervical lymph nodes during palpation of the neck and a mass during palpation of the abdomen. These findings require further workup through imaging studies. Plain radiography is not useful in the evaluation of soft tissues. For this reason, computed tomography (CT), often considered to be the diagnostic modality of choice, or magnetic resonance imaging (MRI) of the abdomen, thorax and pelvis are recommended  . A well-defined homogenous mass in the midline is often the characteristic feature of a lymphoma on CT, and compression or even displacement of various anatomical structures, such as the aorta, vena cava or iliac vessels, may be noted  . MRI, on the other hand, shows isointense (T1) or hyperintense (T2) images and a homogenous mass . Imaging criteria are not sufficient to confirm lymphoma, especially when almost a quarter of all Hodgkin lymphomas present as a heterogeneous mass . For this reason, a definite diagnosis is only made after performing a biopsy. Various approaches have been described in the literature, including CT-guided needle biopsy, nodal excision, and surgical resection    . Through microscopic examinations, immunohistochemistry and molecular studies performed on the obtained sample, the exact subtype of lymphoma can be identified, which is essential for choosing optimal therapy .