Lymphoma arises in the lymph nodes or in the lymphoid tissue of parenchymal organs such as the gastrointestinal tract, spleen, lung, or skin. Ninety percent of cases of Hodgkin’s disease originate in the lymph nodes; 10 percent are of extranodal origin. In contrast parenchymal organs are more often involved in non-Hodgkin’s lymphomas; about 40 percent of these lymphomas are of extranodal origin.
The spleen is often affected in patients with lymphoma of both the Hodgkin’s and non-Hodgkin’s types. The best imaging modality is CT, which most commonly demonstrates splenomegaly with or without focal low-density nodules in the parenchyma. However, if there is homogeneous lymphomatous infiltration of the spleen without enlargement, the CT appearance may be normal.
The manifestations of lymphoma involving the gastrointestinal tract are discussed in Chapters 22, 23, and 24. Intrathoracic lymphoma is described in Chapter 10.
Once the diagnosis of lymphoma is made, it is essential to determine the status of the abdominal and pelvic lymph nodes. This is necessary for both the initial staging and treatment planning and for assessing the efficacy of treatment and detecting tumor recurrence.
There is controversy about the best radiographic approach for the staging of a patient with known lymphoma. Although lymphography has long been the most accurate examination for demonstrating lymphomatous involvement of abdominal and pelvic lymph nodes, non-invasive cross-sectional imaging techniques (CT and ultrasound) are now considered by many to be the diagnostic methods of choice. Unlike CT and ultrasound, which rely primarily on an increase in node size as a criterion for determining tumor involvement, lymphography can detect microscopic tumor foci and alterations in architecture within normal-sized nodes. It also can distinguish large nodes that contain tumor from similarly enlarged nodes that demonstrate only benign reactive changes. Following formal staging procedures, postlymphography abdominal radiographs can provide an inexpensive and accurate means of assessing therapeutic efficacy and detecting relapse. However, the lymph nodes in the upper para-aortic, retrocrural, renal hilum, splenic hilum, porta hepatis, and mesenteric areas cannot be adequately examined by lymphography and require CT or ultrasound. Computed tomography is also useful in delineating the exact extent of the tumor mass. It often shows that the abnormality demonstrated with lymphography is only the tip of the iceberg and that more extensive disease, possibly important in planning radiation treatment, is actually present. Computed tomography can also be used to follow the response to treatment, especially since there may be insufficient residual contrast on postlymphography abdominal films to make a diagnosis.
In practice, CT is generally the first procedure employed in staging patients with lymphoma, especially those with non-Hodgkin’s lymphoma that tends to produce bulky masses in the mesenteric and high retrocrural areas, where the contrast material used in lymphography does not reach. An abnormal CT scan eliminates the need for the more invasive lymphography; a normal CT scan obtained at 2-cm intervals can exclude retroperitoneal adenopathy with high confidence. Lymphography is of value primarily in Hodgkin’s disease, which infrequently involves the mesenteric nodes, often does not produce bulky masses, and may cause alterations of internal architecture only (which cannot be detected with CT) in normal-sized nodes. Lymphography is also indicated when CT is equivocal because of either a lack of fat or gross motion artifact.