Hepatic lymphoma is usually a secondary liver lesion that occurs in more than 50% of patients with Hodgkin's disease (HD) or non-Hodgkin's lymphoma . Although primary hepatic lymphoma does exist, it is extremely rare because the amount of lymphatic tissue in the liver is very small, present only in the periportal spaces.
Primary hepatic lymphoma has been reported in middle-aged men infected with the human immunodeficiency virus, in patients under pharma-cologic immunosuppression, and in organ transplant recipients. In the first two groups of patients, the lymphomatous process includes a spectrum of lymphoproliferation from benign B-cell hyperpla-sia to malignant monoclonal non-Hodgkin's lymphoma. An association has been identified between post-transplant lymphoproliferative disorders and Epstein-Barr virus infection. At the time of lymphoma diagnosis, more than 80% of post-transplant patients are infected with the Epstein-Barr virus [36,94].
Whereas numerous miliary small nodules may be present in the liver in well-differentiated non-Hodgkin's lymphoma, in less well-differentiated non-Hodgkin's lymphomas, the lesions are often larger and more infiltrative. In Burkitt's lymphoma, subcapsular infiltration may also be found as a consequence of peritoneal spread .
In Hodgkin's lymphoma, the hepatic involvement may range from multiple small nodes to large infiltrations. This involvement occurs more frequently with lymphocyte depletion and mixed cellular subtypes than with the lymphocyte-rich subtype of HD. Concomitant peliosis hepatis may also be present .
Hepatic lymphoma initially spreads in the portal areas in which the majority of the lymphatic tissue is present . In HD, a Reed-Sternberg variant cell-type can be detected microscopically. In non-Hodgkin's lymphoma the lymphocytic form tends to be miliary, whereas the large cell or hystiocytic varieties appear as nodular masses .
Clinically, patients with primary non-Hodgkin's lymphoma most often present with pain in the right upper abdominal quadrant or with hepatomegaly. Secondary lymphomas, as well as Hodgkin's lymphoma, may induce jaundice, fever and hepatomegaly, but unfortunately these signs are nonspecific and in some cases may even result from chemotherapy .
On US, both Hodgkin's and non-Hodgkin's lymphoma commonly appear as single or multiple hypoechoic masses, often with indistinct margins. Multiple hypoechoic lesions may mimic the appearance of a diffuse infectious process such as candidiasis. In the diffuse lymphomatous form the echogenicity of the hepatic parenchyma may be normal or heterogeneous and the overall architecture of the liver may be altered. Occasionally, patients with non-Hodgkin's lymphoma have echogenic or target-like lesions . If there is bleeding within the tumor, the ultrasonographic characteristics of a cyst may be seen .
On non-enhanced CT images, HD and non-Hodgkin's lymphoma generally appear as homogeneously hypodense, sharply marginated nodules. After contrast medium administration the lesions appear hypodense, although a weak enhancement may be detected (Fig. 38). In the miliary form, a diffuse decreased attenuation may be observed, which is indistinguishable from fatty infiltration .
On MR images, focal hepatic lymphoma is generally seen as homogeneously hypointense compared to the normal parenchyma on unenhanced T1-weighted images and hyperintense on T2-weighted images. Dynamic imaging after the administration of a gadolinium contrast agent typically reveals a hypointense appearance on arterial phase images, followed by homogeneous, delayed enhancement on portal-venous phase images and isointensity on equilibrium phase images (Figs. 39, 40). Susceptibility artifacts may be caused by hemorrhage in pre-treated focal infiltrations and may be more clearly delineated on fat-suppressed T1-weighted images . Although lymphoma is readily distinguishable from normal liver, the difference in relaxation times from metastases and HCC is not significant.
In cases of diffuse infiltrative lymphoma, no significant differences are seen between normal liver parenchyma and the lymphomatous liver infiltration.
Fig. 38a-c. Primary hepatic lymphoma on CT. On the unenhanced CT image (a) a huge, slightly hypodense mass (asterisk) can be seen. The lesion shows weak, heterogeneous, and mainly peripheral enhancement during the arterial phase (b), and remains heterogeneously hypodense in the portal-venous phase (c)
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