Primary hepatic lymphoma

Primary hepatic lymphoma (PHL) is very rare, with approximately 100 described cases. If it is being considered as a diagnosis, distant lymphadenopathy, splenomegaly, bone marrow disease, and leukemia should not be present for at least 6 months after the liver tumor has been detected (see: secondary hepatic lymphoma) ⁴.

Epidemiology

It is a rare presentation of lymphoma (<1% of all non-Hodgkin lymphomas).
In contrast, according to one source, diffuse large B-cell lymphoma (DLBCL) affects around 7 out of 100,000 people annually in the United States, with potential for secondary involvement of the liver. Therefore, secondary hepatic lymphoma is much more common.

Clinical presentation

The most common presentation includes abdominal pain, jaundice, and weight loss. The majority of patients will have elevated liver enzymes, although these may be normal. The typical age of presentation is around the age of 55 years. It has a male preponderance.

Pathology

The exact cause of this primary hepatic lymphoma is still unclear; however, it is primarily found in immunocompromised patients due to AIDS/HIV, congenital immunodeficiency, collagen vascular disease, and immunosuppressant therapy for organ transplant. Reports have also shown infections as a probable cause, including EBV, HIV, hepatitis C and hepatitis B with chronic hepatitis and cirrhosis.

Diffuse large B-cell lymphoma comprises the majority of cases of primary liver lymphoma. Other histologic types include peripheral T-cell leukemia/lymphoma not-otherwise-specified, follicular lymphoma, mantle cell lymphoma, and Burkitt lymphoma.

Radiographic features

Primary hepatic lymphoma is most commonly seen as a solitary mass (53-65%). It does not have characteristic radiographic features and can often be mistaken for other liver tumors. Liver biopsy is the most specific means of making the diagnosis.

Ultrasound

Ultrasound is usually the initial radiological test performed:

• typically hypoechoic to the liver parenchyma, probably due to high cellularity and lack of background stroma
• rarely, they may be so hypoechoic as to appear similar to a cyst
• occasionally have a "target" appearance with a central hyperechogenicity and outer hypoechogenicity
• increased peripheral vascularity on color Doppler

CT

• frequently a single (~60%), solid, hypoattenuating (due to hypovascularity) hepatic lesion, as opposed to secondary lymphoma, which can be more diffusely infiltrating ^1,2
• there can be a large variation in size, but primary hepatic lymphoma tends to have a dominant mass, as opposed to secondary lymphomatous involvement of the liver, which tends to be more diffuse
• variable contrast enhancement on CT, but tend to be hypoenhancing relative to liver on all phases, with no enhancement in some cases
• can present as an ill-defined mass at the porta hepatis
• can have hemorrhage, necrosis, and rim enhancement

MRI 

MRI findings depend on the extent of infiltration.

• T1: typically hypointense relative to remainder of liver
• T2: often shows variable intensity
• T1 C+ (Gd):  these lesions show poor enhancement but may show faint peripheral rim enhancement 
• DWI/ADC: restricts diffusion, even in comparison to liver parenchyma, as it is hypercellular

Signal characteristics are almost identical to secondary lymphomatous involvement but manifestation as a single solid mass may favor a primary hepatic lymphoma ¹.

Nuclear medicine

PET-CT

PET-CT is useful in making the diagnosis and can also be used for staging.

• FDG-PET
  • ​avid FDG uptake of the lymphomatous mass in the liver
  • can show or exclude extrahepatic sites of lymphoma with a high degree of sensitivity

Treatment and prognosis

Primary hepatic lymphoma is primarily treated with chemotherapy. R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) is the most common chemotherapy regimen for advanced diffuse large B-cell lymphoma (DLBCL). In the United States, this regimen is generally given every three weeks for 6 to 8 cycles. Other treatment options include radiation therapy or surgery.

Differential diagnosis

• secondary hepatic involvement of the liver from non-Hodgkin lymphoma: much more common
• infection/abscess in a patient receiving chemotherapy
• hepatocellular carcinoma: more common
• metastatic disease to the liver: patient without known lymphoma