Primary liver lymphoma: An extreme rarity differential on abdominal imaging

A 55-year-old male patient presented to the Emergency Department for evaluation of dull non-referring right hypochondrium pain for the past 3 months, which has increased recently since the past 2 days. There was also a history of one spike of undocumented fever in the last 2 weeks. There was no past history of any surgeries or any significant medical illness (Diabetes mellitus or hypertension, etc). There was no history of alcohol intake or previous history of any significant or recurrent episodes of jaundice. On examination, his vitals were normal and physical and systemic examination was unremarkable. Since there was upper abdominal pain along with history of fever, the patient was advised abdominal ultrasound and contrast-enhanced CT (CECT), suspecting hepatic abscess. CBC revealed mild lymphocytosis and markedly raised LDH.

Ultrasound scan showed a hypoechoic heterogeneous lobulated mass in the right hepatic lobe. Hepatic vessels were seen to be coursing through the lesion (Figures 1a and 1b). Abdominal CECT demonstrated iso-hypodense imperceptible lobulated mass lesion (Figure 2a) in segments V & VI of the right lobe, showing subtle peripheral enhancement on delayed venous portal imaging (Figures 2a to 2e). The lesion showed no early arterial phase enhancement, progressive contrast enhancement in the portal venous phase and hepatic venous phase, and absence of wash-out in the delayed phase. All these features suggested a non-hepatocellular origin of the mass lesion. The anterior branch of the right hepatic artery appeared prominent in the background of the hypodense mass lesion (Figure 2b). Mild perihepatic mesenteric fat stranding was noted (Figure 2e). On CT, the mass demonstrated well-lobulated contours with a peripheral enhancing pseudocapsule and a central hypodense area suggestive of necrosis (Figures 2d and 2e).

Primary hepatic lymphoma (PHL) represents a lymphoproliferative disorder isolated to the liver, devoid of any discernible engagement with the spleen, lymph nodes, bone marrow, or other lymphoid structures. Distinguishingly, non-Hodgkin’s lymphoma (NHL) frequently involves the liver as a secondary manifestation. PHL is an uncommon condition, constituting merely 0.016% of all NHL cases [1,2].

On ultrasound, primary hepatic lymphoma appears as a hypoechoic lesion with minimal vascularity within the mass lesion. The lesion may be solitary or multiple, with well-defined or irregular borders. The characteristic vessel penetrating sign (preserved intrahepatic vessels within the lesion) may be seen on US. However, these ultrasound features are not specific to PHL and can overlap with other hepatic lesions [3].

On contrast-enhanced CT scans, PHL may appear as a solitary hypodense hepatic lesion in over half of PHL patients (60%). These lesions may exhibit mild to moderate contrast enhancement in the arterial or delayed phases but generally less than the surrounding liver parenchyma. Less common radiological findings include multiple lesions (35–40%) and a diffuse infiltration pattern (5%), associated with a poorer prognosis. Due to its rarity and the lack of characteristic clinical, laboratory, and radiological features, PHL can be mistaken for primary hepatic carcinoma, metastatic liver diseases, or systemic NHL with secondary hepatic involvement [6].

On MRI, PHL lesions typically appear hypointense on T1-weighted images and hyperintense on T2-weighted images. On Gadolinium-based contrast MRI, lesions show moderate to marked enhancement in the portal venous and delayed phases [7].

Contrast-enhanced CT and gadolinium-enhanced MRI scans aid in further characterising liver lesions; however, the gold standard for diagnosis remains pathological examination [5].

In this case, crucial CT findings included a hypodense mass lesion that lacked enhancement in both arterial and venous phases. The lesion was seen to be encasing portal vessels without causing mass effects and absence of extranodal involvement.

The differential diagnoses of PHL include conditions such as liver abscess, hepatocellular carcinoma (HCC), cholangiocarcinoma and metastasis. Each of these conditions have distinct imaging features. Liver abscess usually appears as a well-defined, round or oval lesion that may contain moving echoes, which on contrast-enhanced scans show rim enhancement, whereas HCC may present as a hepatic mass with arterial phase hyperenhancement and washout in the portal venous or delayed phases on contrast-enhanced scans. Cholangiocarcinoma may demonstrate irregular bile ducts thickening or a mass that can enhance post-contrast, often with a delayed enhancement pattern. Metastasis may present as multiple hypodense lesions with contrast enhancement [8].

In the specific case described herein, the patient was initially referred from the surgery department under suspicion of a liver abscess due to the clinical features closely resembling amoebic liver abscess, a common occurrence in the Indian subcontinent. The absence of delayed peripheral rim enhancement and mass effect prompted consideration of an alternative diagnosis. Subsequent guided fine-needle aspiration cytology (FNAC) conclusively confirmed the presence of lymphoma.

Various therapeutic options available for cases of PHL include surgical interventions, chemotherapy, radiotherapy or a combination of these management options. In many cases, chemotherapy with cyclophosphamide, hydroxydaunorubicin, Oncovin and prednisone (CHOP) based chemotherapy regimens are commonly used [9].

Take home message

Primary hepatic lymphoma, though rare, should be considered in the differential diagnosis of any hepatic lesion presenting with non-specific upper abdominal pain and hypoechoic lesion on ultrasound. The characteristic “vessel penetrating sign”, if present, can suggest a strong possibility of PHL.

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