Abstract

Hepatic granulomas are focal aggregates of transformed epithelioid histiocytes with or without multinucleated giant cells that are cuffed by lymphocytes and plasma cells. They represent delayed-type specialized cell-mediated immunity to a wide-spectrum of antigenic stimuli. Hepatic granulomas are found in up to 10% of liver biopsies and the causes are usually multifactorial. Different antigens like infectious agent, medication, foreign body and malignancy can initiate granuloma formation. Hepatic granulomas per se seldom cause architectural changes and often provide a clue to a systemic disease. Most often, to a practicing clinician, it is a combination of clinical presentation, laboratory parameters with information on the typical localization and characterization of the granuloma within the liver by the pathologist that often provides a clue to a definitive diagnosis.

Keywords: Hepatic granulomas, transformed epithelioid histiocytes, multinucleated giant cells, cell-mediated immunity, antigenic stimuli

Granulomas are aggregates of modified macrophages (epithelioid cells) and other inflammatory cells that accumulate after chronic exposure to an antigen and are seen in several systemic diseases. The extent of inflammation associated with formation of granuloma is variable. Bland granulomas have little or no associated inflammation. The term granulomatous hepatitis is used when the inflammation is severe, within or around the granuloma and granulomatoid reaction refers to a poorly delineated granuloma¹. The presence of a granuloma may be the first harbinger to an ongoing systemic disease.

Prevalence of Liver Granulomas

The prevalence of granulomas in liver biopsy ranges from 2.4% to 15%^2-9. Conn et al¹⁰ reported that 66% of their cases of granulomatous reaction were secondary to a systemic disease, 28% to primary liver disorders and 6% were idiopathic. The frequency of granulomas is reportedly high and ranges from 16% to 75% in select groups like patients with fever of unknown origin or those with a human immunodeficiency virus (HIV) infection¹¹. In India, granulomas are most often reported in tuberculosis (55%) followed by leprosy, sarcoidosis, histoplasmosis, brucellosis, amebic liver abscess, lymphoma, and malignant granuloma in that order¹².

Etiological Considerations

• Autoimmune: Sarcoidosis, primary biliary cirrhosis.
• Infections:
• Bacterial- tuberculosis, leprosy, brucellosis, Q fever, rickettsia, listeriosis, Bartonella, Tropheryma whipplei
• Parasites- schistosoma, leishmania
• Viruses- hepatitis C
• Fungal- Histoplasma.
• Drugs and chemicals.
•  

Histopathological Characteristics of Granuloma

A typical granuloma is an inflammatory reaction to a foreign body like microbial organism, drug, etc. It is essentially a compact spherical circumscribed lesion that consists of aggregated epithelioid histiocytes, measuring 50-300 µm. A typical granuloma consists of a central portion of macrophages and is surrounded by lymphocytes and fibroblasts. Differential diagnosis of a granuloma is largely based on its histological characteristics and the location within a hepatic lobule.

The histological variants include^13-15:

• Necrotizing (caseating): These are large and destroy the adjacent structures with no respect to the liver architecture. Common example is tuberculosis.
• Noncaseating: These are seen in sarcoidosis.
• Granulomatous inflammation: These are poorly formed granulomas with indistinct edges and consist of mixed inflammatory cells. Examples include drug-induced hepatocellular and/or ductular injury.
• Lipogranuloma: This is often seen in steatosis and comprises of aggregates of lipid-containing histiocytes, e.g., mineral oil.
• Microgranulomas contain 3-7 cells in cross-section, often admixed with other inflammatory cells and/or apoptotic hepatocytes. This pattern is nonspecific.
• Foreign body granulomas consist of inclusions of particulate material like mineral oil, starch and silicone within cytoplasmic vacuoles.
• Lymphohistiocytic granulomas are similar to epithelioid granulomas, but unlike the latter, these comprise of accumulations of macrophages and lymphocytes with distinct absence of epithelioid
• Fibrin ring or epithelioid granuloma: The fibrin ring or an epithelioid granuloma consists of a central lipid vacuole surrounded by a fibrin ring. The activated macrophages differentiate and aggregate to form giant cells or Langhans cells. These granulomas are seen in infections like cytomegalovirus, hepatitis A, leishmaniasis, toxoplasmosis, Q fever, drugs such as allopurinol and in Hodgkin’s disease.

Per se, granulomas can be located in almost all lobules. However, the distinct forms of necrosis as well as location of a granuloma can provide a clue to its origin and this helps in narrowing the differential diagnosis. For example, caseating necrosis is found in tuberculosis, while noncaseating necrosis is common in sarcoid granulomas¹⁶. The latter are located in the portal and periportal regions. In primary biliary cirrhosis, granulomas are seen near the porta. The drug-induced granulomas are poorly defined and are located anywhere within the hepatic lobules¹⁶.

Pathogenesis

The failure of humoral or cellular immune response to eliminate the offending foreign material leads to granuloma formation¹⁷. Granulomatous reaction is essentially of 2 types, i.e., an immunological reaction to either an inert foreign body or to an active antigen¹⁸. The response to the agent depends on whether it is located within or outside the cell. For intracellular agents, there is a Th1 response while for extracellular, there is a Th2 immunological response. With the former, several cytokines such as interferon-γ, interleukin (IL)-2 and IL-12 are produced soon after phagocytosis of the agent by the macrophages, which reduce them to small peptides. With the Th2 response, there is secretion of IL-4, 5, 6 and 10. A vicious cycle ensues wherein by positive feedback mechanism the cytokines constantly stimulate the T cells. Thus, the formation and maintenance of liver granulomas is based on cytokine release¹⁶.

With the release of cytokines, clusters of histiocytes and lymphocytes are seen. The histiocytes and macrophages are transformed into epithelioid histiocytes, which conglomerate to a granuloma. The latter have abundant pale cytoplasm. Apart from cytokines, epithelioid cells in particular, within a granuloma secrete proteins like collagenase, lysozyme, and angiotensin-converting enzyme (ACE) (e.g., sarcoidosis)¹⁸. Elevated ACE levels suggest an active sarcoid.

Typically surrounding the granulomatous reaction is a cuff of lymphocytes, a few plasma cells and eosinophils. Multinucleated giant cells are result of fusion of macrophages. Granulomas when infiltrated by eosinophils are suggestive of either a drug reaction or a parasitic infection. Thus macrophages play a key role in granuloma formation while tissue necrosis (necrotizing granulomas) is largely initiated by epithelioid histiocytes, characteristically seen in infections like tuberculosis.¹⁹

Accumulation of these effector cells in the portal tract leads to injury of the septal and interlobular bile ducts that can cause cholestasis¹⁶.

Clinical Presentation

Majority of the patients are asymptomatic at presentation or have clinical manifestations of underlying systemic disease. Nonspecific symptoms include fever (tuberculosis, sarcoidosis, infectious disease), weight loss, anorexia, and night sweats. Lymphadenopathy may be present in systemic diseases^19-23.

Two-thirds of patients have a hepatomegaly with an elevated alkaline phosphatase and gamma-glutamyl transferase.²¹ Jaundice is rare unless there is bile duct injury. Portal hypertension is reported in schistosomiasis (noncirrhotic portal hypertension), sarcoidosis and primary biliary cirrhosis¹⁶. Final diagnosis is at histology.

Diagnostic Evaluation

A comprehensive medical history and physical examination should be pursued along with an extensive medication and travel history. Symptoms and signs are helpful in developing a differential diagnosis. Blood investigations, serological tests and biopsy lead to a definitive diagnosis. Ultrasound can detect a hepatomegaly. Granulomas of 0.5 cm in diameter or greater can be identified on magnetic resonance imaging (MRI) as multiple nodular lesions or, less commonly, isolated hepatic granulomas. Caseating granulomas as in tuberculosis have a high or low signal in T1-weighted MRI, and no enhancement or sometimes peripheral enhancement after gadolinium injection in comparison to noncaseating granulomas in sarcoidosis, which have intermediate signals on T1-weighted images with gadolinium enhancement that may or may not persist on late images^24-26. However, these findings are operator dependent and difficult to interpret.

In a study²⁷ on 251 explant livers, we found the prevalence of liver granulomas to be 7.2%. Five patients who had undergone transarterial chemoembolization prior to transplantation, had foreign body granuloma. Five patients were diagnosed to have caseating granulomas and were started on four drug regimen for tuberculosis - isoniazid, rifabutin, pyrazinamide, and ethambutol. All responded well to treatment. Three patients with hepatitis C virus infection showed portal microgranulomas/granulomas. These were compact, non-necrotizing, epithelioid granulomas of varying sizes observed within portal tracts and lobules. Five cases, where the diagnosis of granulomas remained elusive, isoniazid prophylaxis was given for 9 months to reduce the risk of reactivation of tuberculosis.

The presence of granulomas suggestive of tuberculosis in the explant liver is associated with the development of tuberculosis in the recipients²⁸. Granulomas in hepatitis C virus patients could be due to an interferon-mediated stimulation of Th1 immune response or intravenous drug use²⁹.

The differential diagnosis (Table 1) for hepatic granulomas can be broadly classified as those associated with:

• Infections
• Drugs
• Autoimmune disorders
• Malignancy
•  

PHT = Portal hypertension; SAP = Serum alkaline phosphatase; GGT = Gamma-glutamyl transferase; PBC = Primary biliary cirrhosis; AMA = Antimitochondrial antibodies; LFT = Liver function tests; AFB = Acid-fast bacilli; TB = Tuberculosis; HIV = Human immunodeficiency virus; CMV = Cytomegalovirus; HCV = Hepatitis C virus; HCC = Hepatocellular carcinoma; NASH = Nonalcoholic steatohepatitis; TACE = Transarterial chemoembolization; ESR = Erythrocyte sedimentation rate.

Conclusions

Hepatic granulomas are of multifactorial origin. A definite diagnosis regarding the granulomas can only be made using clinical data and histopathology. In a quarter, the cause for a granuloma remains unknown. In Indian setting, treatment for tuberculosis should be initiated in presence of caseating granulomas and a high index of disease suspicion.

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