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LIVER TRANSPLANTATION - Role of Histopathologist

Anjali Amarapurkar
Asso. Prof, Dept. of Pathology, TN Medical College, BYL Nair Charitable Hospital,
Mumbai - 400 008.



 

Organ transplantation is no longer experimental procedure. Thousands have been benefited from the organ transplantation done in various centres all over the world. Until now in India, the only form of organ transplantation possible was kidney from living donors. But with the transplantation of human organ act in 1994, it is expected that India will not lag behind in this field. Liver transplantation is one of the most challenging therapies available for acute and chronic end stage liver disorders. First successful human liver transplantation was performed by Dr. T Starzl in United States and Sir Roy Calne in United Kingdom in the 1960s [1, 2] Following advance in organ preservation, patient’s selection criteria, surgical techniques and control of rejection, the survival rates of 80-90% at one year can be achieved in low risk elective recipients. Several studies have now confirmed the marked improvement in the quality of life following successful transplantation. [3-9]

Liver transplant is a teamwork, which requires close cooperation, understanding and co-ordination from a variety of disciplines including clinicians, pathologists, nursing staff, blood bank, laboratory workers and many other supportive staff. Pathologist is an integral part of any transplant team. The pathology of organ transplantation is known as "Transplant Pathology". In transplant services, pathologist is involved in making decision regarding the therapy or management of the patient or indicating possible complications.

Role of pathologist in liver transplantation

Liver biopsy procedure

Liver graft is usually soft and percutaneous biopsy using standard 14 G (1.9 mm) Menghini suction needle is preferred method. Usually the biopsy is well tolerated by the patient because the liver capsule is denervated. Contraindications of biopsy are same as that of non-transplant cases. The biopsies are performed as protocol biopsies or whenever required, particularly in the early post-transplant period, initiation of treatment is dependent on the results. Tissue is processed urgently, to obtain adequate H and E sections within 3 to 3.5 hours of the biopsy.

Liver biopsy is viewed by most investigators as the gold standard for monitoring the graft and is used to detect allograft rejection, technical complications related to anastomosis of biliary tract and blood vessels, detection of opportunistic infections within the graft, recurrence of the host’s previous illness and drug reactions. [10-13] The most important uses of the biopsy are diagnosis and monitoring of allograft rejection. One of the difficult tasks of examining a post transplant liver biopsy isrecognizing changes of rejection verses changes of infection in an immuno-compromised host. Liver allograft changes are divided according to the relation to time after transplantation [14] (Table 1). We evaluated total 47 cases of liver transplantation occurred at the King’s Hospital, London in last few months in 1998.

The commonest indication of liver transplantation was cirrhosis. The aetiology being hepatitis B, C, alcoholic, cryptogenic and chronic long standing cholestasis. Acute liver failure is another indication for liver transplantation. Out of 11 cases of acute liver failure, 5 were non A non B non C hepatitis, 4 paracetamol overdose, one was fulminant hepatic failure due to hepatitis A and remaining case was autoimmune hepatitis leading to acute liver failure. Primary biliary cirrhosis and primary sclerosing cholangitis also make major contribution. Amongst the paediatric age group, biliary atresia with failed Kassai and metabolic diseases are the important indications for transplant. Miscellaneous group includes a case of Budd Chiarri, 1 neonatal hepatitis and 2 liver tumours of which one was hepatocellular carcinoma diagnosed preoperatively in alcoholic cirrhosis and another was primary hepatic carcinoid tumour (Table 2).

TABLE 1
Liver allograft complications in relation to time, after transplantation
Early complications
(1-3 weeks)
Delayed complications (3 weeks - 3 months) Late complications(> 3 months - year)
Hyperacute rejection Chronic rejection (Ductopenic / vascular) Late cellular rejection
Preservation injury   Chronic rejection
Acute cellular rejection Biliary obstruction Late biliary complications
Primary graft non-function (Acute graft failure) Ascending cholangitis Chronic hepatitis
Functional cholestasis Viral hepatitis (Hep B, C, CMV, HSV, EBV) Recurrence of disease (Hep. B, C, PBC, PSC) Lymphoproliferative disorders (Lymphoma

 

TABLE 2
Indications for liver transplantation
Indications n=47 Percentage (%)
Cirrhosis 18 38.29
Hepatitis B 3 6.38
Hepatitis C 8 17.02
Alcoholic 3 6.38
Cryptogenic 2 4.25
Chronic cholestasis 2 4.25
Acute liver failure 11 23.40
Primary biliary cirrhosis 5 10.63
Primary sclerosing cholangitis 4 8.51
Biliary atresia 4 8.51
Tumours 2 4.25
Miscellaneous 3 6.38
Budd chiarri 1 2.12
Metabolic (Glycogen storage) 1 2.12
Neonatal hepatitis 1 2.12

Out of 47 cases 68% showed changes of acute cellular rejection on histology. Except one, all of them responded well to immunosuppressive therapy. The remaining one subsequently landed up in chronic rejection. Graft failure was found in 7 cases (14%) of which chronic rejection was seen in one case, generalised sepsis 1, technical difficulty leading to ischaemic necrosis of the graft 1 case and in 4 cases recurrence of hepatitis B and C was noticed. All those 7 cases required retransplantation. Disease recurrence in hepatitis B, C is known and thought to be due to presence of viruses in circulation and at the extrahepatic sites (Table 3).

TABLE 3
Graft failure in liver transplantation
Graft loss n=7 Within 1st month 1-6 mth. 1 year > 1 year
Chronic rejection 1 1
Septicaemia 1 1
Surgical/technical problems 1 1
Disease recurrence 4  
Hepatitis C 3 1 2
Hepatitis B 1 1

Liver allograft rejection

Acute cellular rejection - It can be defined as cell mediated immune reaction, precipitated by genetic or possibly environmental differences between the donor and recipient, that has the potential to injure the allograft. [15]

It is the most common cause of graft dysfunction, incidence being 50-80%. [14,16] This can occur upto 1 year of post transplant period. However the peak incidence is between 5 and 15 days. Clinical findings are often absent in early or mild acute rejection but as the severity increases the signs and symptoms of fever, right hypochondriac pain, jaundice, raised transaminases are seen. The bile production decreases with pale, watery bile. Majority of these patients show recovery. As the time after transplantation increases, acute rejection becomes much less common, unless the patient has less than adequate immunosuppressive drug levels.

The pathophysiology of acute rejection is triggered by direct alloantigenic stimulation of recipient T lymphocytes by donor dendritic cells (DC). [17] These DC are antigen presenting cells, located amidst collagen bundles supporting the terminal lymphatic channels in portal tracts and terminal hepatic venules. They normally monitor the influx of potentially dangerous antigens. Theactivated recipient T cells form clusters with donor DC secrete cytokines that results in localization of inflammatory cells within portal tracts. [18] Bile ducts are specifically targeted for damage in acute rejection. This is because, the biliary epithelial cells and basement membrane of bile ducts normally express immunologically active antigen and participate in immune responses, the liver biopsy is considered as a ‘gold standard’ for acute rejection. [10] The classic triad defined by Snover et al [19] in the liver tissue consists of mixed portal tract inflammation, bile duct damage and venular endothelitis (Fig. 1). The portal inflammation often varies in intensity from one part of the biopsy specimen to another. Lymphocytes are the predominant cells, include significant number of activated and blast cells. On immunostaining, majority of them are CD 8 + and to a lesser extent CD 4 + cells. In addition, there are fair number of neutrophils and eosinophils. Foster et al20 found that, more than 7% of eosinophils in portal infiltrate was the most sensitive and specific feature for diagnosing acute rejection. The bile duct damage is seen in the form of vacuolation of the epithelium with nuclear irregularity, pyknosis, and infiltration by lymphocytes and neutrophils and focal disappearance referred to as rejection cholangitis. Endothelitis or venulitis is in the form of attachment of lymphocytes to the venular endothelitis, which may be lifted up, with formation of a clear subendothelial space in which lymphocytes accumulate. Although not a prerequisite, endothelitis is the most reliable sign of rejection in early stages. Acute cellular rejection can be graded histologically as mild, moderate and severe depending upon the periportal inflammatory spillover, cholestasis, sinusoidal endothelitis and perivenular necrosis. [21] The differential diagnosis for acute rejection during the first 6 weeks after transplantation is limited to few disorders. This is because most other causes of allograft dysfunction during this time, such as vascular thrombosis, ischaemic preservation injury, functional cholestasis and humoral rejection are not associated with a significant mononuclear portal tracts. Perivenular infiltrate containing small and blastic lymphocytes, eosinophils, and neutrophils. Thus, the diagnosis of acute cellular rejection is normally not difficult to establish within first 15 days. The problem occurs when histological features are very minimal. In this situation clinicopathological correlation is very essential. The late acute rejection episodes can be broadly separated into 2 time periods, 1-6 months and more than 6 months - 1 year after transplant during which different diagnostic considerations arise which can be excluded with the help of liver histology, clinical features and other diagnostic tests [15] (Table 4).

Fig 1
Fig.1 : Acute cellular rejection showing portal inflammaation, bile duct damage and endothelities. (HE 100 x).

 

TABLE 4
Differential diagnosis of late onset acute rejection
1 to 6 months post transplant > 6 months to 1 year post transplant
CMV hepatitis Recurrent / denovo hep B, C
EBV hepatitis and autoimmune liver disease
Post transplant obstructive cholangiopathy
lymphoproliferative disorder adverse drug reaction
Recurrent/denovo hep B, C

Chronic allograft rejection - It is a major cause of graft failure and retransplantation. Prevention and early diagnosis of chronic rejection remains an important clinical challenge to the liver transplant team. In contrast to acute cellular rejection, chronic rejection is a difficult diagnosis, due to inconsistency, insidious development and uneven distribution of histological changes. An international group has defined chronic rejection as an irreversible form of organ dysfunction, generally occurring more than 60 days post-transplant and characterized by 2 major histologic findings : obliterative vasculopathy and loss of small bile ducts. [22] The reported incidence varies from 2.4 to 16.8%, [23] which is falling sharply over time due to stronger immunosuppressive such as FK 506, which arrest the progress of chronic rejection in its early stage. [24] Chronic rejection may develop following repeated episodes of acute rejection or evolve independently. It is characterized by increase in jaundice, relentless increase in markers of cholestasis including serum alkaline phosphatase and GGT. The basic mechanism of cholestasis includes serum alkaline phosphatase and GGT. The basic mechanism of chronic rejection is the prolonged repeated exposure to allograft antibodies, which are responsible for endothelial damage giving rise to foam cell arteriopathy. The loss of bile ducts is thought to be either due to direct immunological damage or ischaemic damage produced by foam cell arteriopathy. [25, 26]

On histological examination though ductopenia and foam cell arteriopathy are the cardinal signs of chronic rejection, in early stages it is difficult to interpret the biopsy and repeat specimens are often needed to reach a diagnosis. Ductopenia is the defining histological feature. The diagnosis can be made with confidence if 20 or more portal tracts can be reviewed and if 50% of these lack interlobular bile ducts. [27] It is important to note that the ductules (cholangioles) should not be counted as ducts. The foam cell arteriopathy is characterized by accumulation of lipid-laden macrophages in the intima of the arteries causing occlusion of the lumen (Fig. 2). This foam cell arteriopathy is rarely sampled in the biopsy specimen since most affected arteries are outside the reach of the biopsy needle, in large portal tracts or in perihilar soft tissues. Other histological features seen in chronic rejection are mild portal infiltrate, cholestasis and perivenular cell loss. Difficulties in biopsy interpretation may arise from factors which are inconsistently associated with chronic rejection such as strictures of major bile duct, non-rejection related ischaemic cholangitis secondary to thrombotic occlusion of hepatic artery or primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC), in these cases ductular proliferation is more pronounced, vanishing of interlobular bile ducts may be delayed with progressive periportal fibrosis, which is not a prominent feature in otherwise classic chronic rejection. [14] Finally, increased use of liver biopsy and development of standardized criteria for histological diagnosis of chronic rejection has resulted in early diagnosis and an overall reduced incidence of graft loss related to chronic rejection. The possibility of disease recurrence after transplant must form part of the evaluation of all liver allograft recipients. In some situations, recurrence or reinfection is clearly identifiable and has significant impact on both the quality and the length of patient’s survival. Such examples include viral infections like hepatitis B, C and most of the primary or secondary liver tumours. [28-32] At the other end the disorders such as PBC or PSC, disease recurrence is controversial, since there is little impact on the quality or length of patient’s life. [33-34] Lymphoproliferative disorders account for about 1-2% of the reported instances of malignancies complicating immunosuppression. [35] Most cases affect B cells and can be linked to EBV infection. Primary or reactivated EBV infection of B cells produces mononucleosis like disease or involves into true monoclonal B cell lymphoma. Other adverse drug effects can also occur which are ranging from cholestasis to even hepatocellularcarcinoma. [36, 37]

Fig 2
Fig. 2 : Foam cell areriopathy of chronic rejection. (HE 100 x).

In summary, considering that the main criteria for selection of patients for liver transplantation is the presence of end stage liver disease for which all other available therapies have proved ineffective, liver transplantation results in a remarkable improvement in the quality of life. In adult population, waiting lists for liver transplant can be anticipated to grow further. But the limitations in organ availability are particularly acute in the paediatric age group despite the recent innovative techniques of reduction of ‘split graft’. Although transplantation clearly improves survival, the quality of life following have gained increasing importance with the recognition that medical resources are limited and that medical technology must be applied selectively.

ACKNOWLEDGEMENT

Author gratefully acknowledges RD Birla Smarak Kosh Medical Research Centre, Bombay Hospital, Mumbai for the financial assistance and also would like to acknowledge. Dr. BC Portmann, a Consultant and Chief Hepatopathologist, King’s Hospital, Liver Institute at London for allowing me to study the liver transplant cases.

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