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Liver transplant biopsy interpretation: Diagnostic considerations and conundrums Rastogi A



   Abstract  

Liver transplantation is now a well-established therapeutic strategy for irreversible acute and chronic liver diseases. There is a broad spectrum of complications encountered in early and late period after transplantation and these contribute to significant morbidity and mortality. Distinguishing among these complications often requires interpretation of allograft biopsies. Histology is the gold standard for the diagnosis of rejection. However, interpretation of these biopsies is quite challenging due to the atypical and complex histomorphology. Multiple simultaneous insults, effects of immunosuppression (IMS), de novo complications, and presentations distinct from non-transplant setting are a few cardinal concerns. Awareness of the time period of occurrence of various complications, the most characteristic histological features or patterns, and distinguishing features between various complications are crucial. The management can be completely divergent; hence, recognition of dominant problem and interpretation in appropriate clinical context is much needed. This review focuses on histopathology of major complications accountable for early and late graft dysfunction. Tabulation of clinico-pathological features to distinguish various complications helps to solve the conundrums and arrive at the correct diagnosis.

Keywords: Allograft biopsy, early graft dysfunction, late graft dysfunction, liver transplant, recurrence, rejection

How to cite this article:
Rastogi A. Liver transplant biopsy interpretation: Diagnostic considerations and conundrums. Indian J Pathol Microbiol 2022;65:245-57




   Introduction   Top

Liver transplantation is a well-established therapeutic strategy for irreversible acute and chronic liver diseases. There is a broad spectrum of complications encountered in early and late period after transplantation, and these contribute to significant morbidity and mortality. This review focuses on the most challenging area, that is, evaluation of liver allograft biopsies. A comprehensive approach based on clinic-pathologic features and tabulation of distinguishing features will guide pathologist to a correct approach. Various clinical conundrums and recent updates are covered.

   Role of Pathologist in Liver Transplantation   Top

Broadly, the roles played by the pathologist can be listed under pretransplant and posttransplant period [Table 1].[1],[2]

Spectrum of diseases in post-liver transplant setting

Complications in posttransplant period include: preservation/reperfusion alterations (PRI), functional impairment (e.g., cholestasis), allograft rejection, ischemic graft damage, recurrence of original disease, drug toxicity, biliary obstruction, vascular complications, opportunistic infections, de novo pathologies, and the whole gamut of liver diseases that we encounter in non-transplant context.[3]

The pathologist plays an instrumental role in the diagnosis, confirmation or refusal of clinical diagnosis, and narrowing down the differential diagnosis. Clinical situations in which liver allograft biopsy is often indicated are presented in [Table 2].[1],[4] Many of the causes require immediate diagnosis and treatment. Such biopsies need to be interpreted in conjunction with clinical information such as time course, previous episodes of rejection, posttransplant therapy, and any other medications, imaging results, underlying liver disease, and serology.[2] In addition, knowledge of characteristic histological findings of various complications, atypical and overlapping histological presentations, and time period of occurrence are crucial.

Early and late graft dysfunction

Early postoperative complications are often defined as complications occurring within the first 3 months after transplantation.[5] They are in general classified into surgical or nonsurgical causes. Surgical causes are further subdivided into vascular surgery (arterial, portal thrombosis, hepatic vein obstruction, and biliary complications). Nonsurgical causes are mainly related to problems of the graft itself (primary dysfunction/nonfunction, rejection, and drug-related liver toxicity or infections).[5],[6] Biopsy may be indicated in case of non-normalization or deteriorating liver function, rise after initial normalization, follow-up in cases of treated event, protocol time zero, or in case of any abnormalities found on imaging.[7]

Late graft dysfunction is due to complications occurring in period beyond 6 months [Table 3]. Late dysfunction also includes diabetes mellitus, systemic arterial hypertension, de novo neoplasia, and nephrotoxicity.[6],[8]

In the period of 3 to 6 months post-liver transplantation, most of the complications of early and late period can occur[1],[2] [Table 3].

Besides the time zones, histological patterns are very helpful in narrowing down the differential diagnosis [Table 4].

   Liver allograft rejection   Top

Histology remains the gold standard for diagnosis of rejection.[1] Three main patterns of rejection are hyperacute, acute, and chronic. They differ with respect to the time of occurrence, patho-physiological mechanisms, and clinico-pathological features.[9] Evaluation of liver allografts for rejection involves the recognition of diagnostic histopathological features, exclusion of non-rejection differentials, and identifying dominant issue in case of coexisting independent problems.

Acute rejection

Acute cell-mediated rejection (ACR) is the most common cause of early graft dysfunction, with incidence of 24% to 80%. However, ACR can occur even several years after transplant.[7] Early episodes usually resolve with antirejection treatment.[5]

ACR display characteristic morphological changes. Histological triad of portal inflammation, bile duct damage, and endotheliitis are seen; at least two of these three features are required for a diagnosis of ACR[1],[10],[11] [Figure 1].

Figure 1: Photomicrographs show ACR with triad of portal mixed inflammation, bile duct damage with degenerative changes, and portal vein endothelitis (a, 200x; b, 400x) and zone 3 central vein endothelitis with perivenular inflammation in severe acute rejection (c)

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Portal inflammation

The portal infiltrate ranges from mild to severe in severity, can involve a few or all sampled portal tract, and show mixed cell population comprising activated lymphocytes, eosinophils, macrophages, plasma cells, neutrophils, and eosinophils.

Bile duct injury

Bile ducts are infiltrated by inflammatory cells and exhibit evidence of epithelial injury in the form of pleomorphism in nuclear size and shape, uneven spacing of nuclei, cytoplasmic vacuolization, and focal basement membrane disruption.

Endothelial injury

Injury to the portal and/or terminal hepatic vein endothelium manifests as endothelialitis. Other features such as lifting/detachment of the endothelium, plump swollen appearance of endothelial cells, and/or nuclear atypia are also seen. More severe forms are associated with perivenular extension of inflammation leading to veno-occlusive lesions. These are often associated with recurrent episodes of rejection, less than normal response to increased IMS, and even an increased risk for CR.[10–13]

Grading of AR

ACR is graded in two ways. The first is global assessment based only on the severity of portal inflammation, and it is graded as indeterminate, mild, moderate, or severe.[11]

The more widely applied scoring system is based on the Banff 1997 document. This defines criteria for scoring ACR on a scale of 0 to 9. Portal inflammation, bile duct damage, and venous endotheliitis are semiquantitatively graded as 0 (absent) to 3 (severe). Total score determines whether rejection is indeterminate 1-2, Mild 3-4, moderate 5-6, or severe >6[11] [Table 5]. Cases with moderate or severe rejection are more likely to be associated with biochemical signs of graft dysfunction and have a greater risk of progression to CR.[1],[14]

Table 5: Banff 1997 criteria for scoring acute cellular rejection in liver allografts

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Important differentials of rejection are—PRI, early recurrence of hepatitis C virus infection (HCV), Epstein–Barr virus (EBV), drug toxicity, and surgical complications. Endotheliitis has a high diagnostic specificity for rejection. Mixed portal inflammation is another helpful feature in distinguishing ACR from other portal-based complications.[1]

Features distinguishing ACR from PRI are featured in [Table 6].[7] Steatosis, cholestasis, and hepatocellular ballooning favor preservation damage and perivenular necrosis suggests acute rejection.[2]

[Table 7] represents comparison of histopathological and clinical findings of ACR and HCV recurrence.[1],[15] However, combined damage is common and dominant cause needs to be identified.

Features that distinguish rejection from biliary obstruction/ascending cholangitis are illustrated in [Table 8][1],[7],[16] and from ischemic causes are in [Table 9].

Late acute rejection

Most ACR occur in the early posttransplant period; however, late-occurring ACR (Late acute rejection, LAR), upto several years posttransplant, is not uncommon. Most centers reduce IMS over 6 to 12 months to minimize opportunistic infection, malignancy, and drug toxicity; this might be the clinical trigger for LAR.[17] It has been variably defined as occurring more than 1-, 3-, or 6-months posttransplant, and affects 7% to 23% of transplant patients.[17],[18],[19],[20] However, early and late TCMR are not strictly time defined: considerable overlap exists, so strict separation can be difficult.

LAR shows “atypical” histopathological features, refractoriness to IMS and may progress to ductopenic rejection, graft loss, and morbidity.[7],[17],[18],[21] [Figure 2]. It is characterized by a predominantly mononuclear portal inflammatory infiltrate, less conspicuous inflammation of venular endothelium, less lymphocytic cholangitis, more significant interface activity, perivenular necro-inflammatory-type activity, lobular inflammation, and Veno-occlusive disease (VOD)-like changes.[7],[22] Comparison of LAR with early ACR and CR is demonstrated in [Table 10].[1],[7]

Figure 2: Late acute rejection showing portal tract changes of increased mononuclear cell inflammation, interface activity, bile duct damage with atrophic changes, and mild portal vein endothelitis (a-c); zone 3 changes of sinusoidal dilatation and congestion (VOD like changes), perivenulitis with prominent plasma cell rich inflammation (d-f)

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Due to chronic hepatitis like morphology, several entities need to be excluded: recurrent viral hepatitis, de novo autoimmune hepatitis (AIH), recurrent autoimmune hepatitis, and EBV-associated posttransplant lymphoproliferative disease (PTLD). Distinction of LAR from recurrent HCV, one of the most challenging diagnostic conundrums, has been covered in earlier section. T-cell and B-cell immunohistochemistry combined with the histomorphological features and EBV detection are helpful to rule out PTLD.[2] Presence of rejection histology, fluctuating/low serum tacrolimus levels, and absence of diagnostic histopathology and serology of AIH helps to exclude AIH.

Central perivenulitis and its differential diagnosis

Central perivenulitis (CPV) is an important feature of rejection and requires special mention. The term describes a spectrum of necroinflammatory changes involving terminal hepatic venules and the surrounding liver parenchyma.[23]

In the early posttransplant period, it usually occurs in association with typical portal tract features of acute rejection. However, in LAR, it may occur as an isolated lesion; this is called “isolated central perivenulitis.” It portends severe course in comparison to the cases which have portal tract rejection changes.[24],[25] Isolated CPV can be a result of several other causes, especially recurrent and de novo autoimmune hepatitis[1],[23] [Table 11].

Another issue with the diagnosis of LAR is the difficulty to apply the Banff Rejection activity index (RAI) score, particularly cases presenting with isolated CP or more severe centrilobular immune injury.[23] An alternative scheme for grading the extent of necrosis proposed by the Banff Working Group recommends descriptors [Table 12].[1],[23],[25]

Chronic rejection

CR classically presents as progressive graft dysfunction which can lead to graft failure. It can present as early as 3 to 6 months posttransplant but usually occurs later with an indolent course running over a period of several years.[1],[7],[13] The prevalence is declining and fewer than 2% of graft failure is due to CR.[1] Clinical history comprises prior (multiple) or ongoing cellular rejection episodes, LAR with CPV, problems in attaining satisfactory serum levels of IMS, or even de-novo, and presents with rising serum alkaline phosphatase levels.

Pathology

CR has two morphological characteristics: the loss of small bile ducts (ductopenia) and obliterative arteriopathy of medium- to large-sized arteries[26] [Figure 3].

Figure 3: Photomicrographs show chronic rejection-ductopenia (a), obliterative foamy arteriopathy (b), Parenchymal foam cells (c), perivenular hepatocanalicular bile, and sinusoidal congestion (d)

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Early CR shows inflammatory and degenerative changes in bile duct with senescence, “dysplastic-like” or atrophic appearance.[1],[27] Features may include: nuclear pleomorphism, high nucleocytoplasmic ratio, nuclear hyperchromasia, irregular spacing, cytoplasmic eosinophilia, and loss of polarity and detachment from the basement membrane. Portal tracts show minimal expansion or inflammation, and may have small ghost like appearance. There is no significant ductular proliferation, copper retention, or fibrosis.[7]

Ductopenia should be present in more than 50% of portal tracts. Adequacy of needle biopsy (minimum of seven fully sampled portal tracts) should be ascertained before rendering the diagnosis. However, duct loss can be patchy in distribution, thus more than 10 portal tracts is ideal. Cytokeratin 7 immunohistochemistry helps in the correct evaluation.[1],[7] Intermediate or large sized ducts may not be affected.[4]

Chronic ductopenic rejection is often applied to late CR. Early stage CR needs to be distinguished as it is potentially still reversible with the use of powerful immunosuppressive agents. [Table 13] enumerates the key features to distinguish early from late CR.[1],[7],[12],[23]

Arteriopathy of CR mainly involves intima of large and medium sized vessels, which are rarely present in the needle biopsy. Lesions range from intima foamy macrophage accumulation and fibromuscular thickening to transmural inflammatory infiltration and fibrous occlusion.[1],[2]

Other features often seen in CR include: changes in perivenular regions of the liver parenchyma such as perivenular bilirubinostasis, hepatocyte ballooning, hepatocellular necrosis, and sinusoidal foam cells.[7],[23] The 2000 Banff document describes staging system for CR, which requires assessment of a combination of clinical, radiological, laboratory, and histopathologic findings to reach the final diagnosis.[1],[9],[12]

Important differential diagnoses of CR are ischemic cholangiopathy and recurrent biliary disease (especially Primary sclerosing cholangitis (PSC))[1],[2] [Table 14].[1],[7] The most helpful diagnostic features are absence of ductular proliferation or significant periportal fibrosis in CR.[2] Imaging studies of the hepatic artery and/or biliary tract and correlation with clinical and microbiological data to exclude sepsis are also crucial. Also, other causes of vanishing duct syndrome such as drug toxicity should always be considered.

Antibody mediated rejection

Pure antibody mediated rejection (AMR) is relatively uncommon as liver allograft exhibits a well-documented AMR resistance.[28] Hyperacute rejection presents as graft dysfunction immediately after transplantation in a recipient. Main risk factor is an ABO-incompatible graft; other anti-donor antibodies are anti-lymphocyte antibodies, anti-endothelial antibodies, and antibodies that develop de novo following liver transplant surgery.[9] Histological features comprise complement-mediated thrombosis and chemoattraction of neutrophils in hepatic sinusoids and small vessels resulting in congestion and massive hemorrhagic necrosis.[1],[2]

Acute humoral rejection

Acute AMR usually occurs within the first several days/weeks after transplantation in highly sensitized recipients. The “signature” acute AMR microvascular pathology lesions are endothelial cell enlargement, capillary dilatation, leukocyte margination, neutrophilic exudation, congestion, and coagulative and hemorrhagic necrosis and edema.[28] Severe AMR can produce biliary strictures and veno occlusive type central vein lesions. Diagnosis of acute AMR should be based on strict criteria of graft dysfunction associated with compatible histological findings, presence of Donor specific antibodies (DSAs), and diffusely positive staining for C4d, as decision on the need of plasmapheresis is to be taken[28],[29] [Figure 4].

Figure 4: Acute antibody mediated rejection with necrosis, sinusoidal congestion and fibrin (a), portal capillaries with increased mononuclear cells and congestion and bile (b), C4d immunostaining in portal vessels and periportal sinusoids (c), and in portal stroma (d)

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Less severe cases may mimic biliary obstruction as they present with portal/periportal edema, neutrophil-rich inflammatory infiltration in portal tracts, and prominent ductular reaction.

C4d immunohistochemistry

Detection of microvascular complement deposition with C4d immunostaining, in correct histopathological context, is a reliable tissue marker of AMR.[27],[29],[30] In general, immunohistochemical demonstration of diffuse linear to granular C4d immunostaining (involving endothelium or stroma in >50% of portal tracts or sinusoids) suggests a significant component of antibody-mediated graft damage.[29],[31] C4d labelling can be seen in arterial elastic lamina, portal and perivenular elastic fibers, in necrotic and steatotic hepatocytes, and in the areas of sinusoidal fibrosis.[1],[28],[31]

Although C4d staining documented in recurrence of hepatitis B and C, plasma cell hepatitis and biliary obstruction are less widespread and intense than those associated with AMR.[28], [29],[30],[32]

Guidelines and consensus criteria for the diagnosis of liver allograft AMR was published in 2016 comprehensive update of the Banff working group.[28] C4d immunohistochemistry is graded on a scale of 0 to 3 [Table 15].[28] Characteristic microvascular pathology of acute AMR is scored according to [Table 16] [28] and [Table 17].[28]

Table 15: Component lesion scoring for acute AMR [C4d-(immune)-score (formalin-fixed, paraffin-embedded]

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Table 16: Component lesion scoring for acute AMR [h-(histopathology)-score]

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Chronic antibody mediated rejection

Chronic AMR histopathological lesions can be seen in allograft biopsies of long-term follow-up of pediatric recipients, in suboptimally, immunosuppressed recipients, as part of IMS weaning studies or protocol biopsy[28] [Table 18].[28]

Plasma cell-rich rejection (PCRR)

AMR is often associated with superimposed TCMR. Standard criteria for AMR and TCMR should be used in such mixed AMR/TCMR episodes. In late graft dysfunction, when AIH is not an original disease, mixed TCMR/AMR overlapping with autoimmunity is designated as “plasma cell-rich rejection (PCRR).”[28]

PCRR, contrary to AIH, shows more prevalent and severe lymphocytic cholangitis, IgG4 + plasma cell overrepresentation, more aggressive plasma cell-rich CPV, DSA positivity, portal microvascular C4d deposition, coexistent typical TCMR or CR features, along with other features compatible with rejection.

Dominance of plasma cells can be seen in several other conditions such as: de novo AIH, recurrent AIH, recurrent ACR, recurrent HCV infection, or on therapy, in which it is also known as plasma cell hepatitis.[28],[33],[34]

   Recurrence of primary disease   Top

Disease recurrence represents the major cause of graft dysfunction in long-term survivors.[35] The frequency of disease recurrence after liver transplantation is highly influenced by the etiology of the primary liver disease; for example, hepatitis B and C almost universally recur[35],[36],[37] [Table 19].[2] Primary biliary cirrhosis (PBC), PSC, AIH, alcoholic liver disease, nonalcoholic fatty liver disease (NAFLD) also recurs.[38],[39],[40] Recurrence of hepatocellular carcinoma is based on stage of disease, other risk factors, such as microscopic vascular invasion and multiple tumours.[41],[42] In contrast, the majority of pediatric transplant operations are carried out for nonrecurring diseases such as biliary atresia and various metabolic disorders including α1-antitrypsin disease, Wilson disease, and cystic fibrosis—which are cured by transplant.[7]

Recurrent diseases such as AIH and PSC in children show histological features very similar to those in the adult population.[1] PBC may show features of overlap of AIH-PBC in allograft recurrence [Figure 5] and [Figure 6]. Recurrent chronic HBV infection has a more aggressive course with more rapid progression of fibrosis and more severe activity.[43] Pathological features of HBV infection in liver allograft are similar to those seen in non-allograft livers. Recurrence of HCV manifests with portal inflammation, interface activity, random lobular inflammation, and apoptosis. In coexisting rejection and HCV recurrence, identifying the dominant cause is important as recurrent HCV benefits from reduction in IMS, whereas ACR is managed by increased IMS.[4]

Figure 5: Photomicrographs of porta transplant recurrence—Overlap of PBC (portal granulomatous inflammation) with AIH (zone 3 plasma cells) (a and b); Alcoholic hepatitis combined with acute rejection (c and d)

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Figure 6: Photomicrographs of porta transplant recurrence—Hepatocellular carcinoma with P CEA immunostaining (a and b); HCV recurrence (c), and HBV recurrence with ground glass appearance (d)

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Hepatitis E virus (HEV) infection may also lead to late graft inflammation and chronic hepatitis in the setting of IMS; In a small number of cases, it may even lead to the development of severe fibrosis or cirrhosis.[7],[44]

Particularly important is the awareness of atypical pattern of recurrence of viral disease “Fibrosing cholestatic hepatitis” (FCH). This mainly presents during the first few months after transplantation, when levels of IMS are highest. FCH is characterized by diffuse hepatocellular swelling, cholestasis, prominent ductular reaction, and rapidly advancing portal, periportal, and sub-sinusoidal fibrosis, but lack of significant inflammatory infiltrate. The swollen hepatocytes often show cytoplasmic and nuclear immunoreactivity for HBcAg as indicative of viral replication.[7],[45]

   Infections and Sepsis   Top

Infections are the most common cause of death in the first 3 years after liver transplant.[46] More than half of transplanted patients have at least one infectious complication, with over 80% of infections occurring within the first 6 months following transplant.[47]

In addition to the common spectrum of complications seen after major abdominal surgery, IMS-related opportunistic infections represent a major problem after liver transplantation. Cytomegalovirus (CMV) infection, the most frequent viral agent involving liver allografts, frequently manifests between 1 and 3 months posttransplant. Typical histology includes micro abscess formation and characteristic viral inclusions.[2],[6] Herpes simplex virus hepatitis is represented by acute necrotizing hepatitis with characteristic eosinophilic nuclear inclusions (Cowdry type A),[6] and adenoviral infections with confluent hemorrhagic necroses and diagnostic smudge cells.[48] EBV infections are associated with the development of PTLD. PTLD occurs in 4% of recipients.[2],[49] Liver transplant patients are also particularly susceptible to fungal infections, predominantly candida, aspergillus, and cryptococcal infection.[2] These are mainly seen in the association with ischemic bile duct necrosis, but may involve the liver in systemic infections.[6]

Bacterial infections are quite common. Sepsis is associated with a characteristic histological picture known as “cholangitislenta,” which consists of cholestasis and cholangiolar proliferation with prominent bile plugs at the periphery of portal tracts. Ascending cholangitis shows a pattern of luminal neutrophils as well as ductular proliferation, edema, and rounding of portal tracts.[2]

Clinical and laboratory information is very important because long-standing dysfunction may show histological overlap with rejection and recurrence of biliary pathologies.[Figure 7]

Figure 7: Photomicrographs of other complications–sepsis (cholangitis lenta) (a), Acute hepatitis (b), Drug induced liver injury with hepatocanalicularbilirubinostasis (c), Hepatic vein outflow tract obstruction with zone 3 sinusoidal congestion (d), Preservation-Reperfusion injury (e), and biliary obstruction with portal mixed inflammation, ductular bile plugs, and biliary fibrosis (f)

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   New onset de novo diseases   Top

The term “de novo disease” is used to describe patients who are transplanted for one type of primary liver disease and subsequently develop features suggesting a different primary liver disease.[1]

This applies to viral infections (hepatitis B and C), AIH, and NAFLD. Histological features are generally similar to those seen in recurrent disease.[1]

New onset of AIH occurs in high frequency in children (5% to 10%) compared with adults (1% to 2%); possibly related to immunosuppressive drugs interfering with normal T-cell maturation.[1] Diagnosis of de novo AIH is based on a combination of the classical histopathological features and autoimmune serology.[7] Histological assessment is essential as serum markers of AIH may not be reliable due to immunosuppressants.[4] Preponderance of plasma cells mandates exclusion of other causes, especially PCRR.[1],[23] Correct diagnosis is important, as unlike AR, de novo AIH requires steroid treatment for extended duration[4] [Figure 8].

Figure 8: De novo complications–Steatohepatitis (a), AIH (b), and hepatic structural abnormalities–Nodular regenerative hyperplasia (c and d)

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De novo nonalcoholic fatty liver disease

Obesity is a frequent complication in transplanted patients with a prevalence of 15% to 40% 1-year posttransplantation.[47] Transplant recipients are at risk for developing a number of features of the metabolic syndrome, such as diabetes mellitus, weight gain, hypertension, hyperlipidemia, and NAFLD.

Idiopathic chronic hepatitis

Unexplained chronic hepatitis in the adult liver allograft recipient is not uncommon. The incidence ranges from 10% to 50% in different series.[7] Biopsies display portal mononuclear inflammatory infiltrate, interface hepatitis along with lobular inflammation, hepatocyte necrosis, or apoptosis.

   Preservation–reperfusion injury   Top

PRI refers to tissue damage causing graft dysfunction immediately after transplantation. Liver preservation and subsequent reperfusion leads to sinusoidal endothelial cell damage, cellular apoptosis, and cell death with ischemic necrosis.[7],[50]

Changes related to PRI are generally mild, but may evolve to more severe lesions during the first 1 to 2 weeks. Histological features encompass: microvesicular steatosis, rounding-up of hepatocyte cytoplasm with detachment from adjacent hepatocytes, and hepatocellular swelling, polymorph aggregates, and cholangiolar cholestasis in mild injury. Zonal or confluent coagulative necrosis, sometimes with periportal or bridging necrosis, and severe neutrophilic exudation may be seen in more severe injury.[1],[7],[51],[52]

Clinico-pathologic correlation is required to exclude other causes of early graft dysfunction, particularly sepsis, biliary obstruction, AMR, ACR, cholestatic hepatitis, and small size donor grafts.[7],[53] Biopsy examination is especially helpful to exclude rejection; although, PRI and rejection can occur simultaneously.

Biliary complications and Hepatic artery thrombosis

The three main vascular anastomoses in the liver allograft are hepatic artery, portal vein, and vena cava, they can be involved by technical complications (e.g., anastomotic stricture or kinking) or by thrombosis, resulting in vascular occlusion.[1],[54]

The sole source of vascular supply to the allograft biliary system is the hepatic artery. Thus, integrity of arterial flow is of paramount importance. Vascular complications are more frequent in children and in recipients of segmental liver grafts. Hepatic artery thrombosis (HAT) occurs in 3% to 9% of patients who undergo LT.[55] Ischemic bile duct necrosis, typically affecting large intrahepatic bile ducts, along with strictures, and bile leaks, is an important complication of later HAT.[56–60]

Allograft biopsy findings range from completely normal to marked centrilobular hepatocyte swelling, later centrilobular hepatocellular atrophy, sinusoidal widening, ductular reaction, with or without bile plugs, acute cholangiolitis, and frank coagulative necrosis.[7],[61]

   Biliary Complications   Top

Biliary complications, which remain an important complication of liver transplantation, include leaks, strictures, casts, sludge, or stones and have an overall prevalence ranging from 10% to 25%.[1],[2],[62],[63],[64]

Bile duct stricture may be anastomotic or non-anastomotic. Most anastomotic strictures are diagnosed radiologically; therefore, liver biopsy has a limited role. Characteristic biopsy features are portal tract changes in the form of edema, ductular reaction, and neutrophil-rich inflammatory infiltration, along with centrilobular hepatocanalicular cholestasis. Small clusters of neutrophils throughout the lobules may also be commonly seen.

Non-anastomotic strictures tend to occur later after transplantation, are less responsible to treatment, are generally progressive, and adversely impact graft and patient survival. Ischemia-induced bile duct lesions (ischemic cholangitis/ischemic cholangiopathy) can occur upto 10%.[2],[65] Ischemic cholangitis manifests as segmental strictures and occasionally as secondary infection of the biliary system.[2],[65],[66] Biopsy displays chronic portal inflammation and biliary epithelial cell senescence with atrophic/atypical appearance of biliary epithelium.[1],[2],[7],[64] Other conditions that need to be excluded are CR, AMR, PRI, and recurrence of primary disease, such as PSC or AIH, or CMV infection.[2],[66],[67]

   Drug toxicity   Top

Drug-induced liver injury can mimic many patterns of transplant-related and non-transplant-related liver pathology.[7] In case of nonspecific histopathological findings, such as centrilobular cholestasis, focal feathery degeneration of hepatocytes, peliosis, and sinusoidal dilatation, drug toxicity should be considered in the absence of other causes.[7],[68],[69] Immunosuppressive therapy exhibits hepatotoxic potential. Tacrolimus-related liver toxicity may manifest as nodular hyperplasia or perivenular necroses in allograft biopsy.[2],[70]

Azathioprine toxicity may result in vascular and endothelial damage as well as hepatitis patterns.[1],[7] Cyclosporin A can cause hepatocellular ballooning, cholestasis, nodular regenerative hyperplasia (NRH), and single cell necrosis. Corticosteroids are associated with periportal steatosis and NRH.[4] Antibiotics may be associated with hepatitis, cholestatic or mixed liver injury, and rarely vanishing of bile ducts.[7] But, in general, severe liver damage is rarely attributable to drug toxicity alone in the posttransplant setting.[2],[69]

Hepatic structural abnormalities

Hepatic structural abnormalities are observed in 20% to 30% of biopsies, usually in late posttransplant biopsies. Biopsy shows sinusoidal dilatation and congestion, perisinusoidal fibrosis, and NRH. Identification of NRH is facilitated by reticulin staining.[25],[71],[72] Drug toxicity (IMS) and correlation with C4d and DSA to exclude AMR are essential.

IMS weaning trials require biopsy-based evidence to decide whether patient is likely to benefit from reduction of IMS, for example, in pediatric recipients or renal impairment due to therapy-related toxicity. Histological features assessed are outlined in [Table 20].[28]

Table 20: Histological criteria for decision of minimization of IMS therapy

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   Conclusion/Summary   Top

In summary, this article is intended as a guide to systematic approach of liver allograft biopsy. Determining the correct diagnosis, ascertaining the dominant disease, and monitoring treatment response are some of the most significant roles played by a pathologist. Meticulous assessment of histomorphological patterns, combined with proper knowledge of pertinent clinical information, and the time period posttransplantation, aids to resolve posttransplant clinical dilemmas.

Acknowledgments

Prof (Dr) SK Sarin, Senior Professor (Dept. of Hepatology) & Director, ILBS, Delhi, & Dr Gayatri Ramakrishna, Professor, Department of Molecular & Cellular Medicine, ILBS, Delhi.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 

   References   Top


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Correspondence Address:
Archana Rastogi
Department of Pathology, Institute of Liver and Biliary Sciences (ILBS), D-1, Vasant Kunj, New Delhi – 110 070
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_1090_21

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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
 
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10], [Table 11], [Table 12], [Table 13], [Table 14], [Table 15], [Table 16], [Table 17], [Table 18], [Table 19], [Table 20]

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