This section of the tutorial will identify a number of non-rejection findings that can be seen in these biopsy samples. Some of these findings are common, while some are exceedingly rare. Many of these findings can be easily confused with rejection and it is critical to not overcall rejection based on these histologic patterns.
Endomyocardial biopsies in ~50% of patients with cardiac allografts may have focal, dense endocardial collections of lymphocytes that can extend into adjacent myocardium. These common changes are termed Quilty effect (formerly Quilty lesion, named after the first patient in whom they were described). These lesions consist of a mix of B lymphocytes and T lymphocytes and occasionally dendritic cells. Small vascular channels (capillaries) can be noted within some of the inflammatory infiltrates.
The pathogenesis of the Quilty effect is not known, but hypotheses have included cyclosporine-based immunosuppressive regimens, idiosyncratic responses to cyclosporine A, and concomitant Epstein-Barr virus infection. The Quilty effect is not seen in hearts from patients who received cyclosporine A for other solid organ transplants (i.e. kidney, liver). Many groups have investigated the relationship between Quilty effect and grade of cellular rejection, viral infection, AMR, and/or development of graft vasculopathy. Studies both supporting and refuting associations with these other findings make this a continuing area of discovery. Overall, there is not a consensus of an association between Quilty effect and any key histopathologic or outcome data.
Quilty effect can be confined to the endocardium, or it can extend into adjacent myocardium. Some large Quilty effects do interdigitate amongst underlying myocytes resulting in peri-Quilty myocyte injury. This mimicker of rejection is believed to be a frequent etiology of the the ISHLT-1990 grade 2 lesions. In this scenario, a distinction from acute cellular rejection must be made. This may require multiple sections through the tissue block to establish that it has an endocardial component (although acute cellular rejection can also have an endocardial distribution). When present, small vessels or capillaries within the inflammatory infiltrate can be very helpful in recognizing Quilty effect. Additionally, the stroma among myocytes in Quilty effect may appear more fibrous.
In some cases, lymphocyte typing by immunoperoxidase techniques may be required, in which case Quilty will have a mixture of B and T lymphocytes and macrophages, unlike acute cellular rejection in which T cells predominate. A CD21 stain can also be used. When positive, it is a strong marker of Quilty effect. A negative CD21 is not prognostic.
If Quilty effect is seen within other pieces in the biopsy, it may be more likely that a focus of inflammation within the myocardium is also Quilty, although acute cellular rejection cannot be totally excluded on that basis alone. As a Quilty effect heals, small scars simulating previous biopsy sites can be seen. The scars with Quilty tend to have more even, linear borders in contrast to scars from previous biopsies that have a more uneven interface.
Ischemic (Peri-transplant) injury
Ischemic injury (peri-transplant injury) is usually noted in the biopsies taken during the first 6 weeks after transplant but can be present for up to 3 months. This process can be difficult to distinguish from acute cellular rejection. Due to the ischemia of the heart as it is moved from the donor to the recipient, some variable number of myocytes will die from this process. Myocyte death is generally found in clusters (large or small). In the inital biopsy, myocyte death may be very subtle with only increased myocyte cytoplasmic eosinophilia and anucleation being apparent. Dead myocytes will stain strongly for C4d by immunohistochemistry or immunofluorescence. This should not be confused with antibody mediated rejection. Late myocyte death can be seen, but can be distinguised from acute cellular rejection by a lack of lymphocytic infiltrate. Due to the strong immunosuppression, inflammation may not be observed early in the process.
Generally 2-4 weeks after transplant, the maximal inflammation process is present. This is primarily a macrophage-mediated response. This inflammation can be extensive and associated with myocyte injury. The key feature to distinguish this from acute cellular rejection is a mixed inflammatory infiltrate versus a lymphocyte-rich infiltrate. Ischemic injury can also have a "dirty" interstitial background. When there is both acute cellular rejection and ischemic injury in the same biopsy, making a distinction can be difficult. It is very easy to overcall rejection at this time point due to the dual processes, but since most patients will return for a repeat biopsy within a week or two, caution is advised.
After the first month, most ischemic injury looks like a typical resolving small infarction with pigment-laden macrophages, loose connective tissue and a regional loss of myocytes. This is not as easily confused with acute cellular rejection but it is difficult to distinguish from a previous biopsy site.
Biopsy site changes & thrombus
Due to the architecture of the right ventricle, it is not uncommon for the bioptome to be guided to the same or similar locations and injury from previous biopsies in cardiac transplant patients should be recognized. The appearance of a previous biopsy site will vary depending upon the interval between the current and previous biopsies. A recent biopsy may result in a focal endomyocardial defect with an overlying fibrin-platelet or organizing thrombus and some inflammatory cells (macrophages, T, and B cells). During the reparative stage, it may consist of granulation tissue, and eventually a focal endocardial scar will be seen. The myocytes adjacent to a scar will have focal disorganization and/or irregular hypertrophy. They may appear as myocyte disarray. In situations in which patients undergo repeated endomyocardial biopsies, such as cardiac transplantation, the chance of obtaining a previous biopsy has been reported to range from one in seven up to nearly 70% of biopsies.
Inflammation in areas of biopsy site changes is not acute cellular rejection and should not be graded as such. Thus a biopsy may have no rejection (0R) but have an area of inflammation associated with a biopsy site.
In some individuals, collections of lymphocytes filling a lymphatic channel appear. The etiology of this finding is unknown. This finding is not related to acute cellular rejection and does not need to be reported.
Adipose tissue and mesothelial cells
Adipose tissue is a normal, minor component of the myocardium, often appearing adjacent to larger arterioles. Occasionally, larger collections of adipocytes, or frank adipose tissue is seen in biopsy samples. Frequently, they will have small portions of non-compact myocardium attached. These samples come from free wall of right ventricle and, apart from not being suitable for assessment of acute rejection by virtue of their site, they have little significance. Occasionally the presence of adipose is more ominous. When there are strips of mesothelium either attached to the fat or found separately in the block, or when small nerves are noted within the fat, this suggests the source of the tissue is the epicardial fat. This indicates perforation of the right ventricle and the clinician should be contacted urgently to be informed of this fact because of the risk of significant hemopericardium. In most heart transplant patients the pericardium has adhered to the heart, making the risk of fatal hemopericardium significantly reduced relative to a similar finding in a native heart biopsy.
Myocyte calcification is an extremely rare finding at heart transplant. The etiology is believed to be transient hypercalcemia during the transplantation event resulting in metastatic calcification of myocytes. It can also be observed in old biopsy sites. Calcification is more likely to occur in the setting of acute or chronic renal failure. Histologically this appears as calcification of myocytes either individually or in clusters. Increased fibrosis may occur in these sites, but inflammation is not typical. Although extensive cardiac calcification may negatively affect cardiac function, it is not associated with acute cellular rejection.
Some disease processes that result in heart failure have been reported to recur in the transplanted heart. These include sarcoidosis, giant cell myocarditis, amyloidosis, Chagas and light chain deposition disease. A pathologist should be aware of any of these reasons why a patient was transplanted and be aware of a return in these diseases. Sarcoidosis and giant cell myocarditis may both particularly mimick acute cellular rejection.
It is very unusual to identify an infection in an endomyocardial biopsy, despite transplant recipients being at elevated risk of infection due to immunosuppresion. Cytomegalovirus (CMV) has been reported in heart biopsies, however CMV status is usually better identified by serology (only if the recipient was initially CMV negative prior to transplantation) or in other tissues (ex. esophagus). However, the presence of viral inclusions may be identified on the biopsy material. A CMV or other viral immunohistochemical stain can then be obtained. If infection is present, that information should be conveyed to the clinician but should not be confused with acute cellular rejection. Toxoplasmosis may also be seen in the transplanted heart. Bradyzoites can fill myocytes without a significant inflammatory reaction. This can also be detected by immunohistochemistry.
Post transplant lymphoproliferative disorder (PTLD)
Although post transplant lymphoproliferative disorder (PTLD) occurs in a fairly high percentage (up to 6%) of transplant patients, it is extremely unusual to make that diagnosis on endomyocardial biopsy. Histologically, when it appears, it will typically be sheets of B lymphocytes mimicking acute cellular rejection. These cases are usually EBV positive, so performing EBV in situ hybridization and B cell immunohistochemistry (CD20) in cases suspicious for PTLD is warranted. Also, this diagnosis can sometimes be entertained when a patient fails to respond to what is presumed to be acute cellular rejection. The presence of a significant number of plasma cells in a biopsy is unusual and can be evaluated for a plasmacytoid PTLD. Rarely T cell lymphomas also cause PTLD.
Small clusters of foreign body giant cells may be seen in endocardium in recipients who have had repeated biopsies. They may contain refractile material, held to be probably fragments of cotton fibre from gauze used to wipe the bioptome between biopsies.
Tricuspid Valve Fragments and Liver Fragments
About 12% of transplant recipients develop a tricuspid murmur in the years post-transplant. The most common cause of post transplant tricuspid regurgitation is congestive heart failure, annular dilatation or pulmonary hypertension. Rarely, this is because of accidental tearing of the valve cusp or snagging of a chorda by the bioptome as it crosses the tricuspid valve. If pieces of either are seen in the biopsy sample the clinician should be informed. Although biopsy of chordal fragments are usually well tolerated, a flail valve due to a big enough defect may affect graft function significantly. A valve or chord fragment will be essentially be a narrow band of fibrous tissue with elastic fibers aligned horizontally with the long axis of the material. Endothelial cells may be seen on both sides, unlike a piece of thickened endocardium, although this distinction can be difficult to make.
Extremely rarely, the bioptome can pass from the superior vena cava into the inferior vena cava, without clinical appreciation, and sampling can be taken from the liver instead of the heart. Thus a piece of liver on a biopsy slide can come from the patient or from a possible contaminant ("tissue pickup") in the clinical laboratory from poor technique.
The information on the Society for Cardiovascular Pathology's Web Site is provided with the understanding that the Society
is not rendering medical advice, or recommendations. You should not rely on any information in the text files, messages,
bulletin boards or articles on these pages to replace consultations with qualified health care professionals to meet your individual medical needs.
The information on the Society for Cardiovascular Pathology's Web Site is provided with the understanding that the Society is not rendering medical advice, or recommendations. You should not rely on any information in the text files, messages, bulletin boards or articles on these pages to replace consultations with qualified health care professionals to meet your individual medical needs.