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Metastases are the most common malignant tumors of the liver. In the files of the Institute of Pathology of the University of Cologne 12,161 liver tissue cases are registered. Of them, 1,357 cases (11.2%) showed tumors or tumor like masses. Liver metastases of solid tumors were the largest group of the neoplasias with 611 cases (5.0%) followed by hepatocellular carcinoma (380 cases; 3.1%). Other entities were rare and include cholangiolar carcinoma (0.5%), vascular tumors (0.4%), lymphomas (0.4%), focal nodular hyperplasias (0.36%) and liver cell adenomas (0.23%). Adenocarcinomaa are the largest group of metastases with 400 cases (65.5%). 48.2% of this group were metastases of colorectal cancer, 13.5% of pancreatic cancer, 13% of breast cancer, 6.2% of gastric cancer, 4.5% of lung cancer and 3.7% of esophageal cancer. Neuroendocrine carcinomas are the second largest group with 16% of liver filiae. Other entities were rarely found. Metastases in cirrhotic livers are seldom. The gross findings, the histology, the differential diagnosis including immunohistochemistry and the value of the liver biopsy is discussed.

Extramedullary myeloblastic tumors, so-called myelosarcomas (granulocytic sarcomas, chloromas) have been reported only sporadically in the pertinent literature which reflects their rather infrequent occurrence. These lesions may accompany the initial manifestation or signal relapse of acute myeloid leukemia (AML) or coincide with blastic transformation of a chronic myeloproliferative disorder. However, even more rarely, primary myelosarcomas may precede AML by months or years or may be associated with myelodysplastic syndromes (MDS) that never progress to manifest leukemia. In a retrospective evaluation a clinicopathological study on these latter two variants of isolated extramedullary manifestations of AML was performed to elucidate certain aspects of site involvement and histopathology by application of enzyme and immunohistochemistry. For this reason, we selected 6 patients presenting with a myelosarcoma in combination with MDS and 12 patients revealing only uncharacteristic reactive changes of the bone marrow. Of these patients 8 developed AML following an observation time of up to 2 years. Focal leukemic infiltrates were most often localized in the skin ( n=4), oral mucosa ( n=4), lymph nodes ( n=3), gastrointestinal tract ( n=3) or pleura and retroperitoneum ( n=3 each). Myelosarcomas were usually regarded by the clinicians as putative malignant lymphomas unless further evaluation, especially involving chloroacetate esterase reactions as well as immunostaining with a panel of antibodies reactive with lysozyme, myeloperoxidase, CD68, CD43, CD56, CD117 and CD34 proved their true nature. Although at that time bone marrow findings were inconclusive, a straightforward diagnosis was reached by considering the possibility of a (primary) myelosarcoma in these patients.

Skeinoid fibers are interstitial collections of a pathological collagen, most often seen in gastrointestinal stromal tumors. They were first described in 1991. We report two cases of intestinal stromal tumors, one in an exceptionally young patient with excessive skeinoid fiber deposition. The microscopic as well as the ultrastructural findings of skeinoid fibers are demonstrated and their role is discussed considering the newest literature.

Histological evaluation of liver biopsies is the gold standard for assessing the severity of liver disease in chronic hepatitis C. In conjunction with anamnestic and serological data, it provides critical information regarding prognosis and therapeutic consequences. Grading of the necroinflammatory activity and staging of the manifested fibrosis according to well-established scoring systems are the essential parameters of the histopathological report. The frequency of chronic hepatitis C necessitates awareness of coinciding liver damage by nutritional or drug toxicity, bile duct diseases, and hereditary hemochromatosis. Detection of hepatitis C virus (HCV) RNA directly from the formalin fixed, paraffin-embedded biopsy specimen is highly sensitive and offers help in cases of equivocal results of serological testing for HCV.

Well-differentiated hepatocellular tumors represent a difficult diagnostic problem in hepatopathology with rising clinical impact. The differential diagnosis mainly includes well-differentiated hepatocellular carcinoma (HCC) and its premalignant precursor lesion, the dysplastic nodule (DN), in addition to multiacinar regenerative nodule as well as hepatocellular adenoma (LCA) and focal nodular hyperplasia (FNH). Optimized diagnosis of these lesions is based on exact histomorphological analysis, a close interdisciplinary cooperation as well as good clinical and anamnestic information. Histopathological differential diagnosis requires the search for specific characteristics and detailed analyses of the subtle cytological differences, the histoarchitecture, and also the surrounding nontumorous liver tissue. Special techniques may be helpful in selected cases but currently are of limited importance.

The evaluation of a liver biopsy in chronic hepatitis should make a statement on the etiology and report the degree of activity and stage of the disease. The category of so called seronegative chronic hepatitis may include cases of chronic hepatitis C or infection with other viruses such as the Epstein-Barr virus (EBV) and cytomegalovirus (CMV), cases of marker-negative autoimmune hepatitis as well as drug-induced injury and Wilson's disease in younger patients. In order to establish the diagnosis, sensitive techniques of molecular biology should be applied as well as copper staining by histochemistry. Exact and detailed histopathologic analysis can reveal certain features of autoimmune hepatitis or drug injury.