Pseudoneoplasms in ectothermic animals.

Gross and cytologic similarities between certain non-neoplastic conditions and neoplasms in lower animals including fish, amphibians, and reptiles have invited misinterpretations and contested interpretations. Major categories of pseudo-neoplasms, illustrated by specific examples from material accessioned into the Registry of Tumors in Lower Animals, include infections by foreign organisms which resemble host cells (algal protothecosis and amebic pseudotumors); unusual normal conditions [giant islets of endocrine pancreas (Brockmann bodies) in liver, atypical sites of hematopoietic tissue]; nonparasitic hyperplasia (goiter, ectopic thyroid, erythroblastic proliferation suggestive of pernicious anemia, adenofibrosis); parasite-induced hyperplasia (trematode-induced fibrosis, ciliate-induced monocytic leukocytosis, trematode-induced melanosis, glochidiosis); dysmorphogenesis (teratoid anomalies); virus-induced hypertrophy (lymphocystis); and reactive lesions (metaplasia, regeneration, inflammation).