Adenomatoid Tumor: A Review of Pathology With Focus on Unusual Presentations and Sites, Histogenesis, Differential Diagnosis, and Molecular and Clinical Aspects With a Historic Overview of Its Description

Adenomatoid tumors have been described almost a century ago, and their nature has been the subject of debate for decades. They are tumors of mesothelial origin usually involving the uterus, the Fallopian tubes, and the paratesticular region. Adenomatoid tumors of the adrenal gland, the liver, the extragenital peritoneum, the pleura, and the mediastinum have been rarely reported. They are usually small incidental findings, but large, multicystic and papillary tumors, as well as multiple tumors have been described. Their pathogenesis is related to immunosuppression and to TRAF7 mutations. Despite being benign tumors, there are several macroscopic or clinical aspects that could raise diagnostic difficulties. The aim of this review was to describe the microscopic and macroscopic aspects of adenomatoid tumor with a special focus on its differential diagnosis and pathogenesis and the possible link of adenomatoid tumor with other mesothelial lesions, such as the well-differentiated papillary mesothelioma and the benign multicystic mesothelioma, also known as multilocular peritoneal cysts.

[Adenomatoid tumors in myometrium (author's transl)]

In 6000 cases of hysterectomy nine adenomatoid tumors of myometrium were observed. Macroscopically, the adenomatoid tumour appears as a round or ovoid mass of grey or whitegrey colour about the size of a hazel-nut. Microscopically, four types are distinguished: solid, angiomatoid, macrotubular and mixed types. The cytoplasma of the cells tends to be vacuolated, the glandlike spaces being probably derived by confluence of these vacuoles. The interstitial tissue contains cells of the same type and often lymphocytes. Several hypotheses concerning the histogenesis of adenomatoid tumors are reviewed. The adenomatoid tumor is more frequent in the myometrium than it has been hitherto known. Probably the tumor is often misinterpreted as leiomyoma of the uterus on the basis of macroscopical appearance only.