Abnormal choroid plexus morphology Choroid plexus carcinoma Intraventricular papillary neoplasm derived from choroid plexus epithelium. Plexus tumors are most common in the lateral and fourth ventricles; while 80% of lateral ventricle tumors present in children, fourth ventricle tumors are evenly distributed in all age groups. Clinically, choroid plexus tumors tend to cause hydrocephalus and increased intracranial pressure. Histologically, choroid plexus papillomas correspond to WHO grade I, choroid plexus carcinomas to WHO grade III. UMLS:C0431109 SNOMEDCT_US:88252006 Malignant neoplasm of the central nervous system