MEROANENCEPHALY - PATHOLOGY AND PRENATAL-DIAGNOSIS

Meroanencephaly is a rare form of anencephaly characterized by malform ed cranial bones and a median cranial defect, through which protrudes abnormal tissue, called the area cerebrovasculosa. Area cerebrovasculo sa denotes abnormal spongy, vascular tissue admixed with glial tissue ranging from a thin membrane to a large pseudoencephalic mass simulati ng cerebral tissue, that is composed of connective tissue, hemorrhagic vascular channels, glial nodules, and disorganized choroid plexuses. There are three types of anencephaly: (1) meroanencephaly, where there is rudimentary brain tissue and partial formation of the cranium; (2) holoanencephaly, the most common type, in which the brain is complete ly absent, and (3) craniorachischisis, the most severe, where area cer ebrovasculosa and area medullovasculosa fill both cranial defects and the spinal column. In meroanencephaly, there is a median defect presen t, through which protrudes the area cerebrovasculosa. We present 3 cas es of meroanencephaly diagnosed prenatally, along with histopathologic analysis. One case showed ectoptic glial tissue in the lung and adren al medullary hyperplasia. Two cases were diagnosed in the early second trimester by ultrasound scanning. Meroanencephaly may be mistaken for encephalocele both at the bedside exam and sonographically, and shoul d be included in the differential for protruding anterior cranial mass es.