Meroanencephaly: Pathology and Prenatal Diagnosis

Abstract

Meroanencephaly is a rare form of anencephaly characterized by malformed cranial bones and a median cranial defect, through which protrudes abnormal tissue, called the area cerebrovasculosa. Area cerebrovasculosa denotes abnormal spongy, vascular tissue admixed with glial tissue ranging from a thin membrane to a large pseudoencephalic mass simulating 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 completely absent, and (3) craniorachischisis, the most severe, where area cerebrovasculosa and area medullovasculosa fill both cranial defects and the spinal column. In meroanencephaly, there is a median defect present, through which protrudes the area cerebrovasculosa. We present 3 cases of meroanencephaly diagnosed prenatally, along with histopathologic analysis. One case showed ectoptic glial tissue in the lung and adrenal 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 should be included in the differential for protruding anterior cranial masses.

Newborn with meroanencephaly: Surviving all odds

“…Anencephaly is clinically described into three types – meroanencephaly, holoanencephaly, and craniorachischisis. [1] Meroanencephaly is the classic form which presents as a lack of cranial vault bones and exposed dorsal undifferentiated dorsal neural tissue. [1] Usually, cerebral hemispheres fail to develop and only brainstem and some parts of midbrain may be present.…”

“…[1] Meroanencephaly is the classic form which presents as a lack of cranial vault bones and exposed dorsal undifferentiated dorsal neural tissue. [1] Usually, cerebral hemispheres fail to develop and only brainstem and some parts of midbrain may be present. Holoanencephaly is the more severe form in which lesion extends to hindbrain also.…”

Reduced expression of CD99 and functional disturbance in anencephalic cortical thymocytes

“…It is divided into two subtypes: mero-anencephaly (the presence of rudimentary brain tissues and partial formation of the cranium) and holoanencephaly (no cranial vault) [18]; both result from a failure of neural tube closure. This failure appears to be multifactorial, arising from the combined effects of several genetic abnormalities and environmental hazards [16].…”