Glossary in Congenital Malformations

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#Pachygyria: (Pach-, Greek, thick) Broadening of the gyrus. Agyria and Pachygyria denote macroscopical abnormalities of the cortical surface associated microscopically with a thickened cortical ribbon. The cortical ribbon is usually greatly thickened and the underlying white matter is markedly reduced. Pachygyria represents a milder degree of cortical malformation with peresistence of secondary and some tertiary sulci. Microscopically, a four-layered cortex is a common finding. See also lissencephaly.

#Pallium: the cerebral cortex viewed in its entirety, i.e., the mantle of gray matter covering both cerebral hemispheres. Also, this term is also used to describe the cerebral cortex during its development.

#Phenyltoin: use of phenytoin during pregnancy carries a risk of microcephaly and minor congenital anomalies including nail hypoplasia and facial dysmorphism. More severe malformations such as anterior encephaloceles have also been reported.

#Pia-ependymal seam: this term refers to the fused product between the pia and the ependymal tissue in schizencephaly. Shaw and Alvord questioned the conceptual and observational truthness of this concept.

#Placode: local thickening in the embryonic ectoderm layer; the cells of the placode ordinarily constitute a primodial group fron which a sense organ or neruons of sensory ganglia will be derived. Other elements of these ganglia arise from the neural crest.

#Poikilothermia: Marked daily fluctuations in body temperature.

#Polygyria: Excessive superficial sulcation with normal microscopical architecture associated with hydrocephalus.

#Polymicrogyria:

· First described by Bielschowsky. Polymicrogyria describes gyri that are too numerous and too small. Sometimes the appearance is one of wide gyri with a central dimple, the so-called Morocco leather appearance, which can be mistaken for pachygyria. The abnormal cortical ribbon can be abnormally thick or thin, hypercellular or hypocellular.

· Polymicrogyria can be focal or widespread. Sometimes they follow a particular arterial territory and are bilateral and symmetrical (usually the middle cerebral artery). Some of them are confined to the opercular region or depths of the insula. Polymicrogyria can occur at any part of the cerebral hemisphere but often at the edge of destructive lesions.

· A single organized layer or four-layered cortices are often but not always seen. Many other patterns have been described. Characteristically, fusion of the molecular laryer between two abnormal gyri is seen, a feature that separate polymicrogyria from microgyria.

· The etiology of polymicrogyria includes intrauterine ischemia and insults such as infections, rare inherited familial syndromes such as Aicardi syndrome, metabolic diseases such as Pelizaeus-Merzbacher disease and Leigh’s disease, and peroxisomal disorders such as Zellweger’s syndrome.

#Porencephaly: (poro: latin, means a small opening) A smooth-walled cyst with communications that extends from the ventricle to the brain surface. The lesions may be symmetrical. A porus is best defined as a circumscribed hemispheric defect originating during fetal life and antedating the acquisition of mature astroglial responses or completion of convolutional development. Most commonly seen as around the Sylvian fissure, often symmetrical and bilateral.

· Note that the communication is always only with the ventricle since the preservation of the molecular layer of the cortex results in a pia-glial membrane that prevents communication with the subarachnoid space [according to Shaw and Alvord].

#Proencephalic dysgenesis: includes arhinencephaly, holoprosencephaly, agenesis of the corpus callosum, fused thalami, hypoplastic third ventricle, small optic nerves, microphthalmia, small or absent pituitary gland, microcephaly, cleft of high arched palate, and micrognathia.

#Probst bundle: Also called longitudinal corpora callosa. They are abnormal prominent bundle of fibers in median sagittal directions (longitudinal callosal fibers) in the lateral part of the roof of the lateral ventricles in cases of agenesis of corpus callosum. The volume of Probst bundle is significantly smaller than that of the corpus callosum.

#Pseudo-aprosencephaly (vesicular forebrain): In these cases, the forebrain exists as a thin walled vesicle composed of gliotic tissue with an ependymal lining. An intact, albeit microcephalic, cranial vault to be present (otherwise it will be anencephaly or exencephaly). [C. Sergi, H. P. Schmitt, Acta Neuropathologica 2000 99:277]

#Ptergyium: A winglike structure, especially an abnormal triangular fold of membrane in the interpalpebral fissure, extending from the conjunctiva to the cornea. A pterygium can also form in a joint.

Syndromes and Sequences: Head

#Pallister-Hall syndrome: Pallister-Hall syndrome is a disorder of development and inherited in an autosomal dominant trait with variable expressivity. It has been linked to mutations of the GLI3 gene on chromosome 7p13 which encodes a zinc finger transcription factor. The primary feature of Pallister-Hall syndrome is hypothalamic hamartoma, additiona features consistute a spectrum of anomalies including, hypopituitarism, polydactyly and other limb anomalies, laryngeal anomalies, imperorated anus and other visceral malformations. Case with mild presentation including asymptomatic ones have been described. [Hall JG et al., Am J Med Genet 1980; Kuo JS et al., 1999]

#PEHO syndrome: Progressive encephalopathy wiuth Edema, Hypsarrhythmia, and Optic nerve atrophy. Probably autosomal recessive. Onset of symptoms is from 2 to 16 weeks and they consist of infantile spasms, severe hypotonia, profound psychomotor retardation, transient subcutaneous edema and blindness. In one of the cases being studied, there is virtual loss of the internal granule layer with preservation of Purkinje cells (although morphologically abnormal), and demyelination in optic nerve.

#Pena-Shokeir Syndrome: An autosomal recessive lethal condition that comprises camptodactyly (campto- means bending, flex), multiple ankyloses, arthrogryposis, facial dysmorphism, polyhydrammnios, fetal growth retardation, and pulmonary hypoplasia. Neuropathologic changes include multicystic encephalopathy, polymicrogyria and intense reactive gliosis, and heterotopias. [Pena SD and Shokeir MH, 1974; Hall JG, 1986]

#PHACES Syndrome: Posterior fossa malformations, Hemangiomas of the cervicofacial region, Arterial anomalies, Cardiac anomalies, Eye abnormalies, and Sternal or abdominal clefting or ectopia cordis. Marked predominance among female infants and is thought to represent a developmental-field defect that occurs between 8 and 10 weeks of gestation. These infants are at risk of cerebral occlusive disease.

#Proteus syndrome: (Proteus: Greek Mythology, A sea god who could change his shape at will.) This is an ectomesodermal syndrome and is commonly misdiagnosed as neurofibromatosis Proteus syndrome has very variable expression and most proven cases are sporadic. Patients have overgrowth of variuous body parts, hemihypertrophy, asymetric body growth or macrodactyly, verrucous epidermal nevi, thickening of skin, cerebriform masses on soles of hands and feet, lipomas, subcutaneous keratoses, various skeletal abnormalities. Panter skin hyperplasia (the so-called “”moccasin lesion”) is frequet and useful diagnostic feature. Various ocular abnormalities including colobamas, glaucoma, and ertinal detachment can occur.

· CNS abnormalities: Hemimegalencephaly is frequent. There is mental retardation in 1/3 of cases, other neurologic manifestations include seizures, abnormal EEG, hydrocephalus, and high incidence of meningioma.

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