Glossary in Congenital Malformations

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General:

#Dentato-olivary dysplasia: Usually part of a more extensive complex of malformation. Inferior olivary nuclei lack induration and the dentate nuclei are in form of large club-shaped masses of gray matter.

#Decussation of pyramidal tracts: Decussation of pyramidal tracts are often asymmetrical. The ventral cortical spinal tracts can be variable in size and may be completely absent (The anterior corticospinal tracts extends normally only as far as the cervical or thoracic region). Variation in the decussation is usually asymptomatic.

#Deformation: represent an alteration in form or structure resulting from mechanical factors.

#Developmental: developmental malformations and structural abnormalities refer to growth disorders that occur during the developmental period after birth. However, the etiology may be present before birth.

#Diabetes mellitus: infants of diabetic mothers have an overall incidence of major malformations is 6% to 9%. The incidence of holoprosencephaly in infants born to a diabetic mother is about 1%, a 200 times increase in risk relative to the general population. No definite phenotype for diabetic embryopathy exists. Defects of heart, CNS (esp. neural tube defects), kidneys, and skeleton predominate. Caudal regression, a rare malformation, are several hundred folds more common in infants born to a diabetic mother.

#Diastematomyelia: (-diastema, Greek, a space, interval) Abnormal congenital divison of the spinal cord by a bony spicule or fibrous band protruding from a vertebra or two, each of the half surrounded by a dural sac (i.e., co-existence of two hemicords). The fibrous septum will separate the cord into two hemicords (i.e., each with only one anterior horn and posterior horn).

#Dimyelia: Complete duplication of the spinal cord as seem in types of conjoined twins, wuch as dicephalus dibrachus.

#Diplomyelia: Lengthwise fissure and seeming dobuleless of the spinal cord (i.e., duplication of the cord). Morphologically, two complete cords (e.g., with two anterior horns) going along each other are noted. Both spinal cords are contained within the same dural sac.

#Disorder of ventral induction: This term designates those malformations that seem to result from induction failure involving the three germ layers: cephalic mesoderm; adjacent neuroectoderm and associated neural crest derivatives and entodermal anlagen for facial structures. Induction failure is probably time-specific as ventral indcution is completed prior to the 33rd day of intrauterine life. The major defect is failure of the primary cerebral vesicle (telencephalon) to cleve and expand laterally. Midline facial defects are often present (the face predicts the brain). Genetic mechanisms include autosomal dominant and, less often, recessive transmissions, and chromosomal defects such as trisomy 13 and, less common, trisomy 18.

#Disruption: disruption is defined as a structural anomaly of an organ, part of an organ, or a larger region of the body resulting from the extrinsic breakdown of, or an interference with, an originally normal conceptus.

#Dysplasia: an abnormal organization of cells into tissue(s) and its morphologic result(s). In other words: a dysplasia is the process (and the consequence) of dyshistogenesis.

#Dysraphia: Incomplete closure of the embryonic neural tube (i.e., neural tube defect). Neural tube defects are very common severe congenital malformations. They are observed in 8.8% of spontaneous abortions and 0.08% of fetuses on 10-14 weeks prenatal ultrasound examination.

Syndromes and Sequences:  Head

#Dandy-Walker Syndrome: The three essential features are: complete or partial agenesis of the vermis, cystic dilatation of the fourth ventricle and enlargement of the posterior fossa. Hydrocephalus is a frequent but inconstant finding. Other CNS findings include elevation of the tentorium cerebelli and lateral, transverse sinuses and torcula (torcular Herophilli), and lack of patency of the foramina of Magendie and Luschka. Other cerebral and visceral anomalies are present. It is the presene or absence of other cerebral and viseral abnormalies that determines the prognosis of individuals. About 68% of all cases have other developmental abnormalities of the CNS. Facial abnormalities may also be seen.  

#Deletion 22 syndromes (#Catch 22 syndrome): Three sydromes that are originally thought to be three separate syndromes are included but their clinical phenotype overlap. The overall incidence of all three disorders is about 1 per 3,000 to 4,000 in the general population. Catch 22 (cardiac abnormalities, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia, and deletion on chromosome 22) is acronym. The 22q deletion syndromes include:

·         DiGeorge syndrome (DGS): Thymic aplasia, T-cell mediated immune defects, hypoparathyroidism, cardiac defects, and characteristic facial anomalies).

·         Conotruncal anomaly face syndrome (CTAFS): Characteristic facial features, conotruncal anomalies, and developmental delays.

·         Shprintzen syndrome or velocardiofacial syndrome (VCFS): Characteristic facial features, learning problems, cardiac anomalies, cleft paltes, or velopharyngeal incompetence.

#De Morsier Syndrome (Septo-optic dysplasia):

·         Summary: Optic hypoplasia, septo-aplasia, and hypopituitarism.

·         Genetics: Not genetically determined. Environmental factors, in particular maternal diabetes mellitus, play a role.

·         Clinical: Variable degree of visual disturbance. Double contour optic disc is of great diagnostic value (the optic discs have a characteristic appearance with a central part of less than half the normal diameter of the papilla, which represent the true disc, and a peripheral ring of about the size of a normal papilla). Hypopituitarism is an important finding; more common abnormalities are growth hormone deficiency and diabetes insipidus.

·         Pathology: Optic nerve hypoplasia, aplasia or defects of the septum pellucidum (inconstant finding), and pituitary-hypothalamic dysfunction (hypopituitarism). The floor of third ventricle, a structure embryonically related to the development of the optic placodes, is abnormal in some cases. Olfactory aplasia is frequent. Other features include elevation of the tentorium cerebelli and lateral and transverse sinuses and torcula, lack of patency of the foramina of Magendie and Luschka, and hydrocephalus. Not all these features are present in every case.  

#Down syndrome: See Trisomy 21.

#Duane’s retraction syndrome: See also anormalous axonal connection (guidance) syndromes.

·    Clinical: Duane's syndrome is an unusual congenital form of strabismus where there is paradoxical anomalous lateral rectus innervation of the affected eye due to misdirection of axons destined for the medial rectus. Three types of Duane's syndrome are recognized: type I is the most common (70-90% of all cases) and has defective abduction but normal or minimally defective adduction; type II has normal adduction but defective abduction and exoptia of the affected eye; type III has defective adduction and abduction. Duane's syndrome is heterogeneous at multiple levels with variations in its ocular manifestations, accompanying systemic manifestations and in the chromosomal loci with which it may be associated. [Gutowski NJ, Eur J Neurol 2000 Mar;7(2):145-9]

·         Association: Several autosomal dominant syndromes with dysmorphic features are associated with Duane's syndrome. Duane’s syndrome has also been associated with other anormalous axonal connection (guidance) syndromes. Wildervanck syndrome is the most common multiple congenital abnormality associated with Duane’s syndrome.

·         Genetics: Over 90% of Duane's syndrome are sporadic but up to 10% are familial, usually with autosomal dominant inheritance. Chromosomal loci for genes contributing to Duane's syndrome have been suggested at 4q27-31, 8q12.2-q21.2 and 22pter-22q11.2.

NeuroLearn NeuroHelp Malformations General Syndromes For Comment: KarMing-Fung@ouhsc.edu