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2000-02-18-05 Answer of case of the week #19 © Diaz Guerrero www.TheFetus.net

Answer to case #19

February 18-March 3, 2000

Submitted and discussed by Luis Guillermo Diaz Guerrero, MD, and Alberto Sosa Olavarría MD. PhD, Perinatology Unit - Carabobo University, Valencia , Venezuela

This is a different type of case this time... instead of a great big baby... these are several images from a 12 week old fetus.

Overall view of the baby. What is striking is the shape of this fetus. The most striking finding was the impossibility of seeing the neck of the baby. There is hyperextension of the fetal head with the axis of the face in a perpendicular line with the axis of the fetal body. The head is not well delineated because there is a large occipital cephalocele.

"down-pointing" Genital tubercle:  = female gender

The femur

The back of the head

Findings

  • The abnormal shape of the fetus with no distinct separation between the head and the body.
  • The position of the face in relation of the body.

Many had though about an acardiac twin and indeed such a fetus could have the same appearance… but there should be a co-twin, and I would have mentioned it !

Others had suggested a limb-reduction syndrome like Robert’s syndrome. The limbs where not very visible, but findings that are not abnormal are not usually shown, and those condition should not have anomalies of the neck. That femur was normal length.

In order for the head to be in such an unusual position, the spine has to be very abnormal, and this was the very difficult part of this case: at 12 weeks the spine is barely visible. If this had been an older fetus, findings a crooked spine with a retroflexed head would have suggested Iniencephaly, which is what this case represented.

The pregnancy was interrupted. The pathology specimen shows a perfect correlation with the echographic findings. Notice the spine in the second image. This is very typical of ininencephaly.

INIENCEPHALY

Definition

 Abnormality of the fetal cervical vertebrae associated with an excessive lordosis of the cervicothoracic spine and neural tube close defects.

Classification 

 -Open: associated with open bifid spine, rachischisis

-Closed: closed defect

Incidence

Sporadic, rare condition. M1:F10. Prevalence in Northern China is 25 times more frequent than in the USA. In our clinic:  1: 3783 echographic studies in high-risk pregnancies

Etiology

There are some hypotheses that try to explain the etiology of iniencephaly, first, it has been associated with dilatation and rupture of the neural tube once it had closed1, lack of closing of the neural tube during embryogenesis2, early vascular disruption process3 with alteration of the normal angiogenesis of the vessels being in charge of the neural tube perfusion with the consequence malformation.

Jones et al. showed some clinical evidence that support the hypothesis that the axial dysraphism defects can result from primary alterations of the embryonic mesoderm, this would explain the associated mesodermal defects that can be seen in iniencephaly4. There have been reported associations of iniencephaly with some substances: hypnotics, vinblastine, estreptonigrina, triparanol, diseases as maternal syphilis and consanguinity of parents5,6,7.

Embryology

Abnormal development of the rostral portion of the notochord and sommits of the cervico-occipital region that produce an imperfect development of the cranium skull base, hyperextension of the head, short spine with rachischisis and persistence of the embryonic cervical lordosis. (3rd week)

Transmission

Sporadic. Kjaer et al. proposed that iniencephaly could be the result of the deviation of the genetic expression in the embryonic period, affecting the dorsoventral body axis orientation anatomically seen in the malposition of the notochords8.

Diagnosis

Sonography

  • Marked hyperextension of the fetal head, very short, lordotic, cervical spine.
  • Perpendicular face in relation with body axis
  • Occiput absence without nuchal depression
  • Open cervical spine with meningocele
  • Anencephaly frequently present.
  • Lumbosacral myelomeningocele, caudal regression
  • Earliest diagnosis reported: 13 weeks (9,10)

Laboratory

  • Elevated alpha-fetoprotein

Pathology

  • Squamous occipital defect, body and arc of the cervical vertebrae
  • Brain prolapse trough distended occipital foramen
  • Severe lordosis of the cervical spine
  • Micrencephaly
  • Polymicrogyria
  • Ectopic glial tissue in leptomeninges
  • Cerebral ventricular system atresia
  • Vermian agenesis, cerebellar cysts
  • Spinal cord tissue disorganization.
  • Vascular disruption of the cervical and vertebral vases, common carotid trunk. (See figure 2 and 3)

Genetic Anomalies

Not associated with syndromes, isolated cases of XO monosomy

Differential Diagnosis

  • Anencephaly with cervical retroversion
  • KlippelFeil syndrome
  • Cervical encephalocele
  • Cervical teratoma

Associated Anomalies

CNS:

  • Rachischisis
  • Diastematomyelia
  • Anencephaly
  • Encephalocele
  • Hydrocephalus

OTHER SYSTEMS:

  • Absent mandible, cleft palate
  • Cardiac anomalies, heart dextroposition, common carotid artery, transposition of great arteries
  • Diaphragmatic hernia
  • Umbilical artery agenesis
  • Omphalocele, hepatoomphalocele
  • Gastroschisis
  • Situs inversus
  • Polycystic kidneys, horseshoe kidney
  • Arthrogryposis
  • Clubfoot.
  • Polyhydramnios.

Prognosis 

  • Almost always lethal11.

Management

Pregnancy termination

Folic acid supplementation in following pregnancies

 See also Iniencephaly

References

 1- Gardner WJ. Klippel Feil syndrome, iniencephalus, anencephalus, hindbrain, hernia and mirror movement. (1990) Overdistention of the neural tube. Child’s Brain; 5: 361-379.

 2- Scherrer C., Hammer F., Schinzel A., Briner J. Brain stem cervical cord dysrrhaphic lesion in iniencephaly. Pediatr Pathol. 12(3): 469-76

 3-Stevenson RE., Kely JC., et al. ( 1987)  Vascular basis for neural tube defects: a hypothesis.  Pediat 80(1): 102-106

 4- Jones MC, Jones KL, Chernoff GF (1982) Posible mesodermal origin for axial dysraphic disorders. J Pediatr  Nov;101(5):845-9

 5-Garofalo R., Simosa V., Morean F. ( 1990) Defectos del cierre del tubo neural. Arch Venez Pueric Pediat 53(2): 85-89.

 6-Sosa Olavarría A.: Ultrasonografía y Clínica Embriofetal. Valencia, Venezuela. Editorial Tatum, 1994.

 7-Bermúdez A.,Sosa Olavaria A., Rivas M.,Mira M. ( 1995). Iniencefalia: serie de seis casos. Rev Obstet Ginecol Venez, 55(3): 161-165

 8- Kjaer I, Mygind H, Fischer Hansen B. (1999) Notochordal remnants in human iniencephaly suggest disturbed dorsoventral axis signaling. Am J Med Genet  Jun 11;84(5):425-32

 9-Sherer DM. (1993) Endovaginal sonographic diagnosis of iniencephaly apertus and craniorachischisis at 13 weeks, menstrual age. J. Clin. Ultrasound. Feb 21(2):127-7.

 10- Sanders R. (1996) Iniencephaly. In : Structural fetal abnormalities. St. Louis, Mosby-Year Book, 39-40

 11-Katz VL., Aylsworth AS., Albright SG. ( 1989): Iniencephaly is not  uniformly fatal. Prenatal Diagn. ; 9:595-599.

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