The term iniencephaly implies deficiency of occiput in the region of foramen magnum, spina bifida of considerable extent and retroflexion (extreme extension) of the spine. In most cases the cranial cavity is well formed and skin over the retroflexed region is uninterrupted. Howkins and Lawrie(1) in 1939 classified iniencephaly into simple iniencephaly (clausus-no encephalocele and apertus-with encephalocele) and anencephaly with spinal retroflexion. However, the etiopathological distinction between these two entities was not established(2) until recently where anencephaly is considered by some(3,4) as associated CNS malformation with iniencephaly. The incidence of iniencephaly has been estimated to be between 1 in 900(5) to 1 in 2200(6) deliveries; whereas from India it has been reported to be 1 in 60,000 deliveries(7). We have come across 19 cases of iniencephaly in over 6^1/2 years period among 102 malformed fetuses referred to our center for fetal autopsy. The referral diagnosis in 13 of them was anencephaly or multiple congenital anomalies, i.e., incorrect. This paper presents detailed demographic, clinical, radiologic and necropsy findings of the 19 iniencephaly cases. Our data supports that simple iniencephaly and anencephaly with spinal retroflexion (here, we like to designate as iniencephaly with anencephaly) are same entity and not a rare malformation around Lucknow.

Subjects and Methods

Nineteen iniencephaly/iniencephaly with anencephaly were referred to the Genetic Center over 6^1/2 years period from March, 1991 to October, 1997. Four cases were diagnosed antenatallyas iniencephaly (3 cases) or iniencephaly with anencephaly (1 case) before termination of pregnancy by antenatal ultrasonography; 2 cases were referred correctly as iniencephaly after delivery by clinical examination whereas 13 cases were labelled as multiple congenital anomalies or anencephaly even after delivery (i.e., unable to recognize the condition).

A detailed external examination, chromosomal analysis (one from each group), anthropologic measurements, necrography, computerised tomography (two from each group) and protocol based necropsy were performed as per standard procedure. Body weight, organ weight and other measurements were compared with the standards described by Wigglesworth and Singer(8). Gestational age was calculated from last menstrual period and ultrasonographic femur length, and after delivery with foot length. Fetal sex was noted. Cases were divided into two groups: Group A - Simple Iniencephaly, 8 cases (clausus - 7 cases (Fig. 1a); apertus - 1 case) and Group B - Iniencephaly with anencephaly, 11 cases (Fig. 2a).



 

Fig. 1(a) Clinical photograph (lateral)

Information was collected on birth order, month of conception, ethnic back- ground, consanguinity, parental age at conception, periconceptional events, maternal drug exposure, maternal illness, family history of birth defects and maternal past obstetric history. The results are compared between the two groups.



 

Fig. 1(b) CT (saggital) of simple iniencephaly (clausus) showing exaggerated retroflexion and cervicothoracic vertebral anomalies.

Fig. 2. (a) Clinical photograph (lateral),	Fig. 2(b). CT (saggital) of iniencephaly with anencephaly showing anencephaly in addition to cervicothoracic vertebral anomalies and retroflexion as in Group A.

 
Results

Among 19 cases of iniencephaly/iniencephaly with anencephaly, 8 were simple iniencephaly (7 clausus and 1 apertus) and eleven were iniencephaly with anencephaly. All 19 cases fulfilled 3 major diagnostic criteria, namely, occipital bone defect, spinal rachischisis and cervicothoracic spinal retroflexion. Detailed observations on demographic characteristics of the two groups are given in Table I. There was excess of females in both the groups. There was no parental consanguinity. The mean parental age at conception was quite similar in the 2 groups (Table I). The number of 1st trimester spontaenous abortions (missed abortions) was also com- parable between the two groups. There was one precurrence of NTD (anencephaly; female) in Group A whereas the figure for Group B was 4 (anencephaly-one, anencephaly with limb defect-one and lower spina bifida, not specified-two; 3 were fernale). Most of the cases were from Hindu middle class vegetarian families around Lucknow (Table I). There was no seasonal effect on conception between the groups (winter was the commonest). There was no history of exposure to drugs or radiation or infection in early pregnancy in either group. Nine pregnancies were associated with polyhydramnios (3/8 in Group A and 6/11 in Group B) and one complicated with pregnancy induced hypertension (Group B). All cases demonstrated disturbance of growth as characterized by reduced weight and organ hypoplasia. The detailed observations on associated anomalies are given in Table II. The differences were insignificant. Craniospinal CT was carried out in 4 cases (2 from each group). It provided more clear bony demarcation of occipitocervical region in comparison to necrogram. CT findings in Group A (Fig. 1b) were widely separated sutures of vault bones, large foramen magnum, defective formation of base of skull and sella turcica, well formed facial bones, severe abnormality of spine (cervical vertebrae - reduced in number, hypoplastic, deformed, fused and without arch; thoracic vertebrae - multiple congenital anomalies), widened neural canal, absence of spinal cord in upper portion and hypoplasia of cerebellum and vermis in 3 (including Dandy Walker malformation in 2; most cases were noninformative due to degenerative changes in brain or anencephaly). The CT findings in Group B (Fig. 2b) were similar except there were no vault bones, no brain tissue and marked hypoplasia of facial bones.

Chromosomal analysis did not reveal any abnormality in 2 cases (one from each group).

 

Discussion

Iniencephaly is a developmental error occurring in early pregnancy prior to closure of cephalic neural folds at 24 days gestational age(8). It is characterized by arrest as well as imperfect development of base of skull (portion of neural tube) and vertebral column (cervicothoracic region mainly). At the early stage of embryo, paravertebral sclerotome (mesoderm) differentiates into two parts, a ventral mass (forms the vertebral bodies, pedicles and their cranial homologous) and a dorsal mass (forms neural arches and vault bones of the cranium). In iniencephaly, one or both of these masses are hypoplastic or ill developed.