Iniencephaly is a rare and complex neural tube defect involving a defect to the occipital bone, spina bifida, and severe distortion of the cervical and thoracic spine with retroflexion of the head.
Abstract: Iniencephaly is a rare and complex neural tube defect involving a defect to the occipital bone, spina bifida, and severe distortion of the cervical and thoracic spine with retroflexion of the head. While environmental and genetic causes have been implicated, its etiology and pathogenesis are poorly understood. Prenatal diagnosis can be suspected during the first-trimester scan and confirmed from the early second trimester onwards. The prognosis for infants with iniencephaly is extremely poor.
Keywords: iniencephaly; neural tube defect
Authors: Maria J. Rodríguez-Sibaja, Sandra Acevedo-Gallegos, Juan M. Gallardo-Gaona 1
- National Perinatology Institute, Maternal-Fetal Medicine Division, Mexico City, Mexico
Reviewers: Mario I. Lumbreras-Marquez, Karen Fung-Kee-Fung
Iniencephaly is a rare and complex neural tube defect involving a defect to the occipital bone, spina bifida, and severe distortion of the cervical and thoracic spine with retroflexion of the head. Moreover, iniencephaly is sometimes combined with occipital encephalocele or rachischisis of the cervical or thoracic spine.(1)
The incidence of iniencephaly at birth ranges between 0.01-1:1,000(2); however, the actual frequency is unknown because a significant number of cases are not recognized as such.(3) There is a female predominance, with a reported male to female ratio of 7:17.(2)
The etiology of iniencephaly is poorly understood; both environmental and genetic causes have been investigated.(4) It has been described as a consequence of congenital syphilis(3), maternal diabetes(5), and in animal models, associated with the use of teratogenic chemicals such as triparanol, streptopnigrin, and vincaleucoblastine.(3) Some chromosomal abnormalities, including trisomy 18, 13, and monosomy X, have also been associated with this disorder.(1,4) Most cases are sporadic and probably related to polygenic inheritance.(3)
Iniencephaly is thought to be the result of an early closure defect on the base of the skull in association with dysraphism of the cervical spine, resulting in a fixed retroflexion of the head and severe lordosis of the cervicothoracic spine.(3)
Iniencephaly is associated with other anomalies in 75% of the cases.(1,6) The most frequent accompanying malformations affect the central nervous system (e.g., anencephaly, encephalocele, meningomyelocele, Dandy-Walker malformation, hydrocephalus, holoprosencephaly, lissencephaly). Nonetheless, malformations involving other organs and systems may also be observed (e.g., omphalocele, congenital diaphragmatic hernia, lung and heart defects, gastrointestinal atresia, renal agenesis, or dysgenesis, regression sequence, facial clefts, club foot, single umbilical artery).(1–3)
Prenatal diagnosis of iniencephaly can be confirmed by ultrasound from the early second trimester onwards, although there are reports of earlier first-trimester diagnosis.(1,3) The sonographic diagnosis relies on three fundamental features (i) occipital bone defect that results in an enlarged foramen magnum; (ii) partial or total absence of the cervical and thoracic vertebrae with abnormal fusion and incomplete closure of those vertebrae present; and (iii) fixed hyperextension of the malformed cervicothoracic region resulting in a significant shortening of the spine and upward-turned face.(2,3,6,7) Moreover, iniencephaly is sometimes combined with occipital encephalocele or rachischisis of the cervical or thoracic spine. Polyhydramnios is frequently associated with iniencephaly due to compromised fetal swallowing.(1,2) Two types of iniencephaly are recognized based on the presence or absence of encephalocele, iniencephalus apertus, and iniencephalus clausus, respectively.(1,2)
Iniencephaly differential diagnosis includes craniorachischisis with spinal retroflexion. Moreover, anencephaly with spinal retroflexion is one of the primary differential diagnoses of iniencephaly apertus(4); however, anencephaly is associated with an absence of skin cover of the head, likewise, in most cases, the cervical spine is intact.(3,4) The differentiation between iniencephaly clausus and Klippel-Feil syndrome (KFS) a congenital defect in the formation or segmentation of the cervical spine with a wide spectrum of associated anomalies is complex and controversial as some authors regard KFS as the mildest form of iniencephaly(2); a fusion of the cervical vertebrae may be present in both; however, retroflexion of the head is usually not seen in KFS.(4) Other entities presenting with a fixed retroflexion of the head such as anterior cervical tumors (e.g., teratoma, goiter, and lymphangioma), cervical myelomeningocele, encephalocele, congenital neuromuscular disorders, and Jarcho-Levin syndrome should also be considered in the differential diagnosis (1,3,4).
The prognosis for infants with iniencephaly is extremely poor.(2,3) So far, the literature has only documented a few survivors with iniencephaly; however, these are rare examples of survival, and this information should be interpreted with caution when counseling pregnant individuals whose pregnancy is complicated by this condition.(3,5,6)
The recurrence rate of iniencephaly is less than 1%, although it may be higher in families with a history of other neural tube defects.(3,6) Importantly, folic acid supplementation (e.g., 4 mg/day) reduces the risk of iniencephaly and other neural tube defects.
Because of the poor prognosis of iniencephaly, termination of pregnancy is common in countries where it is legal. Where elective abortion is prohibited, the main obstetrical goal is to avoid labor dystocia and maternal trauma due to the corporal distortion of the fetus during delivery. Induction of labor, while there is still an adequate cephalopelvic proportion, reduces the maternal risks and probably avoids an unnecessary cesarean delivery.(3)
1. Chen C-P. Prenatal diagnosis of iniencephaly. Taiwan J Obstet Gynecol. 2007 Sep;46(3):199–208.
2. Joó JG, Beke A, Papp C, Szigeti Z, Csaba A, Papp Z. Major diagnostic and pathological features of iniencephaly based on twenty-four cases. Fetal Diagn Ther. 2008;24(1):1–6.
3. Sahid S, Sepulveda W, Dezerega V, Gutierrez J, Rodriguez L, Corral E. Iniencephaly: prenatal diagnosis and management. Prenat Diagn. 2000 Mar;20(3):202–5.
4. Kulkarni PR, Rao R V, Alur MB, Joshi SK. Iniencephaly clausus: A case report with review of literature. Vol. 6, Journal of pediatric neurosciences. 2011. p. 121–3.
5. Aytar MH, Doğulu F, Cemil B, Ergün E, Kurt G, Baykaner K. Iniencephaly and long-term survival: a rare case report. Child’s Nerv Syst ChNS Off J Int Soc Pediatr Neurosurg. 2007 Jun;23(6):719–21.
6. Pungavkar SA, Sainani NI, Karnik AS, Mohanty PH, Lawande MA, Patkar DP, et al. Antenatal diagnosis of iniencephaly: sonographic and MR correlation: a case report. Korean J Radiol. 2007;8(4):351–5.
7. Gadodia A, Gupta P, Sharma R, Kumar S, Gupta G. Antenatal Sonography and MRI of Iniencephaly apertus and clausus. Fetal Diagn Ther. 2010;27(3):178–80.
This article should be cited as: Maria J. Rodríguez-Sibaja, Sandra Acevedo-Gallegos, Juan M. Gallardo-Gaona: Iniencephaly, Visual Encyclopedia of Ultrasound in Obstetrics and Gynaecology, www.isuog.org, July 2022.
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