Acalvaria: A rare congenital malformation.

Acalvaria is described as a rare congenital malformation in a 1-month-old female baby who presented with classical clinical features of soft, lax skull as a result of absent skull bones and associated muscles. Acalvaria is usually a fatal anomaly and is rarely discussed in English literature. Thus, we herein report a living case of acalvaria along with a review of the literature.

Introduction

Acalvaria is an extremely rare congenital malformation characterized by an absence of flat bones of skull, dura mater, and associated muscles in the presence of normal cranial contents and facial bones.[1-3] Although its pathogenesis is unclear it has been explained by the theory of post-neurulation defect.[12] It has been considered a fatal congenital anomaly and only a handful of cases have been reported in English literature till date.[1-3] Thus, we herein present the present case which to the best of our knowledge is third living case of acalvaria.[1-3] The pertinent literature is reviewed with the aim to make physicians aware regarding the clinical features of this uncommon fatal clinical anomaly so that undue associated morbidity could be avoided by prompt antenatal diagnosis and subsequent management.

Case Report

A 1-month-old female infant presented with soft, lax skull without any scalp abnormality. The baby was born at term by cesarean section and was second issue of consanguineous marriage, the first one being a male. The available antenatal record suggested a normal ultrasound examination and the other complications of pregnancy including any history of drug intake, radiation exposure, etc., were absent. The post-natal history suggested normal milestones and development for age without any other clinical symptoms.

On examination, the baby appeared active weighing 3,910 g with head circumference of 35 cm. The skull and face appeared normal on inspection with healthy skin cover. On palpation, the frontal, temporal, and occipital bones were absent in upper part, whereas parietal bones could not be palpated. The facial bones and rest of the physical examination were normal without any associated anomaly. Neurological assessment for age suggested no abnormality. The roentgenogram of skull suggested complete absence of parietal bones, and the frontal, occipital, and temporal bones were not visualized in upper aspect [Figure 1]. The computed tomography scan of brain confirmed the bony defect with presence of normal cranial contents and ventricular system [Figure 2].

Figure 1

Plain roentgenogram skull showing absence of skull bones

Figure 2

Computed tomography scan head (slice image) showing absence of skull bones with normal cranial contents

The baby was managed conservatively with a vigilant examination on close follow-up along with parental counseling and reassurance. The patient is presently having normal development without any apparent neurological abnormality on regular follow-up for the last 2 months.

Discussion

Acalvaria is an extremely rare congenital malformation in pediatric age group.[1-3] It is characterized by the absence of bones of cranial vault, dura mater, and associated muscles.[1-3] Although central nervous system and cranial contents are usually unaffected, but still neuropathological defect of some extent has been reported in few cases.[12] Similarly, acalvaria has been reported in association with other anomalies such as holoprosencephaly, micropolygyria, facial clefts, cardiac anomalies, club foot, etc., thereby emphasizing need for a thorough clinical evaluation so as to assess the prognosis and the final outcome in such rare cases.[1-4]

The etiopathogenesis of acalvaria is still unknown.[12] It is considered a heterogenous disorder without any genetic predilection and correlation to folic acid intake.[1] A review of literature suggests that different investigators have explained the embryological basis of this rare malformation by theory of post-neurulation defect.[125] Normally, around 4th week of gestation and after closure of anterior neural pore, there is migration of mesenchymal tissue under ectoderm which forms skin and scalp, but the mesenchymal tissue develops into skull bones and associated muscles.[125] Thus, faulty migration of mesenchymal tissue in presence of normal development of ectoderm results in an absence of flat bones of skull and associated muscles.[125] Although not widely accepted, but still some investigators consider acalvaria to be a part of spectrum of anencephaly, whereas others explain its pathogenesis on the basis of failure of primary closure of neural tube.[126]

The clinical presentation as experienced in present and reported cases is heralded by the presence of soft, lax skin covered skull due to absence of flat bones of cranial vault and associated muscles.[1-3] The facial bones and cranial contents are usually normal, although some neuropathological abnormality has also been reported.[1-3] Since acalvaria remains a fatal congenital malformation, an insight into its radiological features demands special emphasis because a timely antenatal diagnosis followed by an appropriate intervention could prevent the undue morbidity, mortality, and psychological trauma resulting at term. Although different craniofacial anomalies including anencephaly, hydrocephalous, osteogenesis imperfecta, hypophosphatasia, etc., remain important radiological differential diagnosis, but still as experienced by different investigators, a vigilant transvaginal ultrasound scan examination around 12 weeks of gestation can accurately diagnose acalvaria in most of the cases.[1267] The presence of normal cerebral hemispheres remains main sonographic feature differentiating acalvaria from anencephaly which remains most common antenatal differential diagnosis.[6-8] Among laboratory investigations, alpha-fetoprotein level is usually raised, whereas unconjugated estradiol levels are usually undetectable.[12]

The initial treatment of acalvaria is mainly conservative aimed at supportive care and management of any associated anomalies if present.[2] Being a rare anomaly with only two reported living cases, the surgical treatment for correcting the skull defect has not been discussed in literature till date. The presence of spontaneous bone growth as observed in few cases of scalp defect, such as cutis aplasia, highlights the importance of initial conservative management and supportive care in patients with acalvaria. They can subsequently undergo skull reconstruction by bone grafting and cranioplasty at school going age.[9]

Since the only living case of this fatal anomaly with long-term follow-up is severely mentally retarded and disabled requiring specialized medical and social care, so we conclude that antenatal diagnosis of this fatal anomaly by a vigilant radiological evaluation is extremely important so that the morbidity, mortality, and the associated psychological trauma resulting at the time of birth and on subsequent management could be prevented.