Fetal osteogenesis imperfecta

Clinical History

We report the case of a planned pregnancy in a healthy 36-year-old woman. There was a prior uncomplicated pregnancy that gave rise to a healthy child. There was no consanguinity, no family history of previous disease. There were no known exposures to any teratogens. Folic acid supplementation was initiated pre-conception.

Imaging Findings

At 16 weeks of gestation, a routine antenatal ultrasound identified multiple skeletal abnormalities. The biparietal diameter (BPD) measurements were consistent with gestational age, the skull demonstrated decreased echoginicity (figure 1). The visualization of intracranial structures was increased, due to poor mineralization. The limb bones were extremely short and curved with fractures (figure 2). The chest appeared narrow and bell-shaped (figure 3) with short and irregular ribs (figure 4). Both lungs appeared hypoplastic. The spine and the abdomen were morphologically normal. Post natal X-ray examination (figure 5) showed skeleton poor mineralization, confirming antenatal ultrasound data. At autopsy, the fetus weighed 78 grams. The skull was large, soft and poorly calcified with widely open fontanelles. The limbs were distorted and short. The chest was narrow, with short and fractured ribs, the lungs were small (figure 6). The sclerae were blue.

Discussion

Osteogenesis imperfecta (OI), also known as "brittle bone disease", is a genetic disorder characterized by increased bone fragility and decreased bone density, due to type I collagen quantitative and/or qualitative abnormalities [1, 2]. It is a rare affection that occurs in 1 out of 20,000 to 30,000 live births [3], with equal frequency among males and females, racial and ethnic groups. Severity and age at onset widely vary from severe forms lethal in perinatal period to mild forms diagnosed much later in life. The most widely used classification for OI distinguishes four types, based on clinical findings and disease severity, type II is the most severe form with perinatal death [4]. It can be diagnosed by ultrasound from 14 weeks of gestation [5], on specific signs such as intra-uterine growth retardation or hydramnios. Otherwise, examination may show abnormalities of skull, ribs, spine or limbs: decreased echogenicity due to insufficient mineralization, deformities related to fractures, callus formation, increased bone plasticity and micromelia, especially of the femur [6, 7]. It is difficult to make sure of the diagnosis, as severe OI and other lethal skeletal dysplasias such as achondrogenesis and hypophosphatemia have similar ultrasound signs.
In case of doubt and when termination of pregnancy is considered, low-dose computed tomography (CT) with three-dimensional reconstructions of the hole fetal skeleton can be performed after 26 weeks of gestation. CT is an efficient tool for specific skeletal dysplasia diagnosis. It is especially effective in confirming or excluding bone fractures, recognizing wormian bones and for a complete evaluation of the fetal spine. The role of MRI is limited, except when visualization of the fetal brain or visceral organs is required to look for associated abnormalities or to assess fetal lung volume. In our case, on the basis of the US findings and of the poor prognosis, the pregnancy was terminated.
At birth, infants with OI type II have very short curved limbs, long bones fractures, narrow chest and soft skull. The sclerae are usually blue or gray. The radiologic features are characteristic and include absent or poor mineralization, flat vertebral bodies, very short broad femurs, broad short ribs in "bamboo"[8]. OI type II is uniformly lethal in the perinatal period. The usual cause of death is severe respiratory insufficiency due to pulmonary hypoplasia [9].

Differential Diagnosis List

Final Diagnosis

Osteogenesis imperfecta type II

URL:	https://www.eurorad.org/case/13376
DOI:	10.1594/EURORAD/CASE.13376
ISSN:	1563-4086