Musculoskeletal systemCase Type
Dr. Akshay Pendkar, 3rd year Radiology resident; Dr. Ketan Rathod M.D., Assistant Professor; Dr. H.P.Parekh M.D., Professor; Dr. N.U.Bahri M.D., Professor and Head.Patient
24 years, female
A 24-year-old female patient, primigravida, reported to the obstetric department with chief complaints of amenorrhoea for 5 months (22 weeks), abdominal pain with generalised weakness. She was an unbooked case and had no antenatal examination or investigation in her present pregnancy.
A single live intrauterine fetus with a head that is somewhat larger than rest of the body, corresponding to 21 weeks 4 days (Fig 1, 3). Adequate mineralisation of fetal bones was noted. Fetal head was not compressible. Fetal nose, lips and tongue were normal.
Fetal nuchal fold thickness was increased and measured 13.7 mm (Fig 1).
Fetal thorax was extremely narrow (transthoracic diameter: 11.3 cm) with thoraco/ abdominal ratio measuring 0.73 (Fig 2), femur length / abdominal ratio measuring 0.05, suggestive of pulmonary hypoplasia.
Fetal abdomen was relatively large and lax. (Abdominal circumference: 15.7 cm) (Fig 1, 2). Mild fetal ascites and excessively flat vertebral bodies were also noted.
Fetal limbs were extremely short and thick with femur, humerus, tibia and radius corresponding to 14 weeks and 1 day of gestation (Fig 4, 5). Telephone handle appearance of femur was noted (Fig 6). Clavicle was normal. There was no club foot or rocker bottom foot (Fig 7).
Thanatophoric dysplasia is the most common lethal skeletal dysplasia . It belongs to the group of chondrodysplasias . Its incidence is between 1/6000 to 1/17000 births . Thanatophoric dysplasia is an autosomal dominant disorder which is caused due to specific mutation in Fibroblast growth factor receptor 3 located on the short arm of chromosome 4 . It is of two types, type I and type II. Type I Thanatophoric dysplasia has disproportionate dwarfism with very short bowed extremities that gives rise to a telephone handle appearance of femur, more severe platyspondyly, normal trunk length with severely narrowed thorax, macrocephaly, depressed nasal bridge, frontal bone bossing with proptosis . Type II Thanatophoric dysplasia has characteristic skull deformity, known as cloverleaf skull due to premature fusion of all the skull sutures. The shortened extremities may be straight, platyspondyly is less severe in type II Thanatophoric dysplasia . Polyhydramnios is present in 50 % of the cases of both, type I and type II thanatophoric dysplasia . Cause of death in most cases is respiratory failure due to pulmonary hypoplasia . Antenatal diagnosis is made with the following features seen during second trimester scan: severe rhizomelia with bowing, narrow thoracic cavity (cardiac circumference > 60% of thoracic circumference), lax abdomen, loose abdominal skin, cloverleaf skull (trilobed skull) . Associations: Cardiac anomalies, renal anomalies, corpus callosum agenesis with ventriculomegaly and radioulnar synostosis . Radiographic features of thanatophoric dysplasia are severe micromelia with bowed extremities, large skull, narrow bell shaped chest with short ribs, reduction in interpediculate distance of the last few lumbar vertebrae, small, square iliac wings, narrow sacrosciatic notch, horizontal acetabular roof .
Since it is a lethal skeletal dysplasia, the only option feasible is termination of pregnancy as an when correct diagnosis has been made .
Take home message:
Severe rhizomelic type of micromelia associated with bowing of long bones giving telephone handle appearance of femur, narrowed chest, cloverleaf skull associated with relatively normal mineralisation of fetal bones, raise the suspicion of Thanatophoric dysplasia whose correct diagnosis is very important, since it is a lethal skeletal dysplasia, where the most common cause of death is pulmonary hypoplasia.
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