Fig. 4: Radiograph at autopsy demonstrating marked disorganization of the vertebral bodies. See text for further description of bony deformities.
Radiographic findings at autopsy demonstrated marked vertebral disorganization, short humeri, and femurs with splayed metaphyses. Also noted was abnormal angulation of the bones of the distal extremities (fig. 3 right).
The antenatal diagnosis of short-limbed dwarfism is usually made in one of two clinical situations: the patient is referred for ultrasound secondary to a family history of dwarfism, or routine exam reveals a femur measuring less than the 5th percentile for gestational age. Rhizomelic dwarfism is characterized by shortening of proximal long bones; micromelic dwarfism, exemplified by dyssegmental dysplasia, reveals abnormalities in all bony structures.
Izquierdo1, Aleck2, and others have described the typical findings of dyssegmental dysplasia which include micromelic dwarfism, disorganization of vertebral bodies, cephalocele, small orbits, mid-facial flattening, cleft palate, short neck, elongated clavicles, and alterations in the size, shape and ossification of the acromion, coracoid process, and body of the scapulae. Usually present is the finding of hydroureter.
Aleck2 and others have described the less severe, although ultimately fatal form of dyssegmental dysplasia known as the Rolland-Desbuquois variety. Most affected infants survive the neonatal period, but succumb by the age of three years. This variety of the disease has not yet been described in the Hispanic population.
The differential diagnosis includes fibrochondrogenesis, chondrodysplasia punctata and Weissenbacher-Zweymuller syndrome.
Fibrochondrogenesis is characterized by limb and vertebral deformities including shortened dumbbell-shaped metaphyses and pear-shaped vertebral bodies3. The short limbs noted in fibrochondrogenesis are in a proximal or rhizomelic pattern. This is in contrast to dyssegmental dysplasia which is characterized by micromelia or disproportionate shortening of the entire extremity.
Chondrodysplasia punctata is typified by vertebral bodies with coronal clefts, metaphyseal splaying and stippled epiphyses. The ultrasound diagnosis is reported elsewhere in this issue3, and the rhizomelic, potentially lethal variety has been diagnosed using radiography4.
The final diagnosis of short-limb dwarfism often requires analysis of the pathologic specimen. For example, scanning electron microscopy has been used to demonstrate that growth plate morphology, cartilage calcification, bone morphology and collagen within resting cartilage are all more extensively abnormal in the Silverman-Handmaker form of the disease than in the Rolland-Desbuquois variety2.
1.Izquierdo LA, Kushnir O, et al. Antenatal ultrasonic diagnosis of dyssegmental dysplasia: a case report. Prenatal Diagnosis (in press)
2.Aleck KA, Grix A, et al. Dyssegmental dysplasias: clinical, radiographic, and morphologic evidence of heterogeneity. Am J Med Genetics 27:295-312, 1987
3. Furness ME, Haan EA, Hopkins PB et al: Chondrodysplasia punctata, mild symmetric type with echogenic coccyx in a 15 week fetus. The Fetus 1:1 7565-1, 1991
4. Romero R, Pilu G, Jeanty P, et al: Prenatal diagnosis of congenital anomalies. Norwalk, Connecticut: Appleton & Lange, 1988, pp 339-340; 349-351