Spondyloepiphyseal Dysplasia.
Spondyloepiphyseal dysplasia (SED) is a descriptive term for a group of disorders with primary involvement of the vertebrae and epiphyseal centers resulting in a short-trunk disproportionate dwarfism. Spondylo refers to spine, epiphyseal refers to the growing ends of bones, and dysplasia refers to abnormal growth. Two major types of SED are recognized, namely, SED congenita and SED tarda.
Imaging Studies:
Radiographic imaging in patients with SED congenita: According to Spranger and Langer (1970), a complete skeletal survey is warranted in the initial assessment. This includes anteroposterior and lateral skull, cervical skull with anteroposterior, open mouth, and lateral views in flexion, neutral, and extension; posteroanterior views of the wrist and hand; anteroposterior and lateral projections of the elbows, hips, and knees; anteroposterior and lateral views of the thoracolumbar vertebrae; and an anteroposterior film of the lumbar and sacral regions .
Radiographic imaging in patients with SED congenita: According to Spranger and Langer (1970), a complete skeletal survey is warranted in the initial assessment. This includes anteroposterior and lateral skull, cervical skull with anteroposterior, open mouth, and lateral views in flexion, neutral, and extension; posteroanterior views of the wrist and hand; anteroposterior and lateral projections of the elbows, hips, and knees; anteroposterior and lateral views of the thoracolumbar vertebrae; and an anteroposterior film of the lumbar and sacral regions .
- A generalized delay occurs in the development of ossification centers. The epiphyseal centers of the distal femur and proximal tibia, os pubis, calcaneus, and talus, which are usually present at birth, are absent in these patients. The femoral heads may not be apparent on radiographs until patients are aged 5 years. When the epiphyses do appear, they are flattened and irregular in shape.
- Varying degrees of platyspondyly are present, with posterior wedging of vertebral bodies giving rise to oval, trapezoid, or pear-shaped vertebrae. The ossification of the bodies may be incompletely fused, as depicted in frontal projection. In adolescents and young adults, end plate irregularities and narrowed intervertebral disk spaces become obvious with an increased anteroposterior diameter of the vertebral bodies. Lumbar lordosis is usually exaggerated. Progressive kyphoscoliosis may develop in late childhood. The most marked abnormality is usually at the thoracolumbar junction, where gross ventral hypoplasia may be present.
- Skull examination may reveal a steep anterior base, with the angle between the floor of the anterior fossa and clivus reaching up to 165° (compared to 110-145° in healthy individuals). Odontoid hypoplasia or os odontoideum leading to atlantoaxial instability is common. Flexion-extension lateral cervical radiographs may reveal anterior, posterior, or anteroposterior instability. The thorax is broad and bell-shaped , and the ribs may flare at the anterior ends. The costovertebral angles are increased, and the intercostal spaces are narrow.
- The iliac crests are short and small, with horizontal acetabular roofs and delayed ossification of the pubis. The iliac bones are small in their cephalocaudad dimension, with lack of normal flaring of the iliac wings. The Y cartilage is wide. The acetabular fossae are deep and appear empty due to the severely retarded ossification of femoral heads. Coxa vara of varying severity is almost present .
- In patients with severe coxa vara, progressive varus deformity may occur, leading to discontinuity of the femoral neck and proximal migration of the greater trochanter. The femoral shafts ride high under the iliac wings, and pseudoarticulation of the greater trochanters with the lateral margins of iliac crest is suggested.
- The delayed ossification of the femoral head predisposes the hip to deformation with flattening, lateral extrusion, hinge abduction, and premature osteoarthritis. Ossification of the femoral head and neck proceeds slowly, frequently from multiple foci. The metaphyseal line of ossification frequently has a mottled appearance, and the femoral heads appear mottled and granular.
- The ossification centers of the distal femur and proximal tibia are delayed, leading to flattening and irregularity. Genu valgum is usually present, with overgrowth of the medial femoral condyle. Mild flaring of the metaphyses of long tubular bones may be present, along with irregular ossification from alterations in endochondral bone formation. Full-length radiographs of the lower extremity may be indicated to depict the overall alignment before surgical procedures of the hip or knee.
- The long tubular bones are relatively short and broad. Some metaphyseal flaring is present, especially in the region of the distal femur and proximal and distal humerus. The short tubular bones of the hands and feet are minimally broadened and shortened. Ossification of carpal and tarsal centers is usually delayed or disorganized, with occasional extra epiphyses. Wynne-Davies reported on the appearance of an epiphysis at the base of the second metacarpal, first seen in the patient at age 1-2 years.