Focal Growth Disturbances

Etiology

Teratogenic factors due to drugs taken during pregnancy are the best known cause of focal growth disturbances (e.g., thalidomide-associated phocomelia), but sporadic cases of unknown cause are now more frequent. This is due principally to the greater precautions taken in prescribing medications during pregnancy.

Sporadic cases with focal growth disturbances may be due to somatic mutations in genes that regulate growth and cell division. The advent of new genetic technologies, such as next-generation sequencing, now allows us to identify these genetic defects in somatic tissues.

Prevalence and Epidemiology

Fortunately, focal limb disturbances are very rare. The prevalence varies from disease to disease.

Clinical Presentation

Focal malformations of the limbs include absence of bone, hypoplastic bones, segmentation anomalies (such as fusion), abnormal bowing, or hypertrophy of bones.

They may be associated with abnormalities of other organ systems in the direct surroundings of the abnormal bone, such as the skin, heart, abdominal viscera, or central nervous system.

Pathophysiology

The embryologic limb buds appear bilaterally at about the 26th day of gestation at Wolff crest ( eFig. 101-1 ). By the 30th day, the upper limb has started differentiating into three segments (upper arm, forearm, and hand), and in the lower limb, the same process occurs shortly afterward. By the end of the sixth gestational week, the embryo has acquired a recognizable human form. Therefore, most congenital anomalies occur in the third through seventh weeks, when the tissues are rapidly developing. After the seventh week, certain types of insult may still result in limb anomalies because the upper limb is only fully formed by 12 weeks' gestation and the lower limb by 14 weeks' gestation.

eFIGURE 101-1, Schematic drawing of the embryologic limb buds at Wolff crest. 1, Upper limb bud; 2, lower limb bud.

Imaging Techniques

Techniques and Relevant Aspects

Defects in limb formation are most often recognized by ultrasound examination during pregnancy. After birth, conventional radiography remains the “gold standard” for assessment of focal growth anomalies. Ultrasonography and MRI may be useful in delineating unossified cartilage or associated soft tissue abnormalities.

Manifestations of the Disease

Various classification systems of limb deficiencies have been proposed, but none is completely satisfactory. Some of them are very complex and are therefore difficult to use in routine daily practice. For the sake of simplicity, congenital focal growth anomalies are classified here based on the number of bones (absence vs. extra bones), morphology (hypoplasia, bowing), segmentation, and location (upper vs. lower limb). Only the most common and clinically important entities are discussed in this chapter. Unusual and atypical cases may be analyzed with the more detailed texts described in Suggested Readings.

Absent or Hypoplastic Bones (Deficiency)

Amelia refers to a complete absence of a free limb (exclusive of girdle). Meromelia refers to the partial absence of a free limb. The descriptive terms phocomelia, peromelia, dysmelia, ectromelia, and hemimelia have been eliminated from the terminology. Transverse deficiency is used when the absence extends across the full width of the limb. Longitudinal deficiency is used when the absence extends parallel with the long axis of the limb, involving preaxial, postaxial, or central components of the limb.

Glenoid Hypoplasia

Glenoid hypoplasia or dysplasia of the scapular neck is a congenital anomaly characterized by an ossification failure of the lower two thirds of the glenoid and adjacent scapula.

Radiographic Findings

The usual radiographic findings consist of hypoplasia of the scapular neck with a typical dentate or notched appearance of the articular surface of the glenoid. The inferior glenohumeral joint is usually widened. Additional findings may include hypoplasia of the humeral neck and head, varus deformity of the proximal portion of the humerus, and sometimes enlargement and bowing of the acromion and clavicle (see eFig. 101-2 ).

eFIGURE 101-2, Glenoid hypoplasia. The standard radiograph of the right shoulder shows a dentate articular surface of the glenoid and a decreased ossification of the scapular neck. The glenohumeral joint appears widened inferiorly, and there is slight hypoplasia of the humeral head.

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