Address correspondence to: Margaret E. Furness, FRACR, DDU, Women"s Victoria Hospital, 160 Fullarton Road, Rose Park,South Australia 5067 Ph: 61-8-333-9105; Fax: 61-8-333-9184

MESH Foot deformities, congenital ICD9 754.7 CDC 754.780

Introduction

Fetal feet can contribute useful information in fetuses at risk for a particular condition, or where other abnormalities have been identified. Some of the appearances demonstrated in this collection are “soft” signs of abnormality (i.e., as isolated findings, do not warrant karyotyping), since they can also be normal variants. If one of the definite abnormalities is identified, lists of differential diagnoses should be sought in major textbooks^1-5 or databases.

Material & methods

Images were obtained at 17-18 weeks" gestation, unless otherwise stated.

Findings

Sandal gap

A gap between the first and second toes (fig.1), as a minor anomaly^4,5, is only a soft marker for trisomy 21³, since a similar appearance can be produced by abduction. Abduction of the first toe with a short metatarsal can occur in trisomy 18⁶. A broad first toe may be a useful marker in families with certain syndromes, e.g. acroce­pha­losyndactyly, Type V (BDE 2284).

Figure 1: Sole of foot showing abduction of first toe. This normal fetus" father could pick up tennis balls with his toes.

Echogenic calcaneus

An echogenic focus in the heel is a normal finding after 17-18 weeks (fig. 2). Before this, it is a soft marker for chondrodysplasia punctata and related conditions⁶, and for aneuploidy (premature ossification in trisomy 21). Punctate calcification occurs in triploidy (fig. 3) and trisomy 18.

Figure 2: Echogenic focus in heel, sagittal view.

Figure 3: Lateral X-ray of triploid fetus, with punctate calcification in the heel.

Rockerbottom foot

The rockerbottom foot, with a prominent heel and convex sole (fig. 4, 5) occurs in trisomy 18, ­18q-¹, and triploidy. Karyotyping may be best reserved for those which are definitely abnormal, rather than merely suspicious. Note that orthopedic surgeons use the term "rockerbottom foot†for two other conditions, vertical talus and overtreated talipes.

Figure 4: Rockerbottom foot, sagittal view. Note prominent heel. Triploidy. 

Figure 5: Lateral X-ray, rockerbottom foot. 

Talipes

Abnormal foot posture occurs in bone dysplasias; in deformations most commonly due to oligohydramnios; as part of many primary malformation syndromes; and in secondary malformations due to neuromuscular disease⁵. We suspect that it is a poor prognostic sign in spina bifida during the second trimester. The most common form is talipes equinovarus (fig. 6) in which there are various angulations of the heel, ankle equinus, and forefoot abduction and supination. Talipes equinus (fig. 7) is rare. The normal foot, however, can achieve startling degrees of dorsiflexion (fig. 8) and plantarflexion.
 

Figure 6: Bilateral talipes equinovarus (29 weeks, fetal dyskinesia sequence). Note varus angulation of forefoot.

Figure 7: Talipes equinus, 32 weeks. Mother and siblings had myotonic dystrophy. Top: sagittal. Bottom: coronal; the calf and sole are in the same plane. 

Figure 8: Normal dorsiflexion, 36 weeks, sagittal view.

Polydactyly

Polydactyly (fig. 9) cannot always be excluded by ultrasound scans, since the extra digit, in some cases is no more than a skin tag. Counting toes is not routine and rarely productive.

Figure 9: Polydactyly (familial, with polyhydramnios, 32 weeks). Arrowhead: extra digit.

Amputations

The early amnion rupture sequence (p 6588) can cause edema of an extremity distal to a constriction band (bilateral pedal edema is more likely to be syndromal or due to aneuploidy). It can also cause amputation of digits or extremities (fig. 10) or terminal syndactyly. Syndactyly of the toes is difficult to diagnose by ultrasound. Absent digits can occur in a wide range of conditions, including vascular causes, either occlusive or hypoxic (fig. 11). Absence of central digits is seen in the clawfoot (ectrodactyly) syndromes (fig.12). 
 

Figure 10: Early amnion rupture sequence. Left: edema of the foot (arrows). Right: amputation of the first toe (not recognized antenatally) (arrowhead). All four extremities showed amputations.

Figure 12: Split hand-foot syndrome. Note gap between the medial and (fused) lateral toes, clearly different from fig.1.

There is a spectrum ranging from partial absence of the 3^rd digit, to those which also have clefting of the foot or hand with syndactyly of the digits on each side, to those which have only the 5^th digit present. The most severe forms are usually bilateral, and about half of them have a family history⁵ (a number of syndromes are possible).

Hypoplasia of the foot

Varying degrees of hypoplasia of the foot and abnormality of the ankle joint occur with tibial hemimelia. This condition occurs in 100:10,000 live births. It may be isolated, usually as a new mutation, or part of a number of syndromes. 

Figure 13: Tibial hemimelia, 22 weeks (unilateral and isolated). F: femur, T: tibia; arrowhead, hypoplastic foot lying posterior to tibia.

Figure 14: Postnatal X-ray, same patient as fig.13. C: calcaneum.

Sirenomelia

The sirenomelia sequence (p. 7553-1) shows varying degrees of fusion of the lower limbs. The feet may be absent (apus), fused (monopus), or separate (dipus)⁷ (fig. 15). It is not clear whether it represents part of the caudal regression spectrum or is due to an alteration in early vascular development⁴. 

Figure 15: Sirenomelia, dipus form. Left: sagittal view of head (H) and body; the fused lower limb (arrows) lies posterior to the spine. Right: lower limb. F: femur; T: tibia; arrowheads: feet (which moved independently of each other). The fibulae were absent.

References

1. Romero R, Pilu G, Jeanty P, et al.: Prenatal diagnosis of congenital anomalies. Appleton & Lange, Norwalk, 1988 pp311-84.

2. Taybi H, Lachman RS: Radiology of syndromes, metabolic disorders and skeletal dysplasias. Year Book Medical Publishers, Chicago. 3rd ed. 1990, pp863-78.

3. Nyberg DA, Mahony BS, Pretorius DH: Diagnostic ultrasound of fetal anomalies. Text and atlas. Mosby Year Book, St. Louis 1990.

4. Jones KL: Smith"s recognizable patterns of human malformation. W.B. Saunders Co., Philadelphia. 4th ed., 1988.

5. Buyse ML (Ed): Birth defect encyclopedia. Blackwell, Cambridge, MA 1990.

6. Sanders RC: Atlas of ultrasonic artifacts and variants. Mosby - Year Book, St. Louis 2^nd ed., p5 1992.

7. Furness ME, Haan EA, Hopkins PB et al.: Chondrodysplasia punctata, mild symmetric type with echogenic coccyx in a 15 week fetus. The Fetus 7565-1, 1991.

8. Pomerleaus D, Gurmond P, Moyer F: Sirenomelia. Am J Dis Child 126:493-4,1973.