Streeter Dysplasia 

Streeter dysplasia is a term used to describe a complex disorder characterized by constricting rings (see image below), acrosyndactyly, or, often, amputations of the extremities of neonates. It is analogous to constriction band or amniotic band syndrome (ABS), which was recognized as early as 300 BC. Hippocrates suggested that extrinsic pressures from a ruptured amniotic membrane lead to the formation of bands or digital amputations. In 1652, J.B. van Helmont reported on intrauterine amputations, which he attributed to the pregnant mothers having looked upon maimed soldiers. Montgomery^[1] in 1832 and Simpson^[2] in 1836 subsequently described series of amniotic band–associated deformities and discussed the differences between agenesis- and amniotic band–induced amputations.

The term "Streeter dysplasia" did not come into use until 1930, when George Streeter postulated a germ plasm defect as one plausible etiology.^[3] At that time, his theory was well accepted because of the associated anomalies, which occurred far from the site of the constriction bands. In 1960, Patterson used histology to show how constriction bands looked like normal skin creases. He hypothesized that the same lack of mesodermal development occurs in the area of the band, thereby making the bands simply abnormal creases.^[4]

Patterson's theory was later refuted by Richard Torpin, who examined many placentae and infants with the disorder.^[5] In 1965, he reintroduced the idea originally held by Hippocrates. He proposed that maternal trauma led to rupture of the amniotic membrane, which then formed into strands. These encircling strands cause extrinsic compression on the head or limb, leading to the formation of bands, vascular occlusion, and, eventually, amputations. Currently, this is the most widely supported hypothesis; therefore, this disorder would be more accurately termed ABS.

Depending on the severity of the constriction, the defect could be as minimal as a merely cosmetic band. Deeper bands may cause lymphatic obstruction leading to edema and vascular compromise that necessitates immediate release. Pressure from the bands may potentially cause abnormalities distal to the constriction, such as hemihypertrophy, anterolateral bowing, pseudarthrosis, leg-length discrepancy, and resistant teratologic clubfeet. These conditions may lead to limited function and difficulty with ambulation.^[6]

Constriction bands across the head and face may lead to facial clefts. If the cleft extends into the cranium, encephaloceles may result. Bands that cross the body may compromise the chest (thoracoschisis or extrathoracic heart) or abdomen (gastroschisis).

Frequency

The estimated frequency of amniotic band syndrome in the United States is 1 per 3000 pregnancies (if the potential miscarriages that occur from severe banding early in gestation are considered). More common statistics show an incidence of 1 case per 10,000-15,000 population. One of the few epidemiologic studies is a 1988 study from Atlanta that cites the incidence as 1.16 cases per 10,000 population. No sex predilection is recognized.

The incidence overseas is similar to that in the United States. The birth defect registry of Western Australia cites an incidence of 1.15 per 10,000 population.

Two main lines of thought exist regarding the etiology of amniotic band syndrome, attributing the condition to intrinsic and extrinsic causes. Streeter proposed that a disruptive event occurs during blastogenesis, leading to an intrinsic germ plasm defect.^[3] This causes the soft tissue to slough. External healing of the slough leads to the constricting rings and the resultant localized developmental defects. Cases of ABS in which the amnion is intact support this theory, as do the frequently associated renal abnormalities (37% of cases) and occasional cardiac abnormalities.

Ainhum, a predominantly African syndrome in which progressive circumferential ulceration leads to eventual amputation of digits, is an inherited disease, thus further lending support to an intrinsic developmental defect as a cause of digit amputation. Streeter aggressively defended this theory for more than 35 years. For his long and avid support, many surgeons still describe this disorder as Streeter dysplasia.

The lack of family history or predictable recurrences in families of children born with ABS negates the theory of an inherent or genetic component to the condition. Zionts and coworkers^[7] were able to demonstrate variable findings of the syndrome in monozygotic twins who each were affected by amniotic bands. These and other sporadic findings are more consistent with the current thought that external compression is the etiologic root of this syndrome.^[8]

In 1965, Richard Torpin reintroduced the extrinsic theory for ABS.^[5] In his study of fetuses and placentae, he noted the lack of a complete amniotic lining in the placentae of neonates with ABS. Strands of amnion were also visible around constricting rings of the digits, and binding strands were visible at the tips of limbs with acrosyndactyly. He proposed that intrauterine trauma led to premature rupture of the membranes, and strands of residual membranes could encircle the digits or might even be swallowed. The presence of severed but otherwise fully developed limbs in newborn infants further validates this extrinsic band compression theory.

The developing embryo sits within 2 cavities: the amnion and the chorion. As development occurs, the amnion presses against the extracoelomic space, eventually obliterating it and bringing the amnion up to and supported by the chorion. This phenomenon occurs on or about the 12th week of gestation. Incomplete obliteration of the extracoelomic space renders the amnion fragile and subject to spontaneous or traumatic rupture.^[9] After the rupture, a transient oligohydramnios occurs due to extravasation of amniotic fluid. Until the chorion adjusts to the permeability, the developing fetus has very little room in which to move. This may contribute to the severity of clubfeet deformities seen with ABS.

This decrease in space also allows the resultant floating amniotic bands to easily ensnare a developing body part. Early in gestation, the encircling bands may result in spontaneous abortions. If the constriction occurs after development is nearly complete, only fissures, acrosyndactylization, and/or intrauterine amputation are noted on the extremities as typical manifestations. If the amniotic bands are swallowed while still partially attached to the placenta, the tether may lead to bizarre facial clefts and palate deficiencies.^[10]

Children born with amniotic band syndrome are usually full term or a few weeks premature; in most cases, the pregnancies were uncomplicated. In Light and Ogden's series, the average gestation was 37.5 weeks, with an average birth weight of 3.0 kg.^[11] Although the condition is quite variable in presentation, the most common clinical findings in ABS appear on the extremities and include amputation followed by constriction bands and then acrosyndactyly. Other associated findings include encephalocele, cleft lip or palate, renal abnormalities, cardiac defects, hemihypertrophy, anterolateral bowing of the tibia, tibial pseudarthrosis,^{[12, 13]} and leg-length discrepancy.

On the extremities, the distal portion is most often involved, especially the longer central digits of the hand (middle, long, and index fingers). The hands are affected in almost 90% of cases.^[14] In rare cases, the thumb or small finger is involved, presumably because of their shorter lengths. The same rule holds true for the feet, where constriction bands most commonly involve the hallux. Mild band pressure causes only indentations at the base of the phalanx, usually distal to the metacarpophalangeal joints. Progressive constriction is the result of the maceration of the indentation and subsequent healing by scar tissue formation. If the compression from the band is severe, lymphatic and vascular compromise may ensue, and the child presents at birth with a swollen engorged digit or limb that may require immediate surgical release.^[15]

More commonly, the digit has been amputated in utero. Acrosyndactyly occurs after digital separation is complete, but the fingers get twisted by bands and eventually coalesce. The peripheral digits are brought forward, and residual sinus tracts are usually present in the remnant web space where a probe can be placed—so-called fenestrated syndactyly.

Extremity deformities in ABS are classified into Patterson's 4 types, as follows:

• Type I involves simple ring constriction.
• Type II involves ring constriction accompanied by fusion of the distal bony parts, with or without lymphedema.
• Type III involves ring constrictions accompanied by fusion of soft tissue parts.
• Type IV demonstrates intrauterine amputations.

Clubfoot is seen in up to 25% of cases. This is a mix of paralytic and idiopathic deformities. In 50% of clubfoot cases, a tight band is found around the peroneal nerve, which causes muscle imbalance and clubfoot.^{[16, 17]} In the other 50%, no bands are visible anywhere on the limb. The deformity is thought to arise from lack of space due to oligohydramnios. The clubfoot deformity is typically rigid. Clinically significant limb-length discrepancy may also be present, and patients need to be sequentially monitored, even following correction of bands and the clubfoot. Other less common findings include craniofacial abnormalities, which may occur in up to 5% of ABS cases; acquired raised limb bands; and anterolateral bowing of the tibia with pseudarthrosis.

Indications for intervention depend on the medical stability of the child and on the neurovascular status of the limb. Anencephaly usually is incompatible with life, but the other deformities can be triaged for correction and reconstruction. Of all the deformities, only the tight constriction bands with gross lymphedema, vascular compromise, or both necessitate immediate surgical release.

Clubfeet should be manipulated and put in casts early, as is the case for all idiopathic clubfeet. The paralytic feet in ABS, however, usually are severe and do not respond well to conventional treatment. Surgical correction is also associated with a high incidence of recurrence and complications due to neurovascular injury from proximal bands over the peroneal nerve.

Cleft lip and palate require reconstruction, but this is optimal when the child is aged approximately 3-6 months, depending on the severity of the cleft and the infant's ability to feed.

The anatomy relevant to surgery depends on the area of the body affected. Most bands are superficial, and only the skin and subcutaneous tissue are involved. However, the neurovascular bundle may be displaced near areas of banding. Therefore, take this into consideration with dissection for excision in order to avoid devascularization or denervation of the involved body segments.

Mild bands that only cosmetically affect the superficial skin, similar to the creases found in the Michelin tire baby syndrome (circumferential-ringed creases with specific histologic findings and/or karyotype abnormalities), do not require any intervention. As growth occurs, progressive constriction and edema may necessitate band excision and Z-plasty, but in general, excision is not indicated for superficial bands due to the potential complications of wound infections and neurovascular compromise.