Congenital Ventral Abdominal Wall Defects (Omphalocele): Safely Inducing Skin Growth

An omphalocele is a congenital abdominal wall defect consisting of an amnion covered sac containing the abdominal organs. This defect may occur spontaneously or be a factor of autosomal dominant inheritance. An omphalocele results when the intestines fail to return to the abdominal cavity after normal embryonic herniation into the umbilical cord during weeks 6 through 10 of development and is typically attributed to a folding defect in the abdominal wall rather than to the genes involved in gut elongation and rotation.
   

An omphalocele occurs in 1 out of approximately every 4000 live births in the United States and is classified as small (<4 cm in diameter), giant(>6–8 cm in any dimension), or ruptured. An omphalocele sac consists of the covering layers of the umbilical cord, which include amnion, Wharton’s jelly, and peritoneum. Varying amounts of bowel may be contained within the omphalocele sac, along with other intra-abdominal viscera, including liver, bladder, stomach, ovary, and testes. The umbilical cord is attached to the sac itself. A giant omphalocele (GO) contains abdominal visceral contents as well as parts of liver (see Figure 1)^1-3; it occurs in 1 in 10 000 live births. Mortality is related to its size and associated anomalies.

Prenatally, an omphalocele can be suspected as one of the causes of elevated maternal serum alpha-fetoprotein; ultrasound in the second trimester can capture the defect. A prenatal diagnosis of omphalocele should be followed by a comprehensive fetal ultrasound, including fetal echocardiography, because an omphalocele is accompanied by an up to 25% incidence of cardiac anomalies.¹ Pulmonary hypoplasia also is commonly associated with an omphalocele and may result in early respiratory distress, requiring intubation and ventilatory support at the time of delivery. Associated syndromes such as cloacal exstrophy, Donnaié Barrow syndrome, and pentalogy of Cantrell also can be suggested by fetal ultrasound. Chromosomal abnormalities, most commonly trisomies 13, 18, and 21, occur in up to 50% of fetuses diagnosed with an omphalocele.^1,2 Association with Beckwith-Wiedemann syndrome and anal, cardiac, tracheoesophogeal fistula, renal, and limb malformations also should be considered.

The risk of a chromosomal abnormality appears to be more common in fetuses with a central omphalocele than those with epigastric omphaloceles. Among fetuses with normal karyotypes, nearly 80% have multiple additional anomalies including cardiac, gastrointestinal, urologic, musculoskeletal, renal, and neurologic system disorders.^1,2 Interestingly, multiple associated anomalies appear to be more common with smaller omphaloceles than GOs, with anamoly rates of 55% versus 36%, respectively. Cardiac defects are the most common anomalies in this group.

Closing a GO is challenging. Small defects can be closed primarily or with a patch; a GO requires gradual reduction secondary to severe abdominovisceral disproportion. Despite advances, the mortality rate of GO can be up to 25%, and no optimal technique of closure has been established.³ Before 1900, an aggressive surgical approach was utilized, often with poor outcomes due to accompanying comorbidities and abdominovisceral disproportion.³

Escharotic therapy, which results in gradual epithelialization of the omphalocele sac, is a form of staged closure that can be used for neonates who cannot tolerate surgery due to prematurity, pulmonary hypoplasia, congenital heart disease, or other anomalies. Granulation and epithelialization of the sac using escharotic therapy usually takes many months. Once epithelialization has occurred and the infant is stable enough to endure anesthesia and surgery, the remaining ventral hernia can be surgically repaired; this usually requires use of prosthetic mesh with skin flap coverage, especially at the upper end of the defect. Tissue expanders have been used at this stage as well as in the neonatal period to create an abdominal cavity big enough to house the viscera.

The first reports of alcohol and mercurochrome application to promote cicatrization of the sac were published in 1899, leading to the “paint and wait” approach (see Figure 2).^4,5 Alcohol quickly fell out of favor due to frequent reports of alcohol intoxication.5 Mercurochrome was commonly used in 1960 for escharotic therapy and disinfection; however, this treatment option was abandoned after reports of deaths due to mercury poisoning.⁵  Povidone-iodine also has been used; systemic absorption of the iodine component during the initial therapy has been associated with transient hypothyroidism. Absorption is negligible after escharotic therapy, but thyroid function should be monitored in infants treated with povidone-iodine. The potential for hypothyroidism has led to decline in the use of povidone. Manuka honey recently has been used successfully, but few reports are available.

Silver sulfadiazine is the most common topical applicant currently in use.^4,5 Once initial cicatrization has begun, silver sulfadiazine may be exchanged for an absorbent synthetic fiber such as Aquacel Ag (ConvaTec) to keep the scarred sac dry while epithelialization gradually occurs. Various regimens are suggested — some suggest twice-daily and some (more commonly) recommend once-daily application initially and then once every 2 days when the cicatrization appears imminent. Potential side effects of systemic silver absorption include argyria, leukopenia, peripheral neuropathy, ocular abnormalities, hyperbilirubinemia, methemoglobinemia, hemolysis in those with G6PD deficiency, decreased seizure threshold, nephrotic syndrome, and elevated liver  enzymes.^4-8 [Author’s note: it is important to underline potential side effects of silver, although I am not aware of reports of patients with omphalocele developing side effects from the silver sulfadiazine cream.] The cream application can cause local allergic reaction, be time- and personnel-consuming, cause patient discomfort, and lead to expected silver-related black discoloration, at times liquefying and overspreading the abdominal area in a preterm infant confined to a humidified warm isolette.

Kerlix (Tyco Healthcare) is the most common secondary dressing utilized. Kerlix can be challenging to apply multiple times circumferentially, causing decompensation in  many babies who are unstable secondary to respiratory and cardiac conditions. In addition, the inner layers of the dressing absorb a significant amount of ointment, requiring frequent reapplication. Many clinicians apply an elastic bandage over the dressing to support the structure and limit skin laxity.

Case reports and series regarding various silver-impregnated dressings have populated surgical and wound literature as an alternative to silver sulfadiazine.^6-8 Silver-impregnated nanocrystalline dressings and hydrofiber impregnated with silver have offered positive results by completing escharotic therapy without daily dressing changes (thus requiring less personnel), skin discoloration, and most importantly much less systemic absorption while still delivering antimicrobial coverage when a moist covering and enhanced autolytic debridement are provided. Most practitioners describe dressing changes every 3 to 7 days. The typical hard necrotic black eschar seen with silver sulfadiazine usually is not observed; instead, a dark yellow-green/tan to black softer shell forms (see Figure 3). Published reports note the positive outcomes of infrequent dressing changes, not only in terms of avoidance of systemic toxicity, decreased resources, and patient comfort, but also in improved wound bed care because less exposure to low temperature mitigates decreased macrophage/neutrophil activity until normal temperature is restored (which may take up to 7 hours) — that is, once the wound bed is exposed to low room/outside temperatures, the physiologic functions of fibroblasts and macrophages slows down, which slows epithelialization. Less frequent wound bed opening promotes faster healing. Clinicians who have used hydrofiber material have commented on enhanced debridement of omphalocele slough, while ensuring a moist and antimicrobial wound bed, decreased sac injury/maceration, and similar time to complete epithelialization compared to silver-containing cream.^6-8

Concomitantly, surgical options for the final closure include creation of skin flaps, the component separation technique, negative pressure wound therapy, and intra-abdominal tissue expansion.³ Staged closure requires a slow progression, which can be hindered by inadequate tissue expansion, infection, respiratory compromise due to pressure from the abdominal cavity; once closed, potential problems include surgical closure dehiscence, loss of tissue, bowel content evisceration, sepsis, and prolonged hospitalization.³

In my practice, we are using a new silver-impregnated hydrofiber dressing (Aquacel Ag Extra). This dressing is composed of 2 layers of hydrofiber, delivering greater absorbency and more support and structure to a potentially pedunculated and large omphalocele. As it is exuded, released silver is thought to be bound by chloride in the exudate but continues to provide antimicrobial coverage. We change dressings every 3 to 6 days. Normal saline is used to moisten the dressing slightly to allow intimate contact with the amnion covering. Petrolatum-impregnated gauze is placed on top to avoid drying. Side support and stabilization is provided by cutting out the middle portion of the silver-infused hydrofiber surgical dressing (see Figure 4). Soft hydrofiber provides a cushioned barrier dressing and superior structural support to the soft defect (see Figure 5). Lobulated defects with deep crevices can be managed by applying silver ointment to the deeper crevices. In our experience, omphaloceles epithelialize fully in 3 months.

Because the potential side effects of prolonged silver sulfadiazine use were of concern, we are pleased the new silver-impregnated hydrofiber technology offers a feasible choice in managing GOs using escharotic therapy and the resolution of a concerning issue in our patients.