VACTERL association is clinically defined by the presence of a cluster of congenital malformations. As described above, most (but not all) clinicians and researchers require the presence of at least three component features, though some place more emphasis on certain component features [
7-
9,
11-
15,
19]. Importantly, there must be no clinical or laboratory-based evidence of an alternate diagnosis. The following is a discussion of the specific defining features of VACTERL association as the condition is most commonly described. However, it is important to note that the literature demonstrates a wide degree of interpretation in terms of how diagnostic criteria are defined and applied, and any patient with suspected VACTERL association deserves careful scrutiny.
In several studies, vertebral anomalies, which are commonly accompanied by rib anomalies, have been reported in approximately 60-80% of patients; interestingly, patients may have rib anomalies without vertebral anomalies [
7-
9,
13,
15,
20]. Vertebral anomalies typically include segmentation defects, such as hemivertebrae, "butterfly vertebrae", "wedge vertebrae" (the latter two descriptions refer to the shape of the dysplastic vertebrae), and vertebral fusions, supernumerary or absent vertebrae, and other forms of vertebral dysplasia. There is a wide degree of severity of reported vertebral malformations. Some patients require multiple, major operations for vertebral anomalies, while others may have subtle defects only detectable through careful scrutiny by an experienced clinician [
13,
21]. Abnormal spinal curvature due to underlying costovertebral anomalies is common. Clinical signs of scoliosis may be the first sign of vertebral anomalies if imaging studies are not performed when VACTERL association is first suspected [
22]. Of note, while patients with ARM may have dysplastic sacral vertebrae, whether or not these should be included as true vertebral malformations for the diagnosis of VACTERL association is unclear [
13,
21,
23]. In fact, while these latter patients are sometimes described as having VACTERL association (especially if a minor renal anomaly is present), such a diagnosis is controversial.
Imperforate anus/anal atresia as part of an ARM occurs in approximately 55-90% of patients [
7-
9,
13,
15]. A complete imperforate anus is often discovered in the immediate postnatal period, typically through routine examination or due to inability to measure the infant's temperature rectally. However, other forms with stenosis may appear anatomically normal on initial examination, and may clinically present later with signs of obstruction [
23]. (While beyond the scope of this paper, formal classification schemes of many of the malformations seen in VACTERL association, such as ARM and TEF are available; please see specific references for more details.) As with other malformations, some controversy exists in terms of diagnostic criteria. For example, some clinicians only allow a completely imperforate anus to be considered part of VACTERL association (though this author would argue that this is too narrow a view, and that some allowance should be made for a spectrum of severity).
In patients with imperforate anus, genitourinary (GU) anomalies are also common as part of the ARM, but GU anomalies may also occur in patients without imperforate anus or anal atresia. Overall, GU anomalies occur in up to 25% of patients with VACTERL association, and may be less obvious than imperforate anus, such as is the case with fistulae connecting the GU and anorectal tracts [
23,
24].
Cardiac malformations have been reported in approximately 40-80% of patients with VACTERL association [
9,
13,
15]. One explanation for the highly variable rates of cardiac malformations may have to do with ascertainment bias in certain studies. For example, studies using malformation registries tend to describe higher rates of cardiac malformations than studies based on children seen in genetics clinics, as severe cardiac malformations result in a high rate of mortality. It is important to point out that some statistically-based analyses argue that cardiac malformations should not be included in the diagnostic criteria, as they are not more common in patients with VACTERL association than in other disorders with multiple malformations [
7-
9]. Nevertheless, structural heart anomalies are common in VACTERL association, and may range from severe structural defects incompatible with life or necessitating several stages of challenging surgery, to subtle anatomic defects ascertained in adulthood only through participation in research studies, and which would not be expected to cause any medical issues [
13,
15,
22]. The category of cardiac defects raises another important point that might be applied to VACTERL association more generally: certain variants in isolation (such as patent ductus arteriosus or patent foramen ovale) should standardly be considered a normal, age-based finding rather than a component feature of VACTERL association, and researchers and clinicians must be careful not to apply diagnostic criteria carelessly.
A number of subtypes of tracheo-esophageal fistula (TEF) may occur, and may present with or without esophageal atresia. Overall, TEF occurs in approximately 50-80% of patients [
7-
9,
13,
15]. Early signs of TEF include polyhydramnios or absent gastric bubble recognized prenatally, inability to pass nasogastric tubes immediately postnatally, or choking/swallowing in infancy [
25]. TEF typically require surgery in the first few days of life, and later complications may occur as well, such as fistula recurrence, reactive-airway disease, and gastro-esophageal reflux [
22]. In addition to TEF, other pulmonary anomalies may co-occur; these may share a common structural anatomical cause with the TEF and/or cardiac anomalies [
16,
26-
29].
Like other malformations seen in VACTERL association, there can be a wide range of severity and type of renal anomalies, which can include unilateral renal agenesis (or bilateral in severe cases), horsehoe kidney, and cystic and/or dysplastic kidneys, sometimes accompanied by ureteral and GU anomalies [
15,
24]. Renal anomalies are reported in approximately 50-80% of patients [
8,
9,
13,
15]. As with cardiac malformations, some statistical analyses have suggested that renal anomalies should not be considered one of the defining component features, as they may only be associated with certain features such as ARM [
7-
9]. Unlike many other features of VACTERL association, which are relatively clinically obvious, renal anomalies may be less apparent unless careful imaging is performed. Diagnosing occult renal anomalies is especially important, as these malformations may result in significant morbidity [
30].
Finally, limb malformations have been reported in approximately 40-50% of patients [
7-
9,
15,
17]. While classically defined as radial anomalies, including thumb aplasia/hypoplasia, many other limb anomalies have been ascribed (perhaps erroneously) to VACTERL association, including polydactyly and lower limb anomalies. As with the other malformations, there is a wide range of the degree of severity of limb anomalies in affected patients. One must take care to consider whether the particular limb anomaly in question should be considered part of VACTERL association or be taken to be a sign of a similar disorder in the differential diagnosis.
While the above malformations are considered to be the core component features, many other malformations have been described in affected patients [
8,
9,
15,
31]. On review, some of these features are likely signs of other, similar disorders, such as the finding of craniosynostosis in patients with Baller-Gerold syndrome, or coloboma in patients with CHARGE syndrome [
13,
15,
19,
32,
33]. Clinicians should thus use these non-typical malformations as a clue in considering possible other conditions, and should be cautioned to look carefully at other organ systems that could aid in the differential diagnosis, such as by obtaining ophthalmologic and audiologic examinations (see Table ).
| Table 1Differential diagnosis: conditions with multiple features in common with VACTERL association. |
Special note should be made of the presence of a single umbilical artery, which is frequent in patients with VACTERL association (though the exact prevalence is difficult to estimate) [
31,
34]. This is an especially important antenatal finding, as it may be the first sign of the diagnosis (see the section on Antenatal diagnosis below).