Congenital adrenal hyperplasia (CAH)

This is a recessively inherited condition caused by an enzyme deficiency in the adrenal cortex. In the majority of patients the deficient enzyme is 21-hydroxylase. Clinically there is an accumulation of steroidal precursors proximal to the enzyme deficiency, with a resulting diversion into the androgen (therefore male) biosynthesis pathways. This results in virilization of females and early masculinization in males. In the majority, aldosterone cannot be synthesized, and some infants may present with severe salt wasting in the neonatal period which may be fatal. While the adrenal glands may be detectably enlarged in some, ultrasound plays little role in assessing the glands.² However, CAH is the most common cause of female pseudohermaphroditism, with female infants presenting with ambiguous genitalia. The role of ultrasound in these infants with ambiguous genitalia is to demonstrate the presence of internal female structures (uterus and ovaries). The uterus is occasionally associated with a small hydrometrocolpos, as the insertion of a vagina may be anomalous and narrowed, sometimes inserting into the urethra with a persistent urogenital sinus^3–5 (see Fig. 7.11).

Adrenal hemorrhage

Adrenal hemorrhage is a common cause of an abdominal mass in a neonate. This has been reported in the literature as sometimes occurring as an antenatal event, and the sonographic appearances postnatally often confirm this. Conditions which are associated with adrenal hemorrhage are hemoconcentration caused by shock, hypoxia, septicemia, birth trauma or stress, and this occurs particularly in infants of diabetic mothers.^6,7

Clinically the neonates present with a palpable abdominal mass, anemia due to the hemorrhage, jaundice, hypertension and, if the mass is large enough, vomiting and small bowel obstruction.

There is a common association with renal vein thrombosis, which must be actively excluded, and this is more commonly left sided because of the insertion of the left adrenal vein into the left renal vein. Bilateral adrenal hemorrhages can occur. Hemorrhages may be complicated by abscess formation.⁸

In older children adrenal hemorrhage is associated with meningococcal septicemia, trauma and anticoagulants.

Ultrasound appearances

The adrenal hemorrhage has differing appearances depending on when in the evolution of the hemorrhage the ultrasound examination is performed. In the early stages when there is fresh hemorrhage, the adrenal is enlarged and echogenic. As the blood starts to liquefy, the central area becomes increasingly hypoechoic with some internal echoes; this can take 1–2 weeks from the time of hemorrhage. In a short space of time the hemorrhage starts shrinking (Fig. 4.3) and may ultimately be left with a rim of calcification. On plain abdominal radiography this is typically triangular in shape.

Figure 4.3 Resolution of an adrenal hemorrhage. (A) Longitudinal sonogram of an old right adrenal hemorrhage. The adrenal is predominantly cystic with some internal echoes. (B) Longitudinal sonogram of the right adrenal 1 month later (between calipers) showing that it has shrunk in size considerably. Adrenal hemorrhages change in their appearances very quickly.

When an adrenal hemorrhage is found, the kidneys must be carefully scanned and measured and the echogenicity evaluated for renal vein thrombosis. The features to look for are an echogenic enlarged swollen kidney with the typical increase in echogenicity of the interlobular vessels (Fig. 4.4).⁹

Figure 4.4 Adrenal hemorrhage and renal vein thrombosis. (A) & (B) Longitudinal and transverse sonogram on a large left cystic adrenal above the left kidney. This is the appearance of an adrenal hemorrhage which has liquefied. The kidney also appears abnormally swollen, with a patchy echo nephrogram and ill-defined bright interlobular vessels (arrow). This was an adrenal hemorrhage in association with renal venous thrombosis. This association is more common on the left, because of the drainage of the left adrenal vein into the left renal vein.

A much rarer condition, neuroblastoma, is the main differential diagnosis. Normally a neuroblastoma is more solid in appearance and will not change its internal echo texture with time. Serial examination is therefore recommended in the uncertain cases. However, urinary catecholamines (VMAs) will be elevated in over 90% of patients with neuroblastoma. Neuroblastoma may also undergo hemorrhage and be cystic in appearance.¹⁰ This coexistence with neuroblastoma may require further cross-sectional imaging, and it is in these instances that an MRI scan may improve diagnostic accuracy. Sonography, however, remains the prime imaging modality of choice.

Adrenal abscess

Adrenal abscess is a very rare condition and sometimes complicates the pre-existing adrenal hemorrhage. It is thought that hematogeneous seeding of some common bacterial infections such as E. coli and Staph. aureus occurs.

Sonographically, one cannot differentiate an abscess from a hemorrhage, but clinically the child may have evidence of infection with a fever and a high white cell count.

Adrenal cystic lesions

Cystic adrenal masses are rare, but there are some conditions in which lesions may appear cystic:

Figure 4.5 Adrenal cyst found incidentally in a well child. Prone longitudinal scan showing a well-defined cyst above the left kidney. These are very rare but are sometimes seen in Beckwith–Wiedemann syndrome. Neuroblastoma can sometimes be purely cystic. The sonographer must ensure this is not an obstructed duplex.