Congenital adrenal hyperplasia (CAH) is collection of autosomal recessive disorders characterized by low cortisol production, potential aldosterone deficiency, and androgen excess due to an enzymatic defect in the cholesterol-steroid biosynthesis pathway [5]. Over 95 % of cases are due to a deficiency in the enzyme 21-hydroxylase [5]. Androgen excess leads to virilized genitalia in female infants and early virilization in male infants [11]. In the most severe form, concomitant aldosterone deficiency leads a salt-losing crisis in either sex during the newborn period [5]. Diagnosis can be made by a very high concentration of 17-hydroxyprogesterone (17-OHP) after three days of life [16].

Most neonates with CAH have enlargement of the adrenal glands with a width measurement of >4 mm and a length measurement of >20 mm [17]. Additional signs which may be seen on US include a cerebriform appearance of the surface of the adrenal gland and a stippled central adrenal echogenicity [18, 19]. In a series by Al-Alwan et al., US in the immediate neonatal period had a sensitivity of 92 % and a specificity of 100 % for the diagnosis of CAH and may be employed before conclusive 17-OHP levels are available [18]. Diagnosis of CAH can be made by the demonstration of two of three sonographic signs: (1) adrenal limb width of >4 mm, (2) cerebriform or crenated appearance of the surface of the adrenal gland, and (3) replacement of the central hyperechoic stripe with a diffusely stippled pattern of echogenicity or a diffuse thickened band of echogenicity (Fig. 16.5) [18].

Case reports suggest that CAH due to deficiencies in 11β-hydroxylase or 3β-hydroxysteroid dehydrogenase leads to similar changes on adrenal US [20]. Lipoid adrenal hyperplasia is a rare form of CAH due to cholesterol desmolase deficiency, and adrenal glands appear enlarged with echogenicity or attenuation similar to fat due to accumulation of cholesterol and its esters [21].

When adrenocortical hyperplasia presents in older children, it is classified as primary or secondary [1]. Primary adrenocortical hyperplasia results in either Cushing syndrome or, less commonly, primary hyperaldosteronism (Conn syndrome) [1]. Secondary adrenocortical hyperplasia is due to excess ACTH: either endogenous in those with Cushing disease or ectopic ACTH production or exogenous in those receiving ACTH administration (e.g., for infantile spasms) [1]. Clinical features of Cushing syndrome include central obesity, moon facies, buffalo hump, proximal muscle weakness, easy bruisability, abdominal striae, hypertension, dyslipidemia, insulin resistance, and elevated 24-h urinary cortisol and 17-hydroxycorticoids [22]. Clinical manifestations of Conn syndrome include muscle weakness, hypokalemia, and hypertension [23].

Adrenal glands are not normally visible by US in older children; therefore, if they are visible, the diagnosis of adrenal hyperplasia should be entertained [1]. CT and MR may be used to visualize the adrenals in older children with adrenal hyperplasia. Hyperplastic adrenal glands in these cases will be bilaterally, symmetrically, and evenly enlarged with increased relative enhancement [1]. Alternatively, in some cases of adrenal hyperplasia, adrenal glands may be normal in size, demonstrate uneven enlargement, or contain small nodular areas (Fig. 16.6) [1].

Cushing syndrome and Conn syndrome can also be associated with adrenal adenomas. Benign adrenal adenomas cannot be reliably distinguished from adrenal carcinomas based on histopathology, clinical features, or imaging [24]. However, in general, adrenal adenomas are smaller (<6 cm) compared to adrenal carcinoma and have less heterogeneity on US, CT, and MR. Adrenal carcinomas can have a similar appearance to adrenal adenomas, but tend to be larger and more complex [24]. The only definitive signs of malignancy are hematogenous metastases or venous spread [24].

Primary pigmented nodular adrenocortical disease is a rare form of Cushing syndrome and is associated with Carney complex (Sertoli cell tumors of the testis, cardiac myxomas, soft tissue myxomas, and skin pigmentation) [25]. On imaging, the adrenal gland has multiple, <2 mm cortical-secreting adenomas with atrophic cortex between the nodules [25].

Wolman disease, a rare disorder, is an inherited deficiency of lysosomal acid lipase leading to the accumulation of cholesterol esters and triglycerides in many organs, especially in the adrenals [3]. Wolman disease presents in the first few weeks of life with hepatosplenomegaly with abdominal distension, jaundice, vomiting, diarrhea, steatorrhea, anemia, and growth failure and is rapidly progressive leading to death in the first year [3, 5]. On US, the adrenals appear markedly enlarged with calcifications appearing as a long, linear echogenic band with posterior acoustic shadowing [5]. On CT, the adrenals also appear enlarged with a cortical distribution of calcification [5]. Plain film will also demonstrate the densely calcified adrenal gland (Fig. 16.7) [5]. Imaging of adrenals in Wolman disease can look similar to resolving adrenal hemorrhage; however, in adrenal hemorrhage the adrenals are smaller and have globular calcifications [5, 26, 27].

Adrenal hemorrhage in the perinatal period can occur in response to perinatal stress (such as difficult or traumatic delivery, hypoxia, or sepsis) or bleeding disorders [29]. Large babies such as those of diabetic mothers or with Beckwith-Wiedemann syndrome have a higher predisposition [30]. Associated clinical signs may include palpable flank mass, anemia, jaundice, or rarely hypovolemic shock. However, there is normally no associated adrenal insufficiency in the immediate phase or long-term as the major insult is to the regressing fetal cortex [5]. Beyond the neonatal period, adrenal hemorrhage is frequently seen in the setting of trauma but has also been documented to occur in older children with overwhelming sepsis (specifically Neisseria meningitidis), steroid therapy, anticoagulation therapy, and after liver transplantation [5, 11].

Adrenal hemorrhage more often occurs on the right (70 %), and in only 10 % of cases does it occur bilaterally [5]. Hemorrhage size can vary from as small as a few centimeters and up to several centimeters [5]. With conservative management, the natural course of adrenal hemorrhage is central liquefaction with resorption of blood leading to eventual decrease in size to the normal shape and a residual focus of calcification [5].

US is the modality of choice for initial imaging of adrenal masses in neonates as well as for follow-up assessment [31, 32]. On initial US, adrenal hemorrhages have a varied appearance depending on the duration of the hemorrhage. They usually have complex echogenicity with echogenic and echo-free areas but can also appear evenly echogenic, hypoechoic, or anechoic [5]. Smaller hemorrhages may be focal or retain the shape of the adrenal (triangular or crescent-shaped), and adjacent normal adrenal tissue can be identified. Larger adrenal hemorrhages are usually round in shape, and normal unaffected adrenal tissue can be hard to identify (Figs. 16.8a, b) [5]. Large hemorrhages may encompass the upper pole of the kidney (with the appearance of a perinephric hemorrhage) and may track down the retroperitoneum. Clinically, this can lead to scrotal swelling and hematoma, which may mimic testicular torsion [5, 33]. Occasionally, there may be associated ipsilateral renal vein thrombosis, especially on the left since the adrenal vein drains into the left renal vein [5]. To help differentiate adrenal hemorrhage (which is avascular) from neuroblastoma or other adrenal neoplasms, evaluation with color and spectral Doppler assessment should be performed (Fig. 16.8c). Additionally, ultrasound examination should include evaluation of the liver to assess for the presence of hepatic metastases and evaluation of the remainder of the abdomen and pelvis to look for metastatic lymphadenopathy, which can be seen in association with adrenal tumors.

Because of the varied imaging characteristics of adrenal hemorrhage in the acute phase, it may be difficult initially to distinguish from neuroblastoma [34, 35]. Thus, follow-up US imaging is of utmost importance in differentiating a resolving adrenal hemorrhage from a neuroblastoma. Masses due to adrenal hemorrhage decrease in size over several weeks as the hemorrhage liquefies and resorbs and become more hypoechoic or anechoic (Fig. 16.9) [36], whereas in contrast, the size of a neuroblastoma is unlikely to decrease. In cases where the diagnosis is uncertain, a short delay with serial US imaging is not harmful as neonatal neuroblastoma has a relatively good prognosis [11].

In some instances adrenal calcification may be incidentally seen on imaging (plain film, CT, MR) on older children. If the calcification is confined to adrenals of normal size and without evidence for a soft tissue mass, it is assumed to have resulted from previous adrenal hemorrhage in the neonatal period and is of no clinical significance (Fig. 16.10) [5].

In neonates with a suprarenal retroperitoneal mass, the possibility of an intra-abdominal extralobar pulmonary sequestration must also be considered in addition to adrenal hemorrhage and neuroblastoma [3]. Intra-abdominal extralobar pulmonary sequestrations occur more commonly on the left than the right, are usually hyperechoic, and can contain cysts related to coexistent congenital pulmonary airway malformation (Fig. 16.11) [28, 37]. As imaging with US, CT, and MR is rarely diagnostic, surgical diagnosis and treatment is often necessary [38].

Medullary adrenal neoplasms include the neuroblastoma, ganglioneuroblastoma, ganglioneuroma, and pheochromocytoma. These can occur within the medulla of the adrenal gland but also along the sympathetic nervous chain [1].