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ADRENAL GLANDS
Normal appearances
In utero and postnatally, the adrenal glands are large, about one-third the size of the kidney, and composed mainly of the bulky, hypoechoic fetal cortex which makes up about 80% of the gland. The neonatal adrenal glands are easily demonstrated on ultrasound. The bulky fetal cortex is sonographically apparent as a thick hypoechoic layer surrounding the thinner, hyperechoic adrenal medulla. The fetal cortex surrounds the smaller, permanent cortex and gradually starts to involute after birth. By the age of 2–4 months, the adrenal glands have attained their normal adult configuration of the thin, hypoechoic cortex with a tiny layer of hyperechoic adrenal medulla within.
Neuroblastoma
The neuroblastoma is a malignant tumour arising in the sympathetic chain, most commonly the adrenal medulla. The majority of neuroblastomas present before the age of 4 years with a palpable abdominal mass, and many already have metastases at the time of presentation to the liver, bone marrow, skin or lymph nodes.
The tumour is usually large on presentation, displacing the kidney downwards and laterally. In some cases it may invade the adjacent kidney, becoming difficult to distinguish from a Wilms’ tumour. Neuroblastoma is predominantly solid on ultrasound, having a heterogeneous texture and frequently containing calcification.
The tumour margins are ill-defined and infiltrate the surrounding organs and tissues, crossing the midline and encasing vascular structures: it may be difficult to differentiate from lymphadenopathy. Nodes tend to surround and elevate theaorta and IVC. MRI and CT are used for staging, particularly in assessing retroperitoneal spread. Bone scintigraphy and MIBG scans are also useful in demonstrating metastases.
Adrenal haemorrhage
After birth, the bulky fetal cortex normally involutes. Adrenal haemorrhage occurs in the neonate as a result of trauma to the vulnerable fetal cortex during delivery or in association with perinatal asphyxia. Haemorrhage may occur in up to 2% ofbirths. This may be uni- or bilateral and may cause a palpable mass and abdominal pain. Ultrasound can be used to follow the resolution of the haemorrhage over a period of weeks; in the initial stages of haemorrhage the adrenal mass is hyperechoic, gradually liquefying into a welldefined mass of mixed echo pattern and becoming cystic. This may completely resolve over a period of some weeks leaving a normal adrenal gland or the gland may become atrophic and calcify. In rare cases an adrenal haemorrhage may progress to an abscess.
Adrenal calcification
Calcification of the gland in babies and infants is usually the result of previous infection or haemorrhage. Adrenal abscess cavities may calcify after successful treatment. Gross calcification in bilateral adrenal glands in association with hepatosplenomegaly in the infant indicates the likely diagnosis of Wolman’s disease, an inborn error of lipid metabolism that is invariably fatal.
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