Bilateral adrenal lesions include a spectrum of disorders: neoplastic disorders (metastases, lymphoma, bilateral phaeochromocytoma, adrenocortical carcinoma and myelolipoma); longstanding congenital adrenal hyperplasia and macronodular adrenal hyperplasia; infections such as tuberculosis, histoplasmosis and blastomycosis; adrenal haemorrhage; adrenals in hypoperfusion complex and paediatric masses. Bilateral distribution in addition to other imaging characteristics can help narrow differential diagnoses in case of adrenal masses. We present a pictorial review highlighting the adrenal lesions that can present bilaterally.
Adrenal masses are common and found in 9% of the population. Imaging characteristics that help in differential diagnosis of adrenal lesions include size, attenuation, washout values, presence of calcification, fat or haemorrhage and unilateral versus bilateral distribution. Though the imaging differentiation of adrenal masses into benign and malignant rests to a large extent on the attenuation values of the lesion in pre-contrast study, other imaging features that help to narrow the differential diagnosis include dynamics of contrast uptake and washout characteristics and unilateral versus bilateral distribution; unilateral versus bilateral distribution also helps to narrow the differential diagnosis of adrenal masses as there are a few lesions that present bilaterally. This pictorial review shows a spectrum of bilateral adrenal lesions.
The adrenals are small, glandular organs situated in close proximity to the kidneys. Each gland is located medial to the upper pole of the associated kidney. The right adrenal gland has a linear or V shape, whereas the left adrenal gland is V- or Y-shaped. The limbs of each adrenal gland are 2–5 cm long and 6–10 mm thick.
The normal adult adrenal glands are difficult to visualise with ultrasound. However, they are almost always visualised in newborns.[3, 4] This is attributed to physiological hypertrophy at this stage of life. In adults, the right adrenal gland is regularly visible using optimised examination techniques. The left adrenal gland is visualised in about 40–50% of cases only.
The adrenals are routinely visualised on all computed tomography (CT) and magnetic resonance imaging (MRI) examinations of the abdomen.
Bilateral adrenal masses
The differential diagnosis of bilateral adrenal masses (Table 1) include neoplastic disorders – metastases, lymphoma, bilateral phaeochromocytoma, adrenocortical carcinoma, myelolipoma; longstanding congenital adrenal hyperplasia and macronodular adrenal hyperplasia; infections such as tuberculosis, histoplasmosis and blastomycosis; and adrenal haemorrhage.
Table 1. Bilateral adrenal lesions
Congenital adrenal hyperplasia
Macronodular adrenal hyperplasia
Adrenal glands are a common site of metastases from lung, breast, gastric, renal, pancreatic and colon carcinomas; melanomas and malignant lymphomas, usually non-Hodgkin's lymphomas. About 90% of adrenal metastases are carcinoma; the rest are sarcoma or melanoma. Adrenal metastases occur in 20–45% of cancer patients. They occur in less than 10% of lung cancer patients at the time of presentation. Overall, adrenal metastases are bilateral in 49% cases, occurring more commonly on the left side. However, metastases of lung cancer are mostly solitary, unilateral, small asymptomatic lesions. Bilateral metastases are observed in less than 3% of patients with lung cancer (Fig. 1a,b).
On contrast-enhanced computed tomography (CECT), the peak contrast enhancement is variable. Adrenal metastases show slow washout (absolute and relative percentage washout, absolute percentage washout (APW) and relative percentage washout (RPW) values of less than 60% and 40%, respectively) as compared with adenomas. Hypervascular metastases, in particular metastases from renal cell carcinoma and melanoma, enhance similar to phaeochromocytoma. On MRI metastases exhibit low signal intensity on T1-weighted images and high-signal intensity on T2-weighted images, with progressive enhancement on administration of contrast. There is lack of signal drop on out-of-phase images in contrast to adenomas.
Primary adrenal lymphoma is rare. More commonly, adrenals are secondarily involved. Non-Hodgkin lymphoma is the most common type with reported incidence of adrenal involvement of 4%. Bilateral involvement occurs in 50% of these cases. CECT shows discrete masses of variable attenuation or infiltrative ill-defined masses (Fig. 2a,b). Lymphoma is characterised by low-signal intensity on T1-weighted images and heterogeneous high-signal intensity on T2-weighted images, with minimal progressive enhancement.
Phaeochromocytomas are typically unilateral; bilateral lesions occur in 10% cases. Bilateral disease is more likely to occur in the setting of various syndromes including multiple endocrine neoplasia type 2, Von Hippel–Lindau disease, neurofibromatosis type 1, tuberous sclerosis and Sturge–Weber syndrome. They are significantly larger than adenomas. These functioning tumours secrete catecholamines and manifest as hypertension and palpitations. On CECT, they appear as homogenous masses (if small) or heterogeneous lesions (larger lesions) (Figs 3, 4). Pre-contrast attenuation may be similar to that of adenomas as they can contain abundant fat and show areas of cystic degeneration. Phaeochromocytoma is typically described as brightly enhancing but can show a range of CT appearances. Washout characteristics are variable, and in conjunction with marked peak enhancement, phaeochromocytomas may mimic adenoma (APW > 60%, RPW > 40%).[12, 13] The MRI appearance of a phaeochromocytoma is typically described as T2 hyperintense; however, not all phaeochromocytomas have this imaging feature (Fig. 5a,b).
Adrenal carcinoma is a rare neoplasm arising from the adrenal cortex and is bilateral in 10% cases. Almost half are functioning tumours and usually manifest with Cushing syndrome. Adrenal carcinomas are large at presentation, with size ranging from 4 to 10 cm. Heterogeneity with central necrosis is common, and calcification is noted in 30% of cases. On contrast administration, they show heterogeneous enhancement with a peripheral rim enhancement noted in some cases. They show slow washout (APW and RPW of less than 60% and 40%, respectively).
Myelolipomas are rare benign tumours composed of myeloid, erythroid and fatty elements. They are estimated to occur in 0.2–0.4% of the population based on autopsy series. The imaging appearance of myelolipomas is based on the fat content of the lesion (Fig. 6a,b). They appear echogenic at ultrasound, low attenuation at CT and hyperintense on T1-weighted in-phase MRIs. Myelolipomas may occasionally be associated with endocrine dysfunction – Cushing syndrome, Conn's syndrome, Nelson syndrome, 17-hydroxylase deficiency and 21-hydroxylase deficiency. The imaging appearance of isolated myelolipomas and those occurring in conjunction with other pathologic lesion is considerably different. Isolated lesions have an average size of 10 cm, fat content between 50% and 90%, calcification in 24% and a pseudocapsule in 75% lesions. Myelolipomas that occur in conjunction with other pathologic conditions are smaller (mean, 7 cm) with less fat (most frequently <10%), a higher frequency of calcification (52%) and lower prevalence of a pseudocapsule.
Adrenal cortical hyperplasia
Adrenal cortical hyperplasia is often seen in patients with Cushing syndrome, which is the result of hyperproduction of adrenocorticotropic hormone. It may be diffuse or nodular and is typically bilateral. Diffuse cortical hyperplasia is seen in 45% of patients with Cushing syndrome, whereas nodular cortical hyperplasia is seen in only 3% of these patients. The signal intensity of hyperplastic adrenal glands is usually similar to that of the normal adrenal gland.
Congenital adrenal hyperplasia (CAH)
CAH refers to a group of inherited disorders of adrenal steroidogenesis. The common functional defect is impaired cortisol secretion, resulting in hypersecretion of corticotropin-releasing hormone and adrenocorticotropic hormone and consequent hyperplasia of the adrenal glands. About 90% cases of CAH are caused by a defect in the enzyme 21-hydroxylase. Clinically, patients with CAH can present as classic salt-losing (most severe), classic non-salt-losing (simple-virilising) or non-classic (mild or late-onset) form. In untreated cases, a variety of morphologic changes can occur in adrenals including symmetrical enlargement, macronodules and rarely adenoma and carcinoma (Fig. 7a–c).
Tuberculosis, histoplasmosis and blastomycosis can affect the adrenals. These infections result in bilateral enlargement of the adrenals (Fig. 8a). With long-standing infection, the glands may atrophy and calcify. Extensive involvement of the adrenals by these infections may result in adrenal insufficiency (Fig. 8b). In fact, tuberculosis is the most common cause of Addison disease worldwide.
Trauma accounts for 80% cases of adrenal haemorrhage (Fig. 9a). Other causes include systemic anticoagulation therapy, sepsis or stress such as surgery. Bilateral haemorrhage occurs in 20% cases. Adrenal haemorrhage is an unusual cause of adrenal insufficiency. Acute adrenal haemorrhage is hyperdense at CT. Chronic adrenal haemorrhage has typical MRI appearance with hyperintensity on T1-weighted images and a dark rim along the periphery on T2-weighted images.
Neonatal adrenal haemorrhage is a relatively uncommon clinical problem. It is noted in approximately 3% of infants screened by ultrasonography (Fig. 9b). The aetiology of adrenal haemorrhage is unclear. Associations include traumatic delivery, hypoxia, shock, septicaemia and bleeding diathesis.
Other masses that can present bilaterally include adrenal cysts of varying aetiology, adenomas and Rosai–Dorfmann disease (Fig. 10).
Paediatric adrenal bilateral neoplasms
Bilateral lesions are rare in neuroblastoma and occur in less than 10% cases. Bilateral adrenal neuroblastoma have been described in up to 20% of patients with familial neuroblastoma. Most of the patients with bilateral neuroblastomas are less than 6 months of age. The incidence of Stage 4S is higher in bilateral neuroblastoma than among unilateral tumours. At ultrasonography, neuroblastoma appears as a hetero-echoic mass. At CT, neuroblastoma appears as either a homogeneous or heterogeneous soft tissue mass. Heterogeneity is caused by haemorrhage, necrosis and/or calcification. Coarse, finely stippled or curvilinear calcifications are seen in 85% of the abdominal neuroblastomas.
These tumours have a less malignant potential as compared with neuroblastoma. Therefore, they tend to be smaller and well defined at presentation. They demonstrate intermediate signal intensity on T1-weighted images and heterogeneously high-signal intensity on T2-weighted images. They enhance heterogeneously following contrast administration.
Bilateral adrenal lesions other than masses
Adrenals in hypoperfusion complex
Although not enlarged, an interesting bilateral appearance of adrenals is noted in hypoperfusion states. Adrenals show bilaterally symmetrical intense enhancement with attenuation values similar to or greater than those of inferior vena cava (IVC) (Fig. 11a). This along with flat IVC gives a clue to the diagnosis (Fig. 11b). It represents a sympathetic response to shock and preservation of perfusion to adrenals that are vital organs.
Autoimmune Addison disease
Adrenal insufficiency of autoimmune origin is the most common cause of Addison disease in developed countries. On imaging, both the adrenals are markedly atrophic (Fig. 12a,b).
Bilateral adrenal lesions when encountered are often explained in the context of clinical picture and primary disorders such as metastases, lymphoma, hyperplasia, haemorrhage and myelolipoma have fairly characteristic imaging appearances.
Some lesions may be difficult to differentiate such as adrenal carcinoma versus neuroblastoma versus lymphoma in children. Although accompanying liver lesions may be seen in all three, splenic lesions and lymphadenopathy favour lymphoma over adrenal carcinoma and neuroblastoma (Table 2).
Table 2. Approach to bilateral adrenal masses. CAH, congenital adrenal hyperplasia; NCCT H.U., non-contrast computed tomography, Hounsefield Unit