Adrenal Lesion (Incidental)

• Adrenal lesions may be seen on imaging in patients with symptoms due to functioning adrenal lesions, or in patients with adrenal metastases due to extra-adrenal malignancy. However, the majority are encountered as incidental adrenal lesions (IALs).
• An adrenal 'incidentaloma' is defined as:
  • “An adrenal mass detected on imaging not performed for a suspected adrenal disease” (European Society of Endocrinology) 1 or
  • “An incidentally detected adrenal nodule or mass that is unrelated to the clinical indication for the imaging examination performed”. (Society of Abdominal Radiology) 2
  • Some authorities (e.g. Canadian Urological Association, 2023, ACR , 2017, Society of Abdominal Radiology, 2023)(2-5) limit the definition of IALs to adrenal masses greater than 10mm in size., as does a recent article by Seow et al 6. The ACR goes further stating that a IAL < 1 cm in the short axis need not be pursued 5
• The Society of Abdominal Radiology (SAR, 2023) 2 determined by expert consensus that a distinction should be made between adrenal nodules (<4cm in size) and adrenal masses (>4cm), the rationale being that malignancy becomes much more common in lesions >4cm 2, 7, 8
• The SAR has also sought to establish a standard lexicon for use in reporting adrenal abnormalities 2
• IALS may be 4:
  1. Benign lesions:
     1. Features suggestive of benignity include:
        • Unenhanced CT attenuation of <10 HU (highly specific)- but see Click here for important note
        • Absolute percentage washout greater than 60% or relative percentage washout greater than 40% on Adrenal Washout protocol CT) - but see Click here for important note
        • On Chemical Shift MR scan, loss of signal intensity on out-of-phase T1 weighted MR images, compared to in-phase signal intensity
     2. Benign, non-functioning adenomas:
        • By far the most common IAL (up to 75%)
        • Other much less common benign IALs include myelolipomas, cysts, lymphangiomas, and ganglioneuromas.
     3. Benign, hyperfunctioning lesions:
        • Include cortisol-secreting adenomas (5.3% of IALs), aldosterone-secreting adenomas (1%) or catecholamine-secreting phaeochromocytomas (5%)
  2. Malignant lesions.
     • Include adrenocortical carcinoma (ACC), metastases, and malignant phaeochromocytoma (PCC)
     • Features suggestive of malignancy include heterogeneity, necrosis, or irregular margins, or if it can be shown to have enlarged
• The definition should exclude:
  • Patients with symptomatic lesions (i.e. symptoms either due to local effects or hormonal secretion),
  • Patients with asymptomatic adrenal lesions who are undergoing imaging for staging or follow-up of known or previous malignancies that may be expected to metastasise to the adrenals, and
  • Patients with clinically suspected adrenal disease 6.
• Adrenal nodules occur in 5-7% of the population 9 and incidental adrenal masses are found in up to 4-5% of CT and MRI scans 10-13 reaching 10% or more in elderly patients (i.e. the prevalence increases with age) 14
• The relevant questions that require answering when investigating an incidental adrenal nodule
  • Is the lesion benign or malignant? If it is likely to be malignant, is it a metastasis or an adrenal carcinoma?
  • Is it a phaeochromocytoma
  • If it is an adenoma, is it functioning / secreting?
• In patients with no known primary malignancy, the likelihood of an adrenal nodule being malignant is less than 0.5%, whereas in a patient with a known malignancy, the prevalence is 25-36% 15. 
• Even in a patient with known malignancy , unless there are other metastases, the majority of adrenal lesions will be benign 16.
  • However, considering adrenal lesions overall, in patients with adrenal lesions and a past history of extra-adrenal malignancy, the majority of these adrenal lesions are benign ; and even in those patients with current extra-adrenal malignancy (but without other extra-adrenal metastatic disease), 50% of adrenal lesions are benign- 16
  • In patients with adrenal lesions , extra-adrenal malignancy and extra-adrenal metastases, 25% of the adrenal lesions are benign. 16
• The prevalence of the different causes of incidental lesions varies widely in the literature. In a review published in 2008, adenomas constituted 75% of all IALs, myelolipomas 6%, hematomas 4%, cysts 1%, phaeochromocytomas 0.3%, and cortisol-producing adenoma 0.1% were found incidentally. In 973 consecutive patients with an incidental adrenal mass and no history of cancer, no malignant lesions were identified 10. 
• Myelolipomas, haematomas and cysts can usually be accurately diagnosed on their specific imaging appearance
• Further investigation of an incidentally found adrenal mass will depend on clinical suspicion based on patient characteristics and clinical background and will consist of clinical, biochemical, and radiological evaluation to establish the lesion’s secretory status and risk of malignancy
• Imaging phenotype and mass size are the two major predictors of malignancy in incidental adrenal lesions  
• The most common malignant adrenal lesion is a metastasis. Primary adrenal adenocarcinomas are rare. Traditionally it is considered that 10% of phaeochromocytomas are malignant 15, 17
• A study of patients with no known malignancy and no suspicion for a hyperfunctioning adrenal mass found that imaging provided a specific diagnosis in 87% of all adrenal masses, of which 62% were diagnostic on the original CT 10.
• The large majority of incidentally discovered adrenal adenomas are non-functioning. Of those that are functioning, increased cortisol production is the most common abnormality, causing ‘sub-clinical’ Cushing’s syndrome (Mild Autonomous Cortisol Secretion (MACS) Clinical and biochemical work-up or ‘metabolic syndrome’ (increased frequency of hypertension, central obesity, impaired glucose tolerance or diabetes, hyperlipemia and osteoporosis)18. These patients have an increased risk of cardiovascular events and mortality 19, 20. Other functioning lesions may secrete mineralocorticoids or catecholamines ( i.e. phaeochromocytoma) 21
• Patients with bilateral adrenal incidentalomas are considerably more likely to have functioning adenomas, especially hypercortisolism (22% versus 6% for those with unilateral adenomas) 22

• Clinical history and physical examination should be aimed at eliciting evidence of adrenal hormone excess (e.g. Cushing’s Syndrome, hyperaldosteronism, phaeochromocytoma, hypertension, virilisation, feminisation, or history suggestive of extra-adrenal malignancy predisposing to adrenal metastases, including smoking history)
• Consideration should be given to referral to an endocrinologist if there is suspicion of the above
• Biochemical confirmation is beyond the scope of this article
• In a report of IALs from a tertiary centre, autonomous cortisol secretion was present or suspected in 6.6%, phaeochromocytoma in 4.7%, hyperandrogenism in 3.1%, and primary hyperaldosteronism in 2.4% of patients 23

• If a functioning lesion is present, management will be dependent on the type of lesion present and the clinical context and will range from monitoring to medical therapy to surgery (open or minimally invasive)

Which patients should undergo biochemical assessment?

The detailed description of biochemical tests is beyond the scope of this article. Readers are referred to the 2023 European Society of Endocrinology guidelines 1 for details. 

However, it should be noted that:

• Patients with bilateral adrenal incidentalomas are considerably more likely to have functioning adenomas, especially hypercortisolism - 22%, versus 6% for those with unilateral adenomas 22
• Two-thirds of all ACCs are hormonally active and tend to manifest with hypercortisolism and virilization (and, rarely, aldosteronism and feminization). In general, however, the ACCs manifesting as radiographic incidentalomas are clinically nonfunctioning tumours 24, but such lesions are very rare.
• All major guidelines recommend clinical assessment for evidence of hormonal excess
• Biochemical assessment should be for evidence of Cushing’s syndrome or subclinical Cushing’s Syndrome
• In patients with hypertension and/or hypokalaemia, biochemical assessment of the aldosterone/renin ratio is advised to detect primary hyperaldosteronism
• Patients (especially those with hypertension) with lipid-poor (>10HU), enhancing masses (particularly >4cm) should have plasma free or urinary fractionated metanephrines measured to exclude phaeochromocytoma

Major guideline recommendations

• The European Society of Endocrinology guidelines state: 1 
  • Every patient needs a thorough clinical and endocrine work-up to exclude hormone excess including the measurement of plasma or urinary metanephrines and a 1-mg overnight dexamethasone suppression test (applying a cutoff value of serum cortisol ≤50 nmol/L [≤1.8 µg/dL]). The latter test may not be necessary in frail or elderly patients with limited life expectancy 25.
• The Canadian Urological Association also recommends 4 that:
  • All patients should be assessed biochemically
• The ACR and the American Association of Clinical Endocrinologists and the American Association of Endocrine Surgeons recommend biochemical screening of most if not all patients 9, 26, 27.
  • The AACE recommends investigation for subclinical Cushing’s Syndrome, for primary hyperaldosteronism in patients with hypertension and/or hypokalaemia, and for phaeochromocytoma in all lipid poor masses 27. 
  • Patients with a homogeneous, and lipid-rich adrenal mass (<10 HU) that is not hypervascular on post-contrast CT do not require biochemical evaluation for phaeochromocytoma 27
• Seow et al 6 and Corwin et al 28 recommend that:
  • Radiology reports should include a recommendation to perform a hormonal evaluation for all IALs, excluding obvious myelolipomas and cysts; this will lead to the identification of nearly all PCCs, as well as most ACCs

If a functioning lesion is present, management will be dependent on the type of lesion present and the clinical context and will range from monitoring to medical therapy to surgery (open or minimally invasive).

Mild Autonomous Cortisol Secretion (MACS)

• Additionally, endocrine correlation identifies sub-clinically functional adenomas (including MACS) 1, 6, where clinical management may take precedence. Recommending additional endocrinologist referral may depend on local preferences, as in some regions, to manage cost and access issues, endocrine testing can be performed by primary care physicians, with endocrinologist referral limited to those with abnormal results.
• Recent studies have provided evidence that most patients without clinical signs of overt Cushing’s syndrome but serum cortisol levels post-dexamethasone >50 nmol/L (>1.8 µg/dL) harbour increased risk of morbidity and mortality. For this condition, the term “mild autonomous cortisol secretion” (MACS) is proposed (1)
• All patients with MACS should be screened for potential cortisol-related co-morbidities that are potentially attributable to cortisol (e.g., hypertension and type 2 diabetes mellitus), to ensure these are appropriately treated 1
• The European guidelines also recommend screening patients with MACS for asymptomatic vertebral fractures 1
• A systematic review summarised by the Canadian Urology Association 4, but based on predominantly observational studies reported that subclinical Cushing’s syndrome/MACS is associated with type 2 diabetes, hypertension, cardiovascular events, vertebral fractures, and mortality. However, on follow-up, no patients developed overt Cushing’s syndrome. The conclusion was that MACS, while having a low risk of progression to Overt Cushing’s syndrome, can still contribute to morbidity.
• In patients with MACS who also have relevant comorbidities surgical treatment should be considered in an individualized approach (1). Age, sex, general health, degree and persistence of non-suppressible cortisol after dexamethasone, severity of co-morbidities, and patient’s preferences should be taken into account. In all cases, the proposal to perform surgery should be discussed within an expert multidisciplinary group.

• There are differing opinions regarding follow-up of benign non-functioning adenomas 29, 30 
• Follow-up is directed at showing increase in size of the lesion (which may indicate malignancy) and / or the development of hormonal activity
• However, most of the recently published guidelines do not recommend follow-up imaging or follow-up biochemical testing for benign non-functioning incidental adenomas <4cm in size 1, 4, 9
• The ESE guidelines (2023) recommend against repeated hormonal work-up in patients with hormonal work-up results within the reference range at initial evaluation unless new clinical signs of endocrine activity appear or there is worsening of relevant comorbidities (eg, hypertension, type 2 diabetes) 1

• The 2009 AACE/AAES guidelines recommend follow-up imaging at 3-6months and then annually for 1-2 years 24, although this is usually regarded as outdated
• A 2009 article compared the cost-effectiveness of various follow-up strategies for benign IALs <4 cm and determined that, above a prevalence of 0.7% , the most optimal, cost-effective strategy is a one-time follow-up evaluation involving non-contrast CT and biochemistry31
• If an adrenal mass has diagnostic features of a benign mass such as a myelolipoma (presence of macroscopic fat), cyst, or haemorrhage (masses without enhancement, defined as change in pre- and postcontrast imaging of <10 HU), no additional workup or follow-up imaging is needed. Similarly, a benign calcified mass, such as an old hematoma or a calcification from prior granulomatous infection, also needs no further imaging 5

Background evidence

• In large studies of patients who had initial characteristic radiological features of a benign adenoma, almost no patients were found to develop an adrenal malignancy 4, 7, 10, 32
• Older studies suggest that the likelihood of developing hormonal dysfunction is probably increased in the first 3-5 years of follow-up and then tends to plateau 33, 34, with masses >3cm and / or with subclinical Cushing’s syndrome at baseline more likely to develop overt hormonal dysfunction over time

• However, the risk of developing clinically relevant hormonal excess when the initial workup demonstrates a non-functioning lesion is low 30.  Studies with a total of more than 3000 patients with nonfunctioning adrenal incidentaloma confirm that the risk of developing clinically relevant overt hormonal excess is extremely low: 0.0%-0.6% for Cushing’s syndrome, 0.0%-1.6% for primary aldosteronism, and 0.0%-2.1% for phaeochromocytoma 1.
• A recent large retrospective study of IALs detected on post-contrast CT scans found the prevalence of malignancy in patients without known cancer to be exceedingly low. The authors suggest that follow-up imaging is not warranted for small 1-2(1-2 cm) incidental indeterminate adrenal nodules detected on contrast-enhanced CT in patients without known cancer 35.
• An approach individualized to the patient would appear to be reasonable, based on patient’s age, co-morbidity and the confidence of the lesion being benign on initial imaging

• Traditionally, lesions >4cm discovered incidentally (with no evidence of extra-adrenal malignancy)  have undergone resection, based on the data from old studies 36, 37 that found that most ACCs and PCCs are >4cm on diagnosis
• However, there is little follow-up data of benign-appearing, large adrenal incidentalomas to support this
• Phaeochromocytoma should be excluded clinically and biochemically
• Rowe et al (Canadian Urological Association) has a weak recommendation that follow-up imaging at 6-12 months of benign appearing, non-functioning masses >4cm should be considered 4
• The 2023 European guidelines state that only lesions >4 cm that are inhomogeneous or have HU >20 have sufficiently high risk of malignancy that surgery will be the usual management of choice 1
• However, the 2021 ACR Appropriateness Criteria recommend that incidental lesions >4cm that do not have diagnostic benign features should have no further imaging , but should undergo surgical resection (without biopsy)due to the risk of Adrenal Cortical Carcinoma 38

• Available evidence suggests that in patients with a history of an extra-adrenal malignancy, only 7% of adrenal metastases have an attenuation of <10 HU on CT
• Lesions >10 HU, however, are malignant in 70% of patients with a history of extra-adrenal malignancy 4, 39
• However, considering adrenal lesions overall, in patients with adrenal lesions and a past history of extra-adrenal malignancy, the majority of these adrenal lesions are benign (especially those <20HU); and even in those patients with current extra-adrenal malignancy (but without other extra-adrenal metastatic disease), 50% of adrenal lesions are benign 16
• In patients with adrenal lesions , extra-adrenal malignancy and extra-adrenal metastases, 25% of the adrenal lesions are benign 16

• When characterization of these lesions will alter clinical management, adrenal biopsy and/or fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG-PET) can be useful adjuncts 1, 4, 40, 41

• While PET/CT has good diagnostic accuracy for identifying malignancy of adrenal tumours, there is limited data regarding incidental adrenal lesions (IALs) 42
• Non-malignant adrenal pathology (for example inflammatory lesions) can demonstrate increased uptake on 18F-FDG-PET/CT
• Advances in imaging characterization with CT, MRI, and PET/CT have decreased the need for image-guided percutaneous biopsies to characterize adrenal masses 5
• In oncology patients, an enlarging adrenal mass, an indeterminate adrenal mass on adrenal CT, and an adrenal mass >4 cm should proceed with PET/CT or biopsy because the presumed diagnosis is metastatic disease

• 18FDG-PET/CT SCAN is useful for:
  • In studies including a mixture of patient groups, it has been shown to differentiate benign from malignant with sensitivity (73–100%) and specificity (67–100%) 1, 43-47. However , the data regarding incidental adrenal lesions is limited.
  • Excluding or confirming malignancy of adrenal lesions in high-risk populations (i.e. known or suspected extra-adrenal malignancy) (48). When characterization of adrenal lesions will alter clinical management, adrenal biopsy and 18F-FDG-PET can be useful adjuncts 1, 4
  • Detecting an occult primary malignancy when adrenal metastases are suspected
  • Detecting other extra-adrenal metastases which may affect management of the adrenal lesion
• It should be noted that a small proportion of benign adrenal cortical adenomas may show FDG uptake greater than liver background, often but not always in secretory masses. Similarly, benign phaeochromocytomas will also show increased FDG uptake 46, 49

• Considering adrenal lesions overall, in patients with adrenal lesions and a past history of extra-adrenal malignancy, the majority of these adrenal lesions are benign (especially those <20HU); and even in those patients with current extra-adrenal malignancy (but without other extra-adrenal metastatic disease), 50% of adrenal lesions are benign 16
• In patients with adrenal lesions , extra-adrenal malignancy and extra-adrenal metastases, 25% of the adrenal lesions are benign 16

• When characterization of these lesions will alter clinical management, adrenal biopsy and/or fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG-PET ) can be useful adjuncts 1, 4, 40, 41
• Three criteria should be fulfilled prior to considering adrenal biopsy 1:
  •  The lesion is hormonally inactive (in particular, a phaeochromocytoma has been excluded, since a hypertensive crisis may be precipitated by biopsy in patients with this condition),
  •  the lesion has not been conclusively characterized as benign by imaging, and
  •  clinical management of the patient would be altered by knowledge of the histology.
• The ESE recommends against the use of an adrenal biopsy in the diagnostic work-up of patients with adrenal masses unless there is a history of extra-adrenal malignancy 1

• Adrenal mass biopsy should not be performed routinely for the work-up of an adrenal incidentaloma 1, 4 unless there is a history of extra-adrenal malignancy 1
• Biopsy should be considered when the diagnosis of metastatic disease from an extra-adrenal malignancy would be of value 4 
• While biopsy can differentiate metastasis from lipid-poor adenomas and phaeochromocytomas, it cannot differentiate an adenoma from an ACC 4
• Biopsy of a suspected ACC should not be routinely performed due to potential risk of tumour seeding the needle tract 50. It runs the risk of tumour dissemination, precluding an R0 resection.
• Biopsy of ACC has been reported to lead to worse overall survival in patients with stages 1 and 2 adrenocortical carcinomas.1

• The mean complication rate of adrenal biopsy is 1.7%-2.5% 1, 4, 39. Potential complications include pneumothorax, bleeding, tumour tracking, infection, adrenal abscess formation.

• Tissue sampling  can be performed either by CT-guided biopsy or endoscopic ultrasound-guided FNA with similar sensitivities of 88.5% and 89-100%  and specificities of 91.5% and 97-100%, respectively 1

• Prior to biopsy, it is essential to ensure that a phaeochromocytoma has been excluded 4. A hypertensive crisis may be precipitated by biopsy in patients with this condition.

Recently, Seow and colleagues 6 have made a convincing argument in favour of:

• Increasing the upper CT attenuation threshold to 20 Hounsfield units for incidental nonfunctional lesions <4cm in size to replace the traditionally accepted 10HU threshold in excluding malignancy. This is supported by Bancos et al 51.
• Cessation of the use of Adrenal Washout CT (AWCT) as part of the workup of incidental adrenal masses
• Continuing to perform a biochemical workup in the majority of adrenal lesions
• Defining Incidentalomas of the adrenals to exclude lesions occurring in patients with current or prior extra-adrenal malignancy or those with clinically suspected adrenal disease

These authors’ rationale for the above is as follows:

• AWCT has largely been validated in artificially enriched (for non-benign lesions) populations
• AWCT is insufficiently reliable and diagnosis utility is limited given the extremely low prevalence of malignancy in true incidentaloma populations
• Washout CT has limited utility in evaluating incidental adrenal nodules in patients without known malignancy 8, 52, 53
• Phaeochromocytomas 54, 55 and other hypervascular lesions (such as renal cell and hepatocellular carcinoma metastases) can give results on AWCT mimicking benign lesions
• Adrenal-protocol CT overall (unenhanced attenuation ≤ 10 HU or absolute washout of ≥60%) has poor diagnostic performance when the adrenal nodule is heterogeneous 56
• The 10 HU threshold is questioned due to the reported sensitivities and specificities of a 20HU threshold of diagnosing malignancy of 96.8% and 76.7% , respectively (versus 100% and 57.5%, respectively, for 10 HU) 1
• The PPV of <20 HU for benignity has been reported as 96.2% - 99.4% 53, 57
• PPV for benignity approaches or is equal to 100% when this is combined with a 4 cm cut-off (summarised evidence by SEOW and colleagues 6
• Even in adrenal lesions >20 HU but <4 cm or <20 HU but >4 cm, malignancy rates among incidental adrenal lesions are very low

• These are benign neoplasms consisting of mature adipose and myeloid tissues
• They are the second most common adrenal incidentalomas after adenomas (7-15%) 4
• However, in a large study from a tertiary centre the prevalence was 0.24% 58
• While the majority are discovered incidentally, larger tumours may present with mass effect, retroperitoneal haemorrhage, or spontaneous rupture requiring surgical intervention. These complications are exceedingly rare events occurring more commonly in tumours measuring >6 cm 59, 60
• Adrenal myelolipomas grow in an indolent manner and remain asymptomatic in the majority of cases 61

Imaging features of myelolipomas

• Size can range from a few millimetres to greater than 10 cm.
• Macroscopic fat may be identified on CT or MRI
• When a nodule contains greater than 50% macroscopic fat, that is diagnostic of a myelolipoma 59, 62
• Some myelolipomas display calcification or areas of haemorrhage 62
• Myelolipoma, fluid-filled homogenous cysts, and other soft tissue tumours

  (ganglioneuromas, some schwannomas) have low CT density ≤10 HU. Suspected macroscopic fat measures <-10 to -15 HU

• Adrenal masses with small amounts of macroscopic fat can be benign adrenal cortical adenomas with myelolipomatous degeneration 63
• There are few reports of macroscopic fat in ACC detected on imaging studies; tumours were large (> 6 cm) and had a small proportion of gross fat (< 5%) 4

Management

• Some authors recommend intervention for large asymptomatic myelolipomas 64, 65, but there is evidence that the surveillance of adrenal myelolipomas, even in patients with lesions > 4 cm, is a safe clinical strategy, provided the imaging characteristics are benign and the patient remains asymptomatic 61
• Typical Myelolipomas <4cm do not need further work-up imaging 4
• Adrenal masses with small amounts of macroscopic fat can be benign adrenal cortical adenomas with myelolipomatous degeneration 63

Biochemical evaluation

The issue on the necessity of hormonal evaluation of adrenal myelolipomas is debated 59. Future studies are required to clarify the approach to hormonal assessment in patients with myelolipomas 66.

• Myelolipomas, themselves are thought to be predominantly non-functional 67, but may be associated with hormonal disorders 59 (e.g Congenital Adrenal Hyperplasia) and other adrenal tumours 
• Patients with congenital adrenal hyperplasia exhibit a higher prevalence of adrenal myelolipomas than other patient groups, and are at risk of developing large and bilateral lesions 66
• Although a 2003 NIH report 68 states that, should the physician discover a myelolipoma, compulsory workup for additional metabolically active lesions is not required, other authors differ 66, 70. A 2021 review 66 states that, based on expert opinion, hormonal workup should be considered, informed by the clinical presentation. (Note: The hormonal workup is not for the myelolipoma itself, but for concomitant adenomas or hyperplasia).
• Similarly, the majority of international guidelines recommend hormone testing for all adrenal incidentalomas, but are not very clear, or differ, on the role of testing specifically in myelolipomas 59
• Large  (>4cm) and bilateral adrenal myelolipomas are more likely to be associated with hormonal disturbance 66
• The clinical picture should be considered to be the major factor in determining the necessity for hormonal work-up 59

• Adrenal lesions indeterminate on a non-contrast CT scan can be assessed with chemical shift MRI. 
• Chemical shift MRI exploits the different frequency of protons in water and fat to detect microscopic fat; high content of intracellular lipid usually causes loss of signal intensity on opposed-phase images compared to in-phase images 
• When microscopic fat is identified by signal intensity drop on opposed-phase MRI, a lipid-rich adenoma can be diagnosed
•  A caveat is that heterogeneous signal intensity drop may indicate very small amounts of microscopic fat in phaeochromocytoma, adrenal cortical carcinoma, and some metastases 71, 72
• Advantages of MRI over CT include lack of ionising radiation, lack of iodine-based contrast media, and its superior tissue contrast resolution
• Disadvantages compared to CT include longer scanning times and patient claustrophobia
• A 2019 systematic review/meta-analysis reported the pooled sensitivity of CSI for adenoma was 0.94 and pooled specificity was 0.95 73
• Chemical shift MRI and washout CT have similar accuracy for evaluating adrenal lesions that are indeterminate on non-contrast CT 74

• • 75% of incidental adrenal nodules are adenomas. They contain a variable degree of intra-cytoplasmic lipid, leading to the imaging features indicated below
  • A mass that is homogeneous, well-circumscribed and measures <10 HU can be confidently diagnosed as a lipid-rich benign adenoma - 71% sensitivity and >99% specificity 75, 76 (N.B there has been a recent suggestion to increase the upper CT attenuation threshold to 20 Hounsfield units for lesions <4cm in size to replace the traditionally accepted 10HU threshold in excluding malignancy - Click here for important note
  • Patients who have benign features on CT have benign pathology 74
  • Approximately 30% of benign adenomas have attenuation >10HU (i.e. lipid-poor)
  • Typical features of myelolipomas and benign cysts can be identified on non-contrast CT Adrenal Myelolipomas

Dual Energy CT (DECT)

• Recent studies have shown that DECT holds considerable promise in improving the diagnostic confidence, reduce radiation exposure, and streamline the investigation of patients with adrenal incidentalomas 77, 78 decreasing the need for additional CT examinations to characterize IALs detected on single-phase contrast-enhanced CT 79
• Further studies are awaited

• AWCT has long been considered the mainstay of diagnosis for lesions that do not fit the criteria for benignity on non-contrast CT
• AWCT protocol consists of measuring non-contrast attenuation , followed by initial post-contrast enhancement and delayed (15 minutes) attenuation 38
• Absolute percentage washout ([enhanced - delayed]/[enhanced - unenhanced] x 100) greater than 60% or relative percentage washout ([enhanced - delayed]/enhanced x 100]) greater than 40% have been used to support the diagnosis of a benign lesion 4, 74
• However , the utility of AWCT has been questioned 6, 8, 52, 56, 80 with suggestions that its use should be ceased 6 Click here for important note

Lesions <10 mm

• Modern imaging can detect nodules < 10 mm
• However, some authorities (eg. Canadian Urological Association, 2023, ACR , 2017, Society of Abdominal Radiology, 2023) 2-5 limit the definition of IALs to adrenal masses > 10 mm, as does a recent article by Seow et al 6. The ACR goes further stating that a IAL <1 cm in the short axis need not be pursued 5.
• However, a study by Kim et al. 3 reported that a lesion of long axis ≥10 mm is a reasonable cutoff for determining adrenal abnormality 3
• The management of lesions <10 mm is  unclear; there is no literature supporting further evaluation of lesions <10 mm 38
• Some consensus guidelines suggest follow up clinically, but not radiologically, unless a biochemical abnormality is discovered 15. However, it is uncertain whether in the absence of clinical indicators all these patients should be investigated biochemically.
• Management of lesions <10 mm should be influenced by the age and clinical context