Imaging Pearls ❯ Adrenal ❯ Imaging Techniques
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- For over 20 years, the two key tenets of adrenal incidentaloma (AI) evaluation have been the upper threshold of 10 Hounsfield units (HU) on noncontrast CT (ncCT) to delineate benignity, and the utilisation of adrenal washout CT (AWCT) to evaluate those above this cutoff. In light of growing recent evidence that challenges these two traditional principles, as well as re-evaluation of the data that led to their acceptance, we conclude that neither of these mainstays of adrenal CT remains relevant in modern AI diagnostic workup. With an appropriate definition of an incidentaloma and endocrine assessment for the majority of adrenal lesions, our analysis establishes that the use of AWCT should be ceased in the assessment of AIs, and that a 20 HU attenuation threshold for lesions < 4 cm should replace the traditional 10 HU threshold to exclude malignancy in this patient population. We therefore propose new recommendations for the management of AIs based primarily on CT attenuation and lesion size on ncCT.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136 - Critical relevance statement
Increasing the CT attenuation threshold to 20 HU for lesions < 4 cm and eliminating washout CT for true adrenal incidentalomas, together with recommendations for endocrine assessment, will significantly decrease the over-investigation of overwhelmingly benign adrenal lesions, whilst confidently excluding malignancy.
Key Points
● True incidentalomas exclude current or prior extra-adrenal malignancy and clinically suspected adrenal disease.
● Adrenal washout CT was never proven in the malignancy-sparse true incidentaloma population.
● Hormonal correlation in parallel with < 20 HU and < 4 cm thresholds of homogeneous lesions on noncontrast CT excludes malignancy.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136 
- Accordingly, we propose that in true AIs, combined 20 HU and 4 cm cut-offs exclude malignancy, and replace the established 10 HU threshold. We also highlight that even in those > 20 HU but < 4 cm, or > 4 cm but < 20 HU, malignancy rates are also extremely low.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136 - Radiology reports should include a recommendation to perform a hormonal evaluation for all remaining AIs, which will identify nearly all PCC, as well as most ACC. Additionally, endocrine correlation identifies subclinically functional adenomas (including MACS), 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.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136 - On ncCT , homogeneous AIs ≤ 20 HU and ≤ 4 cm, or as per existing guidelines, < 10 HU and any size, are considered benign (Category-1), with no imaging follow-up required. AIs which are > 20 HU and 1–4 cm, OR 10–20 HU but > 4 cm, are highly likely benign (Category-2), and therefore 6–12 month ncCT is currently suggested as supported by most AI guidelines, purely to identify growth or stability. Those > 20 HU AND > 4 cm are considered higher risk (Category-3), with multidisciplinary meeting or surgical referral recommended, albeit acknowledging that most will still be of benign aetiology. As discussed prior, a more cautious approach is advised if AIs are > 40 HU and/or > 6 cm.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136 
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136- Whilst the 10 HU threshold and AWCT have been ingrained in the radiology mindset over the last 2–3 decades, we believe it is now a timely end of an era for both these tenets of AI imaging. First, there is now sufficient evidence that a 20 HU threshold in AIs < 4 cm can safely replace the prior 10 HU limit. Second, due to its inherent inaccuracy and the extremely low incidence of malignancy in true AIs, AWCT has no role in the evaluation of ALs in patients without prior/current malignancy or suspected adrenal disease. Instead, AIs can be managed with ncCT, in parallel with endocrine testing, which complementarily improves detection of benign(and rarely malignant) hormonally active lesions.
Washed up: the end of an era for adrenal incidentaloma CT
James H. Seow et al.
Insights into Imaging ( 2025) 16:136
- OBJECTIVES: To compare robot-assisted laparoscopic adrenalectomy (RALA) and open adrenalectomy (OA) with regard to intra-operative complications, peri-operative outcome and cost effectiveness.
CONCLUSIONS: The study showed that RALA was safe and cost-effective compared with OA. Increasing experience leads to similar operating times, putting high-volume centres at an advantage. Robot-assisted vs open adrenalectomy: evaluation of cost-effectiveness and peri-operative outcome.
Probst KA et al. BJU Int. 2016 Dec;118(6):952-957 - RESULTS: As a result of the matching process, patient groups did not differ in their main characteristics. Length of hospital stay was shorter for RALA than for OA (11.1 ± 4.8 vs 6.8 ± 1.2 days; P < 0.01) as was IMC treatment (2.3 ± 1.7 vs 1.2 ± 0.4 days; P < 0.01). The mean operating time was longer for RALA (128.5 ± 46.5 vs 102.2 ± 44.5 min; P = 0.03), but the last 10 RALA procedures (mean: 97.1 ± 35.2 min) were similar to OA. The rate of complications was similar in the two groups. Estimated costs were €8 627.5 for OA and €7 334 for RALA.
Robot-assisted vs open adrenalectomy: evaluation of cost-effectiveness and peri-operative outcome.
Probst KA et al. BJU Int. 2016 Dec;118(6):952-957 - PURPOSE: To evaluate the surgical feasibility of retroperitoneal laparoscopic adrenalectomy for tumors exceeding 5 cm.
RESULTS: The estimated blood loss (271.75 ± 232.98 mL vs. 367.24 ± 275.11 mL; p = 0.037), time to ambulation (1.60 ± 0.49 days vs. 1.89 ± 0.31 days; p = 0.001), and postoperative hospitalization (7.88 ± 3.08 days vs. 9.264 ± 3.10 days; p = 0.012) were significantly higher in group II. The operation time and hemoglobin level change were not statistically different between groups. Blood transfusions were performed in 3 patients from group I and 6 patients from group II (5.3 vs. 7.9 %; p = 0.449). No patients experienced conversion to open surgery.
CONCLUSIONS: Retroperitoneal laparoscopic adrenalectomy can be used in patients with tumors larger than 5 cm. Is larger tumor size a contraindication to retroperitoneal laparoscopic adrenalectomy?
Hwang I et al. World J Urol. 2014 Jun;32(3):723-8
- “The following dimensions were measured: the maximum width perpendicular to the long axis of the body of the gland, and maximum width of the medial and lateral limbs. The average measurements for the right adrenal gland were: maximum width 0.61 cm (S.D. 0.2), width of the medial limb 0.28 cm (S.D. 0.08), and width of the lateral limb 0.28 cm (S.D. 0.06). The average measurements for the left adrenal gland were: maximum width 0.79 cm (S.D. 0.21), width of the medial limb 0.33 cm (S.D. 0.09), and width of the lateral limb 0.30 cm (S.D. 0.10)”
The size of normal adrenal glands on computed tomography.
Vincent JM1 et al.
Clin Radiol. 1994 Jul;49(7):453-5. - “The adrenal glands are small organs, weighing approximately 5.0 g each, on average, and measuring approximately 30.0 mm in width, 50.0 mm in length, and up to 10.0 mm in thickness. They have a linear "V’ or "Y’ shape and are located anterosuperiorly to the kidneys.”
CT and MRI of Adrenal Masses
Antonio CA et al.
Appl Radiol. 2006;35(8)10-26 - “ The length, width, thickness of right adrenal body, thickness of medial limb and lateral limb were, respectively, 34.02 +/- 2.12 mm, 10.91 +/- 0.89 mm, 5.82 +/- 0.26 mm, 2.78 +/- 0.08 mm, 2.62 +/- 0.06 mm, whereas the measurements of left adrenal gland were 28.31 +/- 2.46 mm, 18.40 +/- 1.06 mm, 6.84 +/- 0.24 mm, 3.02 +/- 0.08 mm, 2.86 +/- 0.07 mm, respectively. The coronal plane has superior advantage in showing the bilateral adrenal glands. The shapes of adrenal glands are various, whereas the range of adrenal thickness is quite narrow. The thickness of adrenal medial and lateral limbs, especially the thickness of lateral limb are useful for the diagnosis of the bilateral adrenocortical disease.”
“ The length, width, thickness of right adrenal body, thickness of medial limb and lateral limb were, respectively, 34.02 +/- 2.12 mm, 10.91 +/- 0.89 mm, 5.82 +/- 0.26 mm, 2.78 +/- 0.08 mm, 2.62 +/- 0.06 mm, whereas the measurements of left adrenal gland were 28.31 +/- 2.46 mm, 18.40 +/- 1.06 mm, 6.84 +/- 0.24 mm, 3.02 +/- 0.08 mm, 2.86 +/- 0.07 mm, respectively.”
Sectional anatomy of the adrenal gland in the coronal plane.
Ma G et al.
Surg Radiol Anat. 2008 May;30(3):271-80. - “The coronal plane has superior advantage in showing the bilateral adrenal glands. The shapes of adrenal glands are various, whereas the range of adrenal thickness is quite narrow. The thickness of adrenal medial and lateral limbs, especially the thickness of lateral limb are useful for the diagnosis of the bilateral adrenocortical disease.”
Sectional anatomy of the adrenal gland in the coronal plane.
Ma G et al.
Surg Radiol Anat. 2008 May;30(3):271-80. - “ CT body scans of 60 random patients without evidence of adrenal disease were reviewed to determine the location, size, and shape of both normal adrenal glands. Both glands were clearly delineated in 78% of the patients evaluated. The length, width, and thickness of adrenal glands as measured by computed tomography were similar to comparable measurements from surgical and autopsy studies.”
Computed tomography of the normal adrenal glands.
Montagne JP et al.
AJR 1978 May; 130(5):963-6
- Washout Characteristics
-Adenomas washout more rapidly than metastases
-Pheochromocytoma can exhibit high washout levels when hypervascular - Relative Percentage Washout
100 x (Venous HU – Delayed HU)
Venous HU
> 40% ~ adenoma - Absolute Percentage Washout
100 x (Venous HU – Delayed HU)
Venous HU-Precontrast HU
> 60% ~ adenoma - ASIR: Potential Limitations
- Takes longer than standard algorithms to reconstruct CT data by a factor of up to 30%
- Image smoothing may lead to lack of lesion recognition. It is not clear whether this means missed lesions. "The ASIR reconstruction algorithm is a promising technique for providing diagnostic quality CT images at significantly reduced radiation doses."
Innovations in CT Dose Reduction Strategy: Application of the Adaptive Statistical Iterative Reconstruction Algorithm
Silva AC et al.
AJR 2010;194: 191-199"Currently, increased noise limits the evaluation of thin reconstructed images (<2.5 mm) in abdominal imaging."
Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study
Hara AK et al.
AJR 2009; 193:764-771"Low dose CT with adaptive statistical iterative reconstruction and routine dose CT had identical results for low contrast resolution and nearly identical results for overall image quality. Spatial resolution was better with routine dose CT."
Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study
Hara AK et al.
AJR 2009; 193:764-771"These preliminary results support body CT dose index reductions of 32-65% when adaptive statistical iterative reconstruction is used. Studies with larger statistical samples are needed to confirm these findings."
Iterative Reconstruction Technique for Reducing Body Radiation Dose at CT: Feasibility Study
Hara AK et al.
AJR 2009; 193:764-771- Three dimensional volume rendered CT successfully displayed the relationship of adrenal masses to adjacent structures and organs before laparoscopic adrenalectomy. Three Dimensional Volume Rendered Helical CT before Laparoscopic Adrenalectomy Hurley ME et al. Radiology 2003; 229:581-586