Adrenal Washout Calculator & Report Generator for CT
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More about the Adrenal Washout Calculator
Characterizing Indeterminate Adrenal Nodules on CT
The Adrenal Washout Calculator supports CT characterization of indeterminate adrenal nodules by quantifying contrast enhancement and delayed washout. Adrenal incidentalomas are commonly encountered on cross sectional imaging, with prevalence estimates often cited in the low single digits in adult populations and increasing with age [2]. The key clinical goal is to help distinguish benign adrenal adenomas from entities that may require different management, including adrenocortical carcinoma, pheochromocytoma, and metastatic disease [1] [4].
Unenhanced CT characterizes many lipid rich adenomas using a threshold of 10 Hounsfield units or less, which is associated with high specificity in appropriate clinical contexts [1]. A subset of adenomas are lipid poor and measure above this threshold, which is a frequent practical problem. In those cases, washout analysis provides a structured method for evaluating enhancement kinetics using multiphasic CT measurements [3] [5].
Physiologic Rationale for Washout Measurements
Washout analysis reflects two broad lesion characteristics: intracellular lipid content and contrast distribution within tumor microvasculature and interstitium.
Intracytoplasmic lipid. Lipid rich adenomas contain variable amounts of intracellular fat related to steroid synthesis, which lowers unenhanced attenuation. An unenhanced value of 10 HU or less is commonly used as a benign imaging feature when lesion morphology and clinical context are appropriate [1] [3].
Microvascular kinetics. Adenomas often show rapid enhancement and relatively faster contrast clearance compared with many nonadenomas. Malignant lesions can demonstrate heterogeneous enhancement and more prolonged contrast retention, although overlap exists and interpretation should consider lesion morphology, size, and clinical risk factors [4] [5].
| Feature | Adrenal Adenoma | Adrenal Malignancy or Nonadenoma |
|---|---|---|
| Cellular composition | Clear or compact cells, variable lipid content | Variable cellularity, may be pleomorphic depending on pathology |
| Capillary architecture | Often relatively uniform | May be irregular with heterogeneous perfusion |
| Enhancement pattern | Often rapid enhancement with higher washout | Variable enhancement, washout can be slower or heterogeneous |
CT Protocol and ROI Technique
Accurate use of the Adrenal Washout Calculator depends on standardized acquisition and consistent region of interest technique.
Unenhanced phase. Establishes baseline attenuation. Homogeneous lesions measuring 10 HU or less are commonly managed as benign appearing in many algorithms, assuming appropriate clinical and endocrine evaluation [1].
Early enhanced phase. Typically acquired in a portal venous phase around 60 to 75 seconds, although local protocols vary. Arterial phase imaging may be helpful when hypervascular lesions are a concern, including pheochromocytoma [4].
Delayed phase. Delayed imaging at 10 to 15 minutes is commonly used. Both 10 minute and 15 minute protocols are described in the literature, and diagnostic performance depends on technique and patient population [4] [5].
ROI placement. Place the ROI over a substantial portion of the enhancing solid component while excluding calcification, macroscopic fat, hemorrhage, necrosis, and cystic change. Heterogeneous lesions reduce reliability of numeric thresholds and should be interpreted with morphology and clinical context in mind [3] [5].
| Parameter | Required Measurements | Commonly Used Thresholds |
|---|---|---|
| Absolute Percentage Washout | Unenhanced HU, Enhanced HU, Delayed HU | At least 60 percent is commonly used in many protocols [5] |
| Relative Percentage Washout | Enhanced HU, Delayed HU | At least 40 percent is commonly used in many protocols [5] |
| Delayed Washout Assessment at Fixed Delay | Enhanced HU and Delayed HU at a defined delay time | Thresholds vary by protocol and delay time, and should be interpreted alongside morphology [4] [5] |
Clinical Mimics and Diagnostic Pitfalls
Washout values overlap across pathologies, so findings should be integrated with the overall imaging pattern and clinical risk profile.
Pheochromocytoma. Some pheochromocytomas can demonstrate washout values within ranges often associated with adenoma. Marked arterial enhancement, cystic or hemorrhagic components, and relevant symptoms should prompt biochemical correlation [1] [4].
Adrenocortical carcinoma. Larger size, irregular margins, heterogeneous enhancement, necrosis, and locally invasive features increase concern. Lesions above common size thresholds, such as 4 cm, often warrant multidisciplinary review even when numeric washout values appear benign [1].
Metastases. Hypervascular metastases, including those from renal cell carcinoma or hepatocellular carcinoma, may enhance briskly and show partial washout. Prior malignancy history and whole body disease context are central to interpretation [1].
Guideline Context and Clinical Integration
Contemporary guidance emphasizes individualized risk stratification and careful integration of imaging with endocrine evaluation [1]. Homogeneous lesions with low unenhanced attenuation may not require additional imaging follow up in appropriately evaluated patients, while indeterminate lesions often require a tailored approach based on clinical context.
The Adrenal Washout Calculator is best used as decision support that complements morphologic assessment, endocrine testing, and clinical judgment. It is not a substitute for comprehensive evaluation.
Internal linking opportunities: Adrenal incidentaloma imaging resources, Abdominal CT reporting templates, Other abdominal imaging calculators.
Emerging Techniques: Dual Energy CT and Quantitative Imaging
Dual energy CT can generate virtual unenhanced datasets and iodine maps that may assist lesion characterization in selected workflows. Measured values can differ from true unenhanced attenuation, and protocol specific performance should be understood before routine adoption [7].
Quantitative imaging approaches, including radiomics, have shown investigational potential for adrenal lesion classification, but reproducibility and standardization remain important considerations for clinical implementation.
Frequently Asked Questions (FAQs)
Can the Adrenal Washout Calculator be used when unenhanced attenuation is 10 HU or less?
For a homogeneous lesion measuring 10 HU or less on unenhanced CT, the imaging appearance is commonly considered consistent with lipid rich adenoma in appropriate clinical settings, and additional washout analysis is often not required unless other concerning features are present [1] [3].
Why are delayed phases at 10 minutes or 15 minutes used?
Both 10 minute and 15 minute delayed acquisitions are described. Published protocols demonstrate that diagnostic performance depends on consistent timing, technique, and patient population. Your local protocol should be applied consistently when using numeric thresholds [4] [5].
How should discordant findings be interpreted, such as very high arterial enhancement with elevated washout values?
Marked early enhancement can raise concern for hypervascular lesions, including pheochromocytoma. In such situations, correlation with clinical features and biochemical testing is important before management decisions are made [1] [4].
Is washout analysis sufficient for masses larger than 4 cm?
Size is a clinically relevant risk factor. Masses larger than 4 cm commonly warrant multidisciplinary discussion, particularly when morphology is heterogeneous or other suspicious features are present, even if washout parameters fall within commonly used adenoma thresholds [1].
How do virtual unenhanced values compare with true unenhanced attenuation?
Virtual unenhanced values derived from dual energy CT can differ from true unenhanced measurements. Thresholds may require protocol specific evaluation, and interpretation should account for the acquisition method and reconstruction technique [7].
- Fassnacht M, Tsagarakis S, Terzolo M, et al. European Society of Endocrinology clinical practice guidelines on the management of adrenal incidentalomas, in collaboration with the European Network for the Study of Adrenal Tumors. Eur J Endocrinol. 2023;189(1):G1-G42. https://doi.org/10.1093/ejendo/lvad066
- Song JH, Chaudhry FS, Mayo-Smith WW. The incidental adrenal mass on CT: prevalence of adrenal disease in 973 consecutive patients. AJR Am J Roentgenol. 2008. https://doi.org/10.2214/AJR.07.2799
- Caoili EM, Korobkin M, Francis IR, et al. Adrenal masses: characterization with combined unenhanced and delayed enhanced CT. Radiology. 2002;222(3):629-633. https://doi.org/10.1148/radiol.2223010766
- Blake MA, Kalra MK, Sweeney AT, et al. Distinguishing benign from malignant adrenal masses: multi-detector row CT protocol with 10-minute delay. Radiology. 2006;238(2):578-585. https://doi.org/10.1148/radiol.2382041514
- Szolar DH, Kammerhuber FH. Adrenal adenomas and nonadenomas: assessment of washout at delayed contrast-enhanced CT. Radiology. 1998;207(2):369-375. https://doi.org/10.1148/radiology.207.2.9577483
- Korobkin M, Brodeur FJ, Francis IR, et al. CT time-attenuation washout curves of adrenal adenomas and nonadenomas. AJR Am J Roentgenol. 1998;170(3):747-752. https://doi.org/10.2214/ajr.170.3.9490968
- McCollough CH, Leng S, Yu L, Fletcher JG. Dual- and multi-energy CT: principles, technical approaches, and clinical applications. Radiology. 2015;276(3):637-653. https://doi.org/10.1148/radiol.2015142631
PGY-5 Radiology and Nuclear Medicine Resident Physician, UT Southwestern Medical Center, USA
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