What Hounsfield units are required to evaluate an adrenal lesion for pheochromocytoma (pheo)?

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From the Guidelines

Pheochromocytoma evaluation requires adrenal lesions with Hounsfield units (HU) less than 10.

Key Points

  • HU threshold: A threshold value of 10 HU is generally accepted as a cutoff value for a region of interest obtained over the lesion to differentiate benign from malignant adrenal tumors 1.
  • CT evaluation: Nonenhanced CT is a relatively inexpensive yet highly specific test for differentiating adenomas and some benign nonadenomas from malignant lesions 1.
  • Delayed enhanced CT: Delayed enhanced CT is better able to distinguish adenomas and metastases, with a sensitivity and specificity of greater than 95% and 97%, respectively, after a delay of 15 minutes 1.
  • MRI: MRI offers a preferential application for the suspicion of pheochromocytoma due to the risk of a hypertensive crisis after infusion of i.v. contrast medium for CT 1.
  • Pheochromocytoma diagnosis: The diagnosis of pheochromocytoma is based on clinical presentation, biochemical tests (e.g., plasma and urine metanephrine and normetanephrine levels), and imaging studies (e.g., CT, MRI, MIBG scintigraphy) 1.

Evidence Summary

The evidence suggests that Hounsfield units (HU) less than 10 are required to evaluate an adrenal lesion for pheochromocytoma (pheo) 1. Nonenhanced CT and delayed enhanced CT are useful imaging modalities for differentiating benign from malignant adrenal tumors 1. MRI is also a useful modality, particularly for suspected pheochromocytoma 1. The diagnosis of pheochromocytoma is based on a combination of clinical presentation, biochemical tests, and imaging studies 1.

Clinical Implications

In clinical practice, adrenal lesions with HU less than 10 on nonenhanced CT should be further evaluated for pheochromocytoma using biochemical tests and imaging studies. Delayed enhanced CT and MRI can be useful adjuncts to nonenhanced CT for differentiating benign from malignant adrenal tumors. The diagnosis of pheochromocytoma requires a combination of clinical presentation, biochemical tests, and imaging studies.

From the Research

Hounsfield Units for Evaluating Adrenal Lesions for Pheochromocytoma

To evaluate an adrenal lesion for pheochromocytoma (pheo), the following Hounsfield units (HU) are considered:

  • A cutoff of >10 HU has a 100% sensitivity for pheochromocytoma 2, 3
  • A cutoff of >15 HU has a sensitivity of 100% for pheochromocytoma 2
  • A cutoff of >20 HU has a sensitivity of 99% for pheochromocytoma 2
  • Lesions with an attenuation value ≤10 HU on unenhanced CT images have a low likelihood of being pheochromocytoma 3, 4
  • Lesions with an attenuation value >10 HU may require further evaluation, including biochemical testing or MRI 4, 5
  • A threshold of 130 HU can be used to identify pheochromocytoma, with a sensitivity of 38% and specificity of 100% 6

Key Findings

  • Unenhanced CT imaging can be used to rule out pheochromocytoma in adrenal lesions with low attenuation (<10 HU) 2, 3
  • The combination of tumor size, high lipid content, and hyperintensity in T2 sequence on MRI can improve diagnostic accuracy for pheochromocytoma 4
  • Modified CT criteria, including lesion attenuation, absolute percentage washout, and relative percentage washout, can improve diagnostic performance in distinguishing pheochromocytoma from adrenal adenoma 5

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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