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Differentiation of adrenal adenoma and nonadenoma in unenhanced CT: new optimal threshold value and the usefulness of size criteria for differentiation.

Park SH, Kim MJ, Kim JH, Lim JS, Kim KW - Korean J Radiol (2007 Jul-Aug)

Bottom Line: The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test.The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.The adenomas had a significantly (p < 0.05) smaller diameter (2.44+/-1.24 cm) than the nonadenomas (5.09+/-2.37 cm).

View Article: PubMed Central - PubMed

Affiliation: Department of Diagnostic Radiology and Research Institute of Radiological Science, Severance Hospital, Yonsei University College of Medicine, 134 Shinchondong, Seodaemungu, Seoul 120-752, Korea. kimnex@yumc.yonsei.ac.kr.

ABSTRACT

Objective: To determine the optimal threshold for the attenuation values in unenhanced computed tomography (CT) and assess the value of the size criteria for differentiating between an adrenal adenoma and a nonadenoma.

Materials and methods: The unenhanced CT images of 45 patients at our institution, who underwent a surgical resection of an adrenal masses between January 2001 and July 2005, were retrospectively reviewed. Forty-five adrenal masses included 25 cortical adenomas, 12 pheochromocytomas, three lymphomas, and five metastases confirmed by pathology were examined. The CT images were obtained at a slice thickness of 2 mm to 3 mm. The mAs were varied from 100 to 160 and 200 to 280, while the 120 KVp was maintained in all cases. The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy at thresholds of 10 HU, 20 HU, and 25 HU were compared. The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.

Results: The twenty-five adenomas showed significantly lower (p < 0.05) attenuation values (mean+/-SD; 16.3+/-14.9) than the nonadenomas (38.1+/-6.8). Nineteen (90%) of the 20 nonadenomas had attenuation values ranging from 30 to 50 HU. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for diagnosing adenomas were 36%, 100%, 100%, 56%, and 64%, respectively, at a threshold of 10 HU; 60%, 100%, 100%, 67%, and 78%, respectively, at a threshold of 20 HU; and 72%, 95%, 95%, 73%, and 82%, respectively, at a threshold of 25 HU. The adenomas had a significantly (p < 0.05) smaller diameter (2.44+/-1.24 cm) than the nonadenomas (5.09+/-2.37 cm). The size criteria using a diameter of 4-6 cm showed a sensitivity > 90% but a specificity < 70%. Size criteria of 2 or 3 cm had a high specificity of 100% and 80% but a low sensitivity of 20% and 60%.

Conclusion: The threshold attenuation values of 20 or 25 HU in the unenhanced CT appear optimal for discriminating an adrenal adenoma from a nonadenoma. The size criteria are of little value in differentiating adrenal masses because of their low specificity or low sensitivity.

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Scattergram of the attenuation values in the unenhanced CT of 25 adenomas and each group of 20 nonadenomas (NA-L: lymphoma, NA-M: metastasis, NA-P: pheochromocytoma). Note that all masses with a HU < 20 were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20, and eighteen (90%) of the nonadenomas had attenuation values > 30 HU.
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Figure 1: Scattergram of the attenuation values in the unenhanced CT of 25 adenomas and each group of 20 nonadenomas (NA-L: lymphoma, NA-M: metastasis, NA-P: pheochromocytoma). Note that all masses with a HU < 20 were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20, and eighteen (90%) of the nonadenomas had attenuation values > 30 HU.

Mentions: Figure 1 shows a scattergram of the attenuation values on the unenhanced CT of 25 adenomas and each group of 20 nonadenomas. The attenuation values were negative in four (16%) adenomas, > 10 HU in 16 (64%) adenomas, and > 30 HU in seven (28%) adenomas. These seven attenuation values > 30 HU overlapped with the range of nonadenomas. All masses with attenuation < 20 HU were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20. Eighteen (90%) nonadenomas had attenuation values > 30 HU. The attenuation values for the pheochromocytomas ranged from 36.6 HU to 49.1 HU, with a mean value of 40.0 ± 5.7 HU. All the metastases had values > 30 HU ranging from 33.4 HU to 36.6 HU with a mean value of 35.3 ± 1.3 HU. The attenuation values of the three lymphomas were the lowest among the nonadenoma groups, ranging from 20.6 HU to 32.7 HU with a mean value of 25.6 ± 6.1 HU. Table 1 shows the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy calculated for each threshold value. At a threshold value of 10 HU, the sensitivity (36%) and NPV (56%) values were lowest, even though the specificity and PPV were 100%. At a threshold value of 20 HU, the sensitivity and NPV were increased to 60%, while the specificity and positive predictive value were maintained at 100%. At a threshold value of 25 HU, the sensitivity was further increased to 72%, but the specificity (95%) and positive predictive value (95%) decreased.


Differentiation of adrenal adenoma and nonadenoma in unenhanced CT: new optimal threshold value and the usefulness of size criteria for differentiation.

Park SH, Kim MJ, Kim JH, Lim JS, Kim KW - Korean J Radiol (2007 Jul-Aug)

Scattergram of the attenuation values in the unenhanced CT of 25 adenomas and each group of 20 nonadenomas (NA-L: lymphoma, NA-M: metastasis, NA-P: pheochromocytoma). Note that all masses with a HU < 20 were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20, and eighteen (90%) of the nonadenomas had attenuation values > 30 HU.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2627166&req=5

Figure 1: Scattergram of the attenuation values in the unenhanced CT of 25 adenomas and each group of 20 nonadenomas (NA-L: lymphoma, NA-M: metastasis, NA-P: pheochromocytoma). Note that all masses with a HU < 20 were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20, and eighteen (90%) of the nonadenomas had attenuation values > 30 HU.
Mentions: Figure 1 shows a scattergram of the attenuation values on the unenhanced CT of 25 adenomas and each group of 20 nonadenomas. The attenuation values were negative in four (16%) adenomas, > 10 HU in 16 (64%) adenomas, and > 30 HU in seven (28%) adenomas. These seven attenuation values > 30 HU overlapped with the range of nonadenomas. All masses with attenuation < 20 HU were adenomas. Among the 20 nonadenomas, none had an attenuation value < 20. Eighteen (90%) nonadenomas had attenuation values > 30 HU. The attenuation values for the pheochromocytomas ranged from 36.6 HU to 49.1 HU, with a mean value of 40.0 ± 5.7 HU. All the metastases had values > 30 HU ranging from 33.4 HU to 36.6 HU with a mean value of 35.3 ± 1.3 HU. The attenuation values of the three lymphomas were the lowest among the nonadenoma groups, ranging from 20.6 HU to 32.7 HU with a mean value of 25.6 ± 6.1 HU. Table 1 shows the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy calculated for each threshold value. At a threshold value of 10 HU, the sensitivity (36%) and NPV (56%) values were lowest, even though the specificity and PPV were 100%. At a threshold value of 20 HU, the sensitivity and NPV were increased to 60%, while the specificity and positive predictive value were maintained at 100%. At a threshold value of 25 HU, the sensitivity was further increased to 72%, but the specificity (95%) and positive predictive value (95%) decreased.

Bottom Line: The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test.The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.The adenomas had a significantly (p < 0.05) smaller diameter (2.44+/-1.24 cm) than the nonadenomas (5.09+/-2.37 cm).

View Article: PubMed Central - PubMed

Affiliation: Department of Diagnostic Radiology and Research Institute of Radiological Science, Severance Hospital, Yonsei University College of Medicine, 134 Shinchondong, Seodaemungu, Seoul 120-752, Korea. kimnex@yumc.yonsei.ac.kr.

ABSTRACT

Objective: To determine the optimal threshold for the attenuation values in unenhanced computed tomography (CT) and assess the value of the size criteria for differentiating between an adrenal adenoma and a nonadenoma.

Materials and methods: The unenhanced CT images of 45 patients at our institution, who underwent a surgical resection of an adrenal masses between January 2001 and July 2005, were retrospectively reviewed. Forty-five adrenal masses included 25 cortical adenomas, 12 pheochromocytomas, three lymphomas, and five metastases confirmed by pathology were examined. The CT images were obtained at a slice thickness of 2 mm to 3 mm. The mAs were varied from 100 to 160 and 200 to 280, while the 120 KVp was maintained in all cases. The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy at thresholds of 10 HU, 20 HU, and 25 HU were compared. The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.

Results: The twenty-five adenomas showed significantly lower (p < 0.05) attenuation values (mean+/-SD; 16.3+/-14.9) than the nonadenomas (38.1+/-6.8). Nineteen (90%) of the 20 nonadenomas had attenuation values ranging from 30 to 50 HU. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for diagnosing adenomas were 36%, 100%, 100%, 56%, and 64%, respectively, at a threshold of 10 HU; 60%, 100%, 100%, 67%, and 78%, respectively, at a threshold of 20 HU; and 72%, 95%, 95%, 73%, and 82%, respectively, at a threshold of 25 HU. The adenomas had a significantly (p < 0.05) smaller diameter (2.44+/-1.24 cm) than the nonadenomas (5.09+/-2.37 cm). The size criteria using a diameter of 4-6 cm showed a sensitivity > 90% but a specificity < 70%. Size criteria of 2 or 3 cm had a high specificity of 100% and 80% but a low sensitivity of 20% and 60%.

Conclusion: The threshold attenuation values of 20 or 25 HU in the unenhanced CT appear optimal for discriminating an adrenal adenoma from a nonadenoma. The size criteria are of little value in differentiating adrenal masses because of their low specificity or low sensitivity.

Show MeSH
Related in: MedlinePlus