Physiology of renal medullary tip hyperattenuation at unenhanced CT: Urinary specific gravity and the NaCl concentration gradient

Christopher T. Hsu, Zhen J. Wang, Alan S L Yu, Robert G. Gould, Yanjun Fu, Bonnie N. Joe, Aliya Qayyum, Richard S. Breiman, Fergus Coakley, Benjamin M. Yeh

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Abstract

Purpose: To retrospectively investigate the physiology of renal medullary tip hyperattenuation at unenhanced computed tomography (CT). Materials and Methods: This retrospective single-institution study was IRB approved and HIPAA compliant. Informed consent was waived. One hundred consecutive patients (53 women, mean age, 52 years; 47 men, mean age, 48 years; P = .39) without and 34 (11 women, mean age, 49 years; 23 men, mean age, 45 years; P = .54) with unilateral ureteral obstruction underwent contemporaneous urinalysis and unenhanced CT. At CT, bladder urine attenuation was measured and two readers recorded the presence of renal medullary tip hyperattenuation. For obstructed kidneys (n = 34), renal pelvic urine attenuation was also recorded. The presence of medullary tip hyperattenuation was correlated with urinary specific gravity. To investigate the physiologic basis of medullary tip hyperattenuation, attenuations for NaCl and urea phantoms (range, 0-2000 mosm/kg) were recorded and correlated to solute concentrations by using linear regression. Results: Patients with renal medullary tip hyperattenuation seen at CT had higher mean urinary specific gravity (1.023 and 1.022 for readers 1 and 2, respectively) than those without (1.015 and 1.016, respectively, both P <.05). The specific gravity correlated with higher urine attenuation (r = 0.40, P <.001). For the 34 patients with unilateral urinary obstruction, medullary tip hyperattenuation was less commonly seen in obstructed (two kidneys each for both readers) than nonobstructed (11 and 15 kidneys, respectively, both P <.005) kidneys and mean urine attenuation was lower in the obstructed renal pelvis (7.4 HU) than in the bladder (11.4 HU) (P <.005). Phantoms showed a 3.6-HU increase per 100-mosm/kg increase in NaCl concentration (r = 0.99, P <.001) but no change in attenuation with different urea concentrations. Conclusion: Renal medullary tip hyperattenuation at unenhanced CT reflects increased urinary specific gravity, likely related to high medullary tip NaCl concentrations.

Original languageEnglish (US)
Pages (from-to)147-153
Number of pages7
JournalRadiology
Volume247
Issue number1
DOIs
StatePublished - Apr 2008
Externally publishedYes

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Specific Gravity
Tomography
Kidney
Urine
Urea
Urinary Bladder
Health Insurance Portability and Accountability Act
Ureteral Obstruction
Kidney Pelvis
Urinalysis
Research Ethics Committees
Informed Consent
Linear Models

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

Cite this

Physiology of renal medullary tip hyperattenuation at unenhanced CT : Urinary specific gravity and the NaCl concentration gradient. / Hsu, Christopher T.; Wang, Zhen J.; Yu, Alan S L; Gould, Robert G.; Fu, Yanjun; Joe, Bonnie N.; Qayyum, Aliya; Breiman, Richard S.; Coakley, Fergus; Yeh, Benjamin M.

In: Radiology, Vol. 247, No. 1, 04.2008, p. 147-153.

Research output: Contribution to journalArticle

Hsu, CT, Wang, ZJ, Yu, ASL, Gould, RG, Fu, Y, Joe, BN, Qayyum, A, Breiman, RS, Coakley, F & Yeh, BM 2008, 'Physiology of renal medullary tip hyperattenuation at unenhanced CT: Urinary specific gravity and the NaCl concentration gradient', Radiology, vol. 247, no. 1, pp. 147-153. https://doi.org/10.1148/radiol.2471070585
Hsu, Christopher T. ; Wang, Zhen J. ; Yu, Alan S L ; Gould, Robert G. ; Fu, Yanjun ; Joe, Bonnie N. ; Qayyum, Aliya ; Breiman, Richard S. ; Coakley, Fergus ; Yeh, Benjamin M. / Physiology of renal medullary tip hyperattenuation at unenhanced CT : Urinary specific gravity and the NaCl concentration gradient. In: Radiology. 2008 ; Vol. 247, No. 1. pp. 147-153.
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AU - Wang, Zhen J.

AU - Yu, Alan S L

AU - Gould, Robert G.

AU - Fu, Yanjun

AU - Joe, Bonnie N.

AU - Qayyum, Aliya

AU - Breiman, Richard S.

AU - Coakley, Fergus

AU - Yeh, Benjamin M.

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N2 - Purpose: To retrospectively investigate the physiology of renal medullary tip hyperattenuation at unenhanced computed tomography (CT). Materials and Methods: This retrospective single-institution study was IRB approved and HIPAA compliant. Informed consent was waived. One hundred consecutive patients (53 women, mean age, 52 years; 47 men, mean age, 48 years; P = .39) without and 34 (11 women, mean age, 49 years; 23 men, mean age, 45 years; P = .54) with unilateral ureteral obstruction underwent contemporaneous urinalysis and unenhanced CT. At CT, bladder urine attenuation was measured and two readers recorded the presence of renal medullary tip hyperattenuation. For obstructed kidneys (n = 34), renal pelvic urine attenuation was also recorded. The presence of medullary tip hyperattenuation was correlated with urinary specific gravity. To investigate the physiologic basis of medullary tip hyperattenuation, attenuations for NaCl and urea phantoms (range, 0-2000 mosm/kg) were recorded and correlated to solute concentrations by using linear regression. Results: Patients with renal medullary tip hyperattenuation seen at CT had higher mean urinary specific gravity (1.023 and 1.022 for readers 1 and 2, respectively) than those without (1.015 and 1.016, respectively, both P <.05). The specific gravity correlated with higher urine attenuation (r = 0.40, P <.001). For the 34 patients with unilateral urinary obstruction, medullary tip hyperattenuation was less commonly seen in obstructed (two kidneys each for both readers) than nonobstructed (11 and 15 kidneys, respectively, both P <.005) kidneys and mean urine attenuation was lower in the obstructed renal pelvis (7.4 HU) than in the bladder (11.4 HU) (P <.005). Phantoms showed a 3.6-HU increase per 100-mosm/kg increase in NaCl concentration (r = 0.99, P <.001) but no change in attenuation with different urea concentrations. Conclusion: Renal medullary tip hyperattenuation at unenhanced CT reflects increased urinary specific gravity, likely related to high medullary tip NaCl concentrations.

AB - Purpose: To retrospectively investigate the physiology of renal medullary tip hyperattenuation at unenhanced computed tomography (CT). Materials and Methods: This retrospective single-institution study was IRB approved and HIPAA compliant. Informed consent was waived. One hundred consecutive patients (53 women, mean age, 52 years; 47 men, mean age, 48 years; P = .39) without and 34 (11 women, mean age, 49 years; 23 men, mean age, 45 years; P = .54) with unilateral ureteral obstruction underwent contemporaneous urinalysis and unenhanced CT. At CT, bladder urine attenuation was measured and two readers recorded the presence of renal medullary tip hyperattenuation. For obstructed kidneys (n = 34), renal pelvic urine attenuation was also recorded. The presence of medullary tip hyperattenuation was correlated with urinary specific gravity. To investigate the physiologic basis of medullary tip hyperattenuation, attenuations for NaCl and urea phantoms (range, 0-2000 mosm/kg) were recorded and correlated to solute concentrations by using linear regression. Results: Patients with renal medullary tip hyperattenuation seen at CT had higher mean urinary specific gravity (1.023 and 1.022 for readers 1 and 2, respectively) than those without (1.015 and 1.016, respectively, both P <.05). The specific gravity correlated with higher urine attenuation (r = 0.40, P <.001). For the 34 patients with unilateral urinary obstruction, medullary tip hyperattenuation was less commonly seen in obstructed (two kidneys each for both readers) than nonobstructed (11 and 15 kidneys, respectively, both P <.005) kidneys and mean urine attenuation was lower in the obstructed renal pelvis (7.4 HU) than in the bladder (11.4 HU) (P <.005). Phantoms showed a 3.6-HU increase per 100-mosm/kg increase in NaCl concentration (r = 0.99, P <.001) but no change in attenuation with different urea concentrations. Conclusion: Renal medullary tip hyperattenuation at unenhanced CT reflects increased urinary specific gravity, likely related to high medullary tip NaCl concentrations.

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