CT renal mass (protocol)

The renal mass CT protocol is a multi-phasic contrast-enhanced examination for the assessment of renal masses. It is most often comprised of a non-contrast, nephrogenic phase and excretory phase. However, this article will cover the optional, corticomedullary phase too.

NB: This article is intended to outline some general principles of protocol design. The specifics will vary depending on CT hardware and software, radiologists' and referrers' preference, institutional protocols, patient factors (e.g. allergy) and time constraints. 

Terminology

For some departments and/or radiologists, a renal mass protocol may only include a non-contrast, nephrogenic phase exam. For others, it may consist of a corticomedullary phase (40-60 second delay) and/or an excretory phase (5-10 minute delay).

Indications

Indeterminate renal mass, renal adenocarcinoma, metastasis, monitoring of known renal mass.

Purpose

The purpose of this exam is to assess the location and composition of a renal mass.

• non-contrast scan is best to determine the HU of homogenous renal mass or masses containing macroscopic fat ¹

• corticomedullary phase is best to delineate subcategories of renal cell carcinomas further

• nephrogenic phase is best for optimal enhancement of the renal parenchyma, including the renal medulla, and will demonstrate enhancing components of a mass

• excretory phase will demonstrate enhancement of calyces, renal pelvis and ureters. Many institutions will perform this around 5 minutes to demonstrate opacification of the ureters

Technique (4 phase)

• patient position

  • supine with their arms above their head

• scout 

  • diaphragm to the lesser trochanter

Non-contrast scan

• scan extent

  • ​mid-diaphragm to the iliac crest (covering kidneys)

• scan direction

  • craniocaudal

• scan delay

  • none

• ​respiration phase

  • ​inspiration, breath-hold

Corticomedullary phase

• scan extent

  • ​​mid-diaphragm to the iliac crest (covering kidneys)

• scan direction

  • craniocaudal

• contrast injection considerations (bolus tracking)

  • monitoring slice (region of interest)

    • level of the diaphragmatic hiatus or first lumbar vertebra at the aorta

• threshold

  • 150 HU

• volume

  • 100 mL of non-ionic contrast at 3 to 5 mL/s (a higher flow rate will equal greater enhancement) 

• scan delay ²

  • corticomedullary 

    • 20-30 seconds post bolus trigger (30-40 s after injection)

• ​respiration phase

  • ​inspiration, breath-hold

Nephrogenic phase

• scan extent​

  • mid-diagram-diaphragm to lesser trochanter (covering entire renal system)

• scan direction

  • craniocaudal

• contrast injection considerations

• scan delay

  • nephrographic phase

    • 100 seconds post-injection

• ​respiration phase

  • ​inspiration, breath-hold

Excretory phase

• scan extent​

  • mid-diagram-diaphragm to lesser trochanter (covering entire renal system)

• scan direction

  • craniocaudal

• contrast injection considerations

• scan delay

  • excretory phase

    • 5-10 minutes post-injection 

• ​respiration phase

  • ​inspiration, breath-hold

Practical points

• pseudoenhancement, an artifact encountered where the calculated density of a lesion is inaccurately increased, is a problem often noted in renal mass scans,  dual-energy CT via virtual monoenergetic images at a KeV range of 80 Kev to 90 KeV can minimise beam hardening and partial voluming and overcome this issue