Editing Kidney Cancer: Diagnosis and Evaluation (section)

==== CT ====

* '''Contrast-enhanced CT is the modality of choice in evaluating cystic renal masses.[https://pubmed.ncbi.nlm.nih.gov/31900669/]'''
**'''MRI is used when CT is contraindicated''' (e.g., patients with allergy to iodinated contrast agent) or as a problem-solving modality for equivocal findings. MRI can show some septa that are less apparent at CT and demonstrate definitive enhancement in those cysts that show only equivocal enhancement at CT. As a consequence, renal cysts can be placed in a higher Bosniak category with MRI than with CT'''[https://pubmed.ncbi.nlm.nih.gov/31900669/]'''

===== IV contrast =====

*'''<span style="color:#ff0000">Contraindications (2):'''
*# '''<span style="color:#ff0000">Severe allergy'''
*# '''<span style="color:#ff0000">Severe chronic kidney disease'''
** '''<span style="color:#ff0000">Patients with GFR <45 ml/min/1.73m2 should receive contrast with caution</span>'''
*** '''Patients with acute kidney injury or GFR < 30 mL/min/1.73m2 who are not undergoing renal replacement therapy should receive intravenous normal saline prophylaxis prior to receiving iodinated contrast media[https://pubmed.ncbi.nlm.nih.gov/34115547/ §].'''
*** '''Patients with GFR 30-44 mL/min/1.73m2 may be considered for intravenous fluid prophylaxis per individual physician discretion based on the patient’s risk factor for renal injury[https://pubmed.ncbi.nlm.nih.gov/34115547/ §].'''
**** '''MRI with second generation gadolinium-based intravenous contrast is now a safer option in many patients with severe CKD'''
**'''In patients who cannot receive intravenous contrast, MRI, non-contrast CT, and US (with Doppler) can be used to characterize renal masses''' 
*'''<span style="color:#ff0000">Contrast-induced nephropathy'''
** '''Due to intrarenal vasoconstriction and tubular necrosis'''
** '''<span style="color:#ff0000">Risk factors'''
**# '''<span style="color:#ff0000">Diabetes mellitus'''
**# '''<span style="color:#ff0000">Advanced age'''
**# '''<span style="color:#ff0000">Congestive heart failure'''
**# '''<span style="color:#ff0000">Hypertension'''
**# '''<span style="color:#ff0000">Dehydration'''
**# '''<span style="color:#ff0000">Diuretic use'''
**# '''<span style="color:#ff0000">Low hematocrit'''
**# '''<span style="color:#ff0000">Ventricular ejection fraction < 40%'''
**# '''<span style="color:#ff0000">Concomitant exposure to chemotherapy, aminoglycoside or nonsteroidal anti-inflammatory agents'''
**# '''<span style="color:#ff0000">Hyperuricemia'''
**# '''Diseases that affect renal hemodynamics, such as end-stage liver disease and nephrotic syndrome'''
**# '''Patients with a diagnosis of a paraproteinemia syndrome/disease (e.g., multiple myeloma), history of a kidney transplant, renal tumor, renal surgery, or single kidney may also be at higher risk'''
*** '''The patients at highest risk for developing CIN are those with both diabetes and pre-existing renal insufficiency.'''
** '''<span style="color:#ff0000">Metformin'''
*** '''Patients with type 2 diabetes mellitus receiving metformin may have an accumulation of the drug after administering intravascular radiologic contrast medium (IRCM), resulting in biguanide lactic acidosis'''
*** '''Biguanide lactic acidosis'''
**** Symptoms of include vomiting, diarrhea, and somnolence
**** Fatal in ≈50% of cases
**** '''Rare in patients with normal renal function (no defined threshold but some studies suggest <60).'''
***** '''In patients with normal renal function and no known comorbidities there is no need to discontinue metformin before IRCM use, nor is there a need to check creatinine following the imaging study.'''
***** '''<span style="color:#ff0000">In patients with renal insufficiency metformin should be discontinued the day of the study and withheld for 48 hours. Post-procedure creatinine should be measured at 48 hours and metformin started once kidney function is normal.'''
**** It is not necessary to discontinue metformin before gadolinium-enhanced MRI studies when the amount of gadolinium administered is in the usual dosage range of 0.1 to 0.3 mmol per kilogram of body weight.
*** Prevention of CIN is of great concern and has been a subject of many different studies. Hydration is the major preventative action against CIN. Periprocedural IV hydration with 0.9% saline at 100 mL/hr 12 hours before to 12 hours after has been shown to decrease the incidence of CIN after IV contrast use

===== Findings =====

*'''<span style="color:#ff0000">Enhancement'''
** <span style="color:#ff0000">'''Hounsfield units (HU) are a standardized quantitative measurement of x-ray attenuation'''</span>[https://pubmed.ncbi.nlm.nih.gov/29362150/]
**'''If homogenous lesion and HU on non-contrast CT is[https://pubmed.ncbi.nlm.nih.gov/29362150/]'''
***'''<span style="color:#ff0000"><20, then simple cyst'''
***'''>70, then hemorrhagic/proteinaceous cysts'''
***'''20-70, then considered indeterminate and warrants further evaluation'''
**'''<span style="color:#ff0000">On contrast-enhanced CT, if change in HU (compared to non-contrast)</span>[https://pubmed.ncbi.nlm.nih.gov/29362150/]'''
***'''<span style="color:#ff0000">>20, then considered enhancing</span>'''
***'''<10, then no enhancement'''
***'''10-20, then indeterminate enhancement'''
**'''<span style="color:#ff0000">Differential diagnosis of an enhancing renal mass on CT scan[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5258153/]</span>'''
***'''<span style="color:#ff0000">Hyperdense cyst</span>'''
****'''Hyperdense cysts are benign lesions that contain old, degenerated, or clotted blood and have increased CT attenuation (>20 HU)'''
***'''<span style="color:#ff0000">Renal cell carcinoma</span>'''
****'''<span style="color:#ff0000">Any solid renal mass that enhances >15 Hounsfield units and does not exhibit fat density should be considered a renal cell carcinoma (RCC) until proven otherwise</span>'''
***** '''Clear cell enhances more than papillary and chromophobe RCC'''
****** Emerging data suggests that clear cell RCC may be distinguished from the papillary subtype (papillary RCC is often hypo-enhancing). However, both malignant and benign masses can display heterogeneous avid contrast enhancement patterns and no definitive conclusion can be drawn regarding biological potential based on enhancement pattern alone
** '''<span style="color:#ff0000">Solid masses that have substantial areas of negative CT attenuation (<-20 HU) indicative of fat are diagnostic of AML'''
*** '''≈5-10% of AML’s are fat poor'''
*** '''In rare instances RCC may demonstrate fat''' density on imaging and even pathologically, '''but this is the exception rather than the rule'''
* '''Tumors with calcification associated with fat are uncommon but are almost always malignant RCC.'''
** In this setting the fat is thought to be a reactive process related to tumor necrosis.
** Calcification is virtually never seen in association with AML.
*'''Lymphadenopathy'''
** '''Enlarged hilar or retroperitoneal lymph nodes (≥2 cm) on CT almost always harbor malignancy, but this should be confirmed by surgical exploration or percutaneous biopsy if the patient is not a surgical candidate.'''
** '''Many smaller nodes prove to be inflammatory rather than neoplastic and should not preclude surgical therapy'''

*
{| class="wikitable"
|+Left, endophytic, renal mass on contrast-enhanced CT scan in a 45-year old male. Radical nephrectomy pathology demonstrated pT2a, clear cell renal cell carcinoma
![[File:Kidney CT Mass Axial.png|frameless|592x592px]]
![[File:Kidney CT Mass Sagittal.png|none|thumb|655x655px]]
|-
|Axial view
|Sagittal view
|}