Editing Kidney Cancer: Diagnosis and Evaluation (section)

=== Modalities ===

==== Options ====
# '''<span style="color:#ff0000">Ultrasound</span>'''
# '''<span style="color:#ff0000">CT</span>'''
# '''<span style="color:#ff0000">MRI</span>'''
# '''Other'''
## '''Contrast-enhanced US'''
## '''PET-CT'''
*'''None of the current imaging modalities can reliably distinguish between benign and malignant tumors or between indolent and aggressive tumor biology'''

==== US ====
* Strict US criteria for a simple cyst (3):
*# Smooth cyst wall
*# Round or oval shape '''without internal echoes'''
*# Through-transmission with strong acoustic shadows posteriorly
* '''Acute focal pyelonephritis (lobar nephronia) is hypoechoic'''
* '''Angiomyolipomas are usually echogenic'''
* '''RCCs and intrarenal abscesses have variable echogenicity'''
* '''Angiomyolipomas demonstrate a speed-propagation artifact'''
** Speed of sound in the fat is significantly slower than that in the soft tissue, due to the presence of fat in the tumor
* '''A renal mass that is not clearly a simple cyst by strict US criteria should be evaluated further with CT'''

==== 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
|}

==== MRI ====
* '''Alternate standard to CT'''
** '''Similar sensitivity and specificity to CT'''
***Sensitivity: 88% (interquartile range [IQR] 81%-94%) CT vs. 87.5% (IQR 75.25%-100%) MRI
***Specificity: 75% (IQR 51%-90%) CT vs. 89% (IQR 75%-96%) MRI
***[https://pubmed.ncbi.nlm.nih.gov/30528378/ Vogel, Christina, et al.] "Imaging in suspected renal-cell carcinoma: systematic review." ''Clinical genitourinary cancer'' 17.2 (2019): e345-e355.
**Considered comparable to CT in characterizing indeterminate renal masses by the American College of Radiology[https://pubmed.ncbi.nlm.nih.gov/33153554/]
**CT may be better for smaller lesions
**'''Most useful in patients in whom contrast is contraindicated because of severe allergy or severe CKD'''
** '''Gadolinium contrast can be given to patients with GFR < 30 mL/min/1.73m2[https://pubmed.ncbi.nlm.nih.gov/33170103/]'''
** '''Nephrogenic systemic fibrosis (NSF)'''
*** Fibrosing dermopathy associated with soft tissue deposition and accumulation of gadolinium
*** '''Potentially serious complication of gadolinium contrast'''
*** '''Very rare'''
**** '''More common with group I gadolinium based contrast agents'''
***** Incidence <0.07% in patients with CKD 4 and 5 with group II agents
***** Group II gadolinium based contrast agents are considered safe for any level of eGFR
****** '''Renal function does not need be screened prior to receiving group II gadolinium based contrast agents'''
*** '''Prevention in patients with ESRD: perform hemodialysis after the MRI scan.'''
* '''Image Sequences'''
**Lesions in upper pole and lower pole may be skipped when scrolling through axial slices, always look at coronal images
**T2WI
***Most useful for anatomic assessment of renal masses
***Usually two T2 sequences, one with fat suppression and one without
***Renal vessels will be dark
**Diffusion weighted imaging
***Sequences with higher b-value more likely useful
*'''Enhancement > 20% is suspicious for RCC'''
* '''For a fat-containing tumor, a T2-weighted image with fat suppression is most likely to identify macroscopic fat and confirm the diagnosis of an angiomyolipoma (AML).'''
* '''Best study for evaluation of invasion into adjacent structures'''
** '''Large tumours may indent and compress adjacent liver parenchyma but seldom actually grow by direct extension into the liver; obliteration of the fat plane between the tumour and adjacent organs (e.g. the liver) on CT can be a misleading finding and should prompt further imaging with MRI'''. In reality, surgical exploration is often required to make an absolute differentiation.

==== Contrast-enhanced US using microbubbles ====
* '''May play an important role in the future for characterizing renal masses''' '''in select patients in whom other forms of intravenous contrast are contraindicated.'''

==== RENAL nephrometery score ====
* '''Based on the 5 most reproducible features that characterize the anatomy of a solid renal mass'''
*# '''(R)adius''' (maximal tumor size)
*# '''(E)xophytic/endophytic'''
*# '''(N)earness of the deepest portion of the tumor to the collecting system or renal sinus'''
*# '''(A)nterior (a)/posterior (p)''' descriptor
*# '''(L)ocation relative to the polar line'''
** All components except for the (A) descriptor are scored on a 1, 2, or 3-point scale.
* '''Range 4-12, lower number more amenable to partial nephrectomy:'''
** More [https://pubmed.ncbi.nlm.nih.gov/19616235/ details] on RENAL nephrometery score