Editing Benign Kidney Tumours (section)

=== Diagnosis and Evaluation ===

==== History and physical exam ====
* '''Usually asymptomatic'''
* Rarely, benign cystic lesions can cause pain and/or hypertension
* Symptoms can occur as a consequence of hemorrhage within the cyst or spontaneous or traumatic cyst rupture

==== Imaging ====
* '''<span style="color:#ff0000">Any renal lesion that is not a simple cyst should be further characterized with contrast-enhanced axial imaging to better characterize the cyst</span>'''

===== Bosniak classification of renal cysts =====
* '''Originally devised using CT scans'''
** Can be used in MRI, but '''MRI tends to exaggerate some findings related to cysts'''

{| class="wikitable"
|'''<span style="color:#ff0000">Bosniak category</span>'''
|'''<span style="color:#ff0000">Key features</span>'''
|'''<span style="color:#ff0000">Risk of malignancy</span>'''

'''<span style="color:#0000ff">(5-15-55-90)</span>'''
|'''CT Appearance'''
|-
|'''<span style="color:#ff0000">I (simple cyst)</span>'''
|
* '''Usually round or oval shape'''
* '''Anechoic with posterior enhancement on US'''
* '''Regular contour with clear interface with renal parenchyma'''
* '''<span style="color:#ff0000">No septa, calcification or enhancement</span>'''
| 
|
|-
|'''<span style="color:#ff0000">II</span>'''
|
* '''<span style="color:#ff0000">Single thin septum (<1 mm)</span>'''
* '''<span style="color:#ff0000">Fine calcification (often small, linear, parietal, or septal)</span>'''
* '''<span style="color:#ff0000">No perceived contrast enhancement</span>'''
* '''<span style="color:#ff0000">Hypderdense cyst <3 cm; >20 HU</span>'''
|'''<span style="color:#ff0000">5%</span>'''

Likely gross overestimation of the true risk, as most of the malignant category II lesions had features that made them too complex to be considered a true category II cyst
|
|-
|'''<span style="color:#ff0000">IIF</span>'''
|
* '''Cyst unequivocally categorized as category II or III cysts'''
* '''<span style="color:#ff0000">Multiple thin septae or a slightly thickened, but smooth septa</span>'''
* '''<span style="color:#ff0000">Calcifications – thick or nodular</span>'''
* '''<span style="color:#ff0000">No perceived contrast enhancement</span>'''
* '''<span style="color:#ff0000">Hyperdense cysts ≥3 cm</span>'''
|'''<span style="color:#ff0000">8-27%</span>'''
|
|-
|'''<span style="color:#ff0000">III</span>'''
|
* '''Uniform wall thickening and/or nodularity'''
* '''Irregular, thickened, and/or calcified septa'''
* '''<span style="color:#ff0000">Contrast-enhancing septa</span>'''
|'''<span style="color:#ff0000">54%</span>'''
|
|-
|'''<span style="color:#ff0000">IV</span>'''
|
* '''Wall-thickening'''
* '''Gross, irregular, and nodular septal thickening</span>'''
* '''<span style="color:#ff0000">Solid contrast-enhancing component, independent of septa</span>'''
|'''<span style="color:#ff0000">88%</span>'''
|
|}

* '''[https://pubs.rsna.org/doi/10.1148/radiol.2019182646 Proposed updated 2019 classification]'''
* [https://radiopaedia.org/articles/bosniak-classification-system-of-renal-cystic-masses Radiopaedia article] on Bosniak classification of renal cysts

==== Other ====
* '''Renal tumour biopsy (RTB)'''
** Significantly less informative for the diagnosis of cystic lesions compared to solid lesions
** '''Generally, not diagnostic for most Bosniak III cysts, as there is minimal targetable solid component'''
** '''For Bosniak IV cysts, a biopsy of the solid component may be considered to confirm the presence of a malignant tumour and to help with decision-making in select cases (elderly, multiple comorbidities, unfit for treatment, etc)'''