Editing Benign Kidney Tumours (section)

== Renal Cysts ==

* '''Most common benign renal lesion'''
* Increase in size and number over time

=== Pathogenesis ===
* '''Develop within renal tubules''' by pathogenetic processes that involve cellular proliferation, accumulation of tubule fluid within distended cavities, and remodeling of extracellular matrix§
* '''<span style="color:#ff0000">Risk factors for renal cysts (4):</span>'''
*# '''<span style="color:#ff0000">Increasing age</span>'''
*# '''<span style="color:#ff0000">Male gender</span>'''
*# '''<span style="color:#ff0000">Hypertension</span>'''
*# '''<span style="color:#ff0000">Renal insufficiency</span>'''
* '''In patients with autosomal-dominant polycystic kidney disease (ADPKD), cyst formation is due to loss of PKD1 (polycystin-1 protein) or PKD2 (polycystin-2)'''
* '''Acquired renal cystic disease is associated with increased risk of RCC'''

=== 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)'''

=== Management ===
* '''<span style="color:#ff0000">Based on Bosniak classification</span>[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5365391/]'''
** '''<span style="color:#ff0000">Bosniak I and II</span>'''
*** '''<span style="color:#ff0000">Follow-up not warranted</span>'''
**** '''Majority will grow over time'''; growth should not necessarily be considered a sign a malignancy
**** Transformation into a more complex cyst is rare
*** '''<span style="color:#ff0000">Intervention only warranted if the cyst becomes symptomatic</span>''' (bleeding, recurrent infection or pain)
**** '''Treatment options:'''
****# '''Percutaneous management (aspiration +/- sclerotherapy)'''
****# '''Cyst decortication'''
****# '''Surgical resection'''
**** Percutaneous cyst decompression may be considered prior to offering definitive treatment as a means to confirm that the source of symptoms are cyst-related
** '''<span style="color:#ff0000">Bosniak IIF</span>'''
*** '''≈15% of these category IIF cysts will progress in complexity''' (to Bosniak category III or IV)
*** '''<span style="color:#ff0000">Should be followed with imaging</span>'''
**** '''<span style="color:#ff0000">Contrast-enhanced CT scan or MRI (not US) every 6 months for the first year. Cases without progression should be followed annually for at least 5 years</span>'''
** '''<span style="color:#ff0000">Bosniak III/IV</span>'''
*** '''<span style="color:#ff0000">Surgical excision is generally suggested</span>'''
*** '''<span style="color:#ff0000">Bosniak III</span>'''
**** '''Given the low metastatic potential of cystic RCC, the panel feels that reduced surgical margins and controlled cyst decompression (if required) can be performed with low risk of tumour recurrence'''
**** '''For the same reason, active surveillance and thermal-ablation therapies (see below) may also be considered as appropriate treatment alternatives in select cases'''
*** '''<span style="color:#ff0000">Bosniak IV</span>'''
**** '''Most of these malignant cysts are thought to have low metastatic potential and thus, more conservative management may be safely considered in select cases'''
*** '''<span style="color:#ff0000">2017 AUA Localized RCC Guideline:</span>'''
**** '''<span style="color:#ff0000">AS is an option as initial management, especially those <2cm</span>'''
**** '''AS/expectant management should be prioritized when the anticipated risk of intervention or competing risks of death outweigh the potential oncologic benefits of active treatment'''
**** For patients in whom the
***** Risk/benefit analysis for treatment is equivocal and who prefer AS, physicians should repeat imaging in 3-6 months to assess for interval growth and may consider RMB for additional risk stratification.
***** Anticipated oncologic benefits of intervention outweigh the risks of treatment and competing risks of death, physicians should recommend active treatment. In this setting, AS with potential for delayed intervention may be pursued only if the patient understands and is willing to accept the associated oncologic risk.

* '''Role of active surveillance for suspected cystic RCC'''
** '''The vast majority of cystic RCCs are multilocular cystic RCCs (mcRCC)''' though all RCC subtypes may present in a predominantly cystic form
*** '''Cystic RCCs need to be distinguished from solid renal masses with necrotic components, which behave more aggressively'''
** '''<span style="color:#ff0000">mcRCCs have low malignant potential</span>'''
*** '''Better cancer-specific and overall survival compared with solid RCCs'''
**** '''There has yet to be a report demonstrating metastases or recurrence of mcRCCs.'''
**** One potential explanation for this indolent behaviour is that the majority of mcRCCs tumour volume is fluid and therefore the actual tumour burden is much lower when compared to similar sized solid tumours.
*** To reflect this indolent behaviour, the International Society of Urological Pathology (ISUP) now recommends calling these lesions multilocular cystic renal neoplasm with low malignant potential
*** As the outcomes of these tumours do not seem to be influenced by the overall lesion size, some have even suggested to abandon the current pathological T staging for mcRCC and to reassigned them a new stage called pT1c (c for cystic).
** '''Given their relatively indolent behaviour, there is emerging evidence suggesting that these lesions (especially Bosniak classification III) can be safely managed by active surveillance'''
*** If active surveillance is considered, consider abdominal imaging every 6 months for the first 2 years, followed by yearly imaging thereafter, if the lesion is stable.
** '''<span style="color:#ff0000">Triggers for intervention on active surveillance for suspected cystic RCC are yet to be clearly defined and validated, but may include (3):</span>'''
**# '''<span style="color:#ff0000">Progression from Bosniak III to IV</span>'''
**# '''<span style="color:#ff0000">Growth of solid nodule > 3 cm</span>'''
**# '''<span style="color:#ff0000">Fast-growing nodule</span>'''
* '''Thermal-ablation therapies (RFA, cryotherapy)'''
** '''Given the limited data, RFA should be limited to patients with small Bosniak category III and IV cysts who are poor operative candidates and in whom active surveillance is not being considered'''
** '''The role of cryotherapy in the management of Bosniak III or IV cysts is not well-defined,''' only a few cases reports in the literature