Editing Benign Kidney Tumours (section)

== Angiomyolipoma ==

=== Epidemiology ===
* '''Sex'''
** '''Predominantly found in females'''
*** Strongly expresses estrogen receptor β, progesterone receptor, and androgen receptor suggesting '''a potential hormonal influence'''
* '''Age'''
** '''Rare before puberty'''
** Decreased incidence of sporadic AMLs with increased age
* '''Most often sporadic but can also be associated with autosomal dominant tuberous sclerosis complex (TSC)'''
** '''20-30% of AMLs occur in patients with TSC'''
** '''50% of patients with TSC develop AMLs'''
** '''See Kidney Cancer Pathology and Familial Syndromes Chapter Notes for further details on TSC'''

=== Pathology ===
* '''Thick-walled poorly organized <span style="color:#ff0000">blood vessels, smooth muscle, and varying levels of mature adipose tissue</span>'''
* '''<span style="color:#ff0000">Benign lesion,</span> but can have extra-renal occurrences''' '''indicating multicentric origin rather than malignancy with metastasis'''
** '''<span style="color:#ff0000">Malignant epithelioid variant can metastasize and cause death</span>'''
* '''<span style="color:#ff0000">Positive immunoreactivity for HMB-45 (human melanoma black 45) is characteristic for AML</span>'''

=== Diagnosis and Evaluation ===

==== History and Physical Exam ====

*'''Clinical Presentation'''
** '''<span style="color:#ff0000">Spontaneous perirenal hemorrhage</span>'''
*** '''<span style="color:#ff0000">Renal neoplasm most commonly associated with spontaneous perirenal hemorrhage, closely followed by RCC</span>'''
*** Aneurysmal dilation is found in 50% of AMLs; size of aneurysm correlates with risk of rupture
*** '''Wunderlich syndrome, which is a massive spontaneous non-traumatic retroperitoneal hemorrhage (from any cause), is the most significant complication of AML'''
*** '''<span style="color:#ff0000">Pregnancy increases risk of AML hemorrhage</span>'''

==== Imaging ====
* '''<span style="color:#ff0000">The only benign renal tumour that is confidently diagnosed on imaging</span>'''
** '''<span style="color:#ff0000">Presence of fat (≤-20 HFU) within a renal lesion is considered a diagnostic landmark</span>'''
*** '''<span style="color:#ff0000">Other lesions that can contain fat (2):</span>'''
**** '''<span style="color:#ff0000">Liposarcoma</span>'''
***** '''Should be considered in the differential of a fat-containing retroperitoneal tumour'''
*****Can distinguish from RCC by whether mass originates from kidney or retroperitoneum, the latter of which may displace kidney
**** '''<span style="color:#ff0000">Fat-containing RCC</span>'''
***** '''In RCC, the fat is thought to be a reactive process related to tumor necrosis.'''
*** '''<span style="color:#ff0000">≈5% of AML’s are fat poor</span>'''
**** '''<span style="color:#ff0000">Fat-poor AML can be difficult to distinguish from RCC</span>'''
**** '''<span style="color:#ff0000">Calcification is virtually never seen in association with AML</span>'''
***** '''<span style="color:#ff0000">Clinical implication: presence of fat with calcification is suggestive of RCC</span>'''
** '''MRI can be used in difficult cases when the lesion has minimal fat'''
***'''A T2-weighted image with fat suppression is most likely to identify macroscopic fat and confirm the diagnosis of an angiomyolipoma (AML).'''

==== Other ====
* '''Biopsy'''
** '''Consider biopsy if imaging findings equivocal'''

=== Management ===
* '''Consider size of the tumour, presence of symptoms, and patient factors'''
** Most studies have focused on a 4-cm cut point but size represents a continuum of risk
* '''<span style="color:#ff0000">Asymptomatic, smaller tumors (typically <4 cm)</span>'''
** '''<span style="color:#ff0000">Observation (preferred) with repeat initial imaging at 6 to 12 months to define the growth rate and clinical significance.</span>'''
*** Repeat imaging can be lengthened once stability has been established, with follow-up performed only annually or biannually for smaller tumors
*** Solitary, sporadic AMLs have a mean growth rate of 5%/year; multifocal AMLs and those in patients with TSC have mean growth rate of 20%/year
* '''<span style="color:#ff0000">Symptomatic or larger tumors (>4cm)</span>'''
** '''<span style="color:#ff0000">Consider intervention taking into account the patient’s age, comorbidities, and other related factors</span>'''
*** '''<span style="color:#ff0000">A proactive approach should also be considered In (2):</span>'''
***# '''<span style="color:#ff0000">Females of childbearing age</span>'''
***# '''<span style="color:#ff0000">Patients with limited access to surveillance or to emergency care</span>'''
* '''<span style="color:#ff0000">Options for intervention (4):'''
*# '''<span style="color:#ff0000">Partial nephrectomy'''
*# '''<span style="color:#ff0000">Selective embolization'''
*#* '''Disadvantages'''
*#**'''Many require repeat procedures'''
*#**'''Risk of complications from procedure'''
*#*** Overall complication rate with embolization in some series is 10%, similar to rates of partial nephrectomy
*#**** Potential complications of embolization include hemorrhage, abscess formation, or sterile liquefaction of the tumor requiring percutaneous drainage or surgical intervention.
*#**'''Extended follow-up after selective embolization is needed, which would not be required after partial nephrectomy'''
*# '''<span style="color:#ff0000">Thermal ablation'''
*#* Limited data on efficacy
*#** Follow-up remains short, the evaluation of success remains poorly defined, and the duration for continued radiographic surveillance is unknown, thus committing the patient to multiple, long-term imaging
*# '''<span style="color:#ff0000">Sirolimus'''
*#* Has been investigated and can be used to reduce size of AML for possible surgery later