Imaging Pearls ❯ Kidney ❯ Renal Angiomyolipoma
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- “Similar to LAM, AMLs are mesenchymal tumors categorized under the PEComa family of neoplasms. These tumors originate from clonal proliferation of epithelioid cells located around blood vessels. AMLs may be found in multiple organs, most notably the kidneys, and the presence of two or more of these tumors is considered a major feature of TSC. Renal AMLs can be identified in 55%–75% of patients with TSC. They are often discovered incidentally owing to their asymptomatic nature; however, they can manifest with abdominal pain, hematuria, anemia, hypertension, and/or retroperitoneal hemorrhage. Renal AMLs can multiply and grow during puberty, suggesting an estrogenic influence.”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010 - “There are two histologic subtypes of AML: classic and epithelioid. At gross pathologic examination, classic AML appears as a well-defined expansile mass in the renal cortex or medulla. Tortuous vasculature, clear to eosinophilic cells, and spindle cells are visible at microscopy. Epithelioid AMLs occur more frequently in patients with TSC (27%) than in the general population (7%). Malignant transformation of epithelioid AMLs can occur and may be suspected in the presence of rapid growth or necrosis. In contrast, classic AMLs tend to remain benign.”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010 - “The hallmark finding of lipid-rich AML is the presence of intratumoral fat with an attenuation of −10 HU or lower on noncontrast CT images. These tumors demonstrate variable enhancement. It should be noted that RCC may rarely demonstrate a small amount of intratumoral fat, and this is a potential cause of diagnostic dilemmas. The presence of calcification within a fat-containing renal mass should alert the clinician to the diagnosis of RCC. In contrast, calcification is extremely rare in AML.”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010 - “Renal AMLs represent the second most frequent cause of morbidity among patients with TSC owing to the risk of spontaneous hemorrhage and rupture. Such complications occur increasingly with AMLs that are larger than 4 cm or those that are associated with aneurysms larger than 5 mm. If either of these criteria is met, embolization or nephron sparing surgery is highly recommended. Tumors that do not fulfill this criterion are followed up conservatively or treated with mTOR inhibitors, elective embolization, ablative therapies, or nephron-sparing surgery.”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010 - “Renal cysts are the second most prevalent renal feature of TSC, occurring in 17%–47% of pediatric patients with TSC. Because of their low specificity, multiple renal cysts are considered a minor feature of TSC. TSC-related renal cysts can appear with varying severity, from microscopic disease to a serious polycystic variation. The polycystic variation occurs in about 2%–3% of patients with TSC and results from contiguous mutations of TSC2 and polycystic kidney disease type 1 (PKD1) genes, which are located close to each other on chromosome 16p13.3.”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010 - “RCC occurs in only 2%–3% of persons with TSC, similar to its prevalence in the general population. However, unlike sporadic RCC, TSC-related RCC occurs in comparatively young individuals—in whom the median age at diagnosis is 28 years—and tends to be less aggressive . TSC-related RCC can be categorized into three major histologic subtypes: papillary, chromophobe, and clear cell. These subtypes tend to exhibit different imaging patterns owing to their varying histologic components..”
Tuberous Sclerosis: Current Update
Wang MX et al.
RadioGraphics 2021; 41:1992–2010
- “Lymphangioleiomyomatosis (LAM) is a rare idiopathic disease that exclusively occurs in women of childbearing age, and this disease is characterized by the proliferation of abnormal smooth muscle cells in the lungs and along the thoracic and abdominal lymphatics. The disease primarily affects the lungs in the majority of cases, but extrapulmonary LAM occasionally occurs with or without subsequent involvement of the lungs.”
CT and MR imaging findings of lymphangioleiomyomatosis involving the uterus and pelvic cavity.
Kim YS, Rha SE, Byun JY, Lee A, Park JS
Korean J Radiol. 2011;12(2):261‐265. doi:10.3348/kjr.2011.12.2.261 - “LAM occurs in about 30% of the women with tuberous sclerosis complex (TSC), which is an autosomal dominant multisystem neurocutaneous disorder of highly variable penetrance, and it is characterized by hamartomas, seizure and mental retardation.”
CT and MR imaging findings of lymphangioleiomyomatosis involving the uterus and pelvic cavity.
Kim YS, Rha SE, Byun JY, Lee A, Park JS
Korean J Radiol. 2011;12(2):261‐265. doi:10.3348/kjr.2011.12.2.261 - Lymphangioleiomyomatosis: Abdominal Findings
- renal angiomyolipomas: most common abdominal finding
- splenic cysts
- chylous ascites
- lymphangioleiomyomas
- uterine fibroids
- abdominal lymphadenopathy - Lymphangioleiomyomatosis: Facts
- characteristic or compatible lung HRCT and lung biopsy fitting the pathological criteria for LAM or
- characteristic lung HRCT and any of the following
--- renal angiomyolipoma
--- thoracic or abdominal chylous effusion
--- lymphangioleiomyoma or lymph-node involved by LAM
--- definite or probable tuberous sclerosis
- “Lymphangioleiomyomatosis (LAM) is a rare idiopathic disease that exclusively occurs in women of childbearing age, and this disease is characterized by the proliferation of abnormal smooth muscle cells in the lungs and along the thoracic and abdominal lymphatics. The disease primarily affects the lungs in the majority of cases, but extrapulmonary LAM occasionally occurs with or without subsequent involvement of the lungs.”
CT and MR imaging findings of lymphangioleiomyomatosis involving the uterus and pelvic cavity.
Kim YS, Rha SE, Byun JY, Lee A, Park JS
Korean J Radiol. 2011;12(2):261‐265. doi:10.3348/kjr.2011.12.2.261 - “LAM occurs in about 30% of the women with tuberous sclerosis complex (TSC), which is an autosomal dominant multisystem neurocutaneous disorder of highly variable penetrance, and it is characterized by hamartomas, seizure and mental retardation.”
CT and MR imaging findings of lymphangioleiomyomatosis involving the uterus and pelvic cavity.
Kim YS, Rha SE, Byun JY, Lee A, Park JS
Korean J Radiol. 2011;12(2):261‐265. doi:10.3348/kjr.2011.12.2.261 - Lymphangioleiomyomatosis: Abdominal Findings
- renal angiomyolipomas: most common abdominal finding
- splenic cysts
- chylous ascites
- lymphangioleiomyomas
- uterine fibroids
- abdominal lymphadenopathy - Lymphangioleiomyomatosis: Facts
- characteristic or compatible lung HRCT and lung biopsy fitting the pathological criteria for LAM or
- characteristic lung HRCT and any of the following
--- renal angiomyolipoma
--- thoracic or abdominal chylous effusion
--- lymphangioleiomyoma or lymph-node involved by LAM
--- definite or probable tuberous sclerosis
- OBJECTIVE. Three-dimensional printing is being used for surgical assistance, particularly for robot-assisted partial nephrectomy (RAPN). The objective of this study was to assess the anatomic accuracy of the 3D model used for 3D model–guided RAPN.
CONCLUSION. Three-dimensional printed models are accurate with respect to anatomic reality. The reliability of surgical assistance with 3D printed models must be evaluated.
Measurement of the Accuracy of 3D-Printed Medical Models to Be Used for Robot-Assisted Partial Nephrectomy
Michiels C et al.
AJR 2019; 213:1–6 - “Our 3D models are accurate with respect to the anatomic reality of the different measurements and arterial distribution. These 3D models allow use of a clampless technique or segmental renal artery clamping to minimize renal ischemia and to preserve postoperative renal function. The reliability of surgical assistance with 3D printing must be prospectively evaluated.”
Measurement of the Accuracy of 3D-Printed Medical Models to Be Used for Robot-Assisted Partial Nephrectomy
Michiels C et al.
AJR 2019; 213:1–6 - Three-dimensional printing is appreciated because surgeons can have a tac- tile experience with the renal tumor and re- nal system and thus determine better surgical plans and treatment strategies. Marconi et al. found that 3D printed models assisted medical students, surgeons, and radiologists in identifying anatomic structures.”
Measurement of the Accuracy of 3D-Printed Medical Models to Be Used for Robot-Assisted Partial Nephrectomy
Michiels C et al.
AJR 2019; 213:1–6
- OBJECTIVE. The purpose of this article is to describe useful imaging features for differentiating angiomyolipoma (AML) subtypes from renal cell carcinoma subtypes.
CONCLUSION. A newer radiologic classification of renal AML consists of fat-rich AML (≤ –10 HU), fat-poor AML (> –10 HU; tumor-to-spleen ratio < 0.71; signal intensity index, > 16.5%), and fat-invisible AML (> –10 HU; tumor-to-spleen ratio, > 0.71; signal intensity index, < 16.5%). Each subtype must be differentiated from the renal cell carcinoma subtype because of overlapping imaging features.
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - “Song et al. [1] reported on a new radiologic classification of renal angiomyolipoma (AML) in which they classified the tumor into three subtypes: fat-rich AML, fat-poor AML, and fat-invisible AML. Each AML subtype is defined according to the amount of fat, which is quantified with CT or MRI. Fat-rich AML measures –10 HU or less at CT. Both fat-poor AML and fat-invisible AML measure more than –10 HU.”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - Fat-rich AML is defined as a lesion mea- suring –10 HU or less on unenhanced CT images .This subtype constitutes approximately 95% of renal AMLs. Almost all fat-rich AMLs are easily diagnosed with unenhanced CT alone because fat, a hallmark of AML, is clearly visualized.”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - “Approximately 5% of renal AMLs histo- logically have a small amount of fat and correspond to fat-poor AML or fat-invisible AML in the Song classification. Among small (< 4 cm) renal tumors, 4–13% are histologically confirmed as AML because imaging shows too little fat. Many authors have shown that AML with a small amount of fat is likely to have female predominance, small size, and a more homogeneous texture than RCC”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - Fat-rich AML should be differentiated from fat-containing RCC if this situation is rarely encountered. A small amount of fat relative to a large tumor, calcification, or necrosis is more suggestive of RCC than of AML. In exceptional cases, biopsy is recommended if these findings are detected.”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - “Fat-invisible AML should be differentiated from non–clear cell RCC. Both tumors tend to be hyperattenuating on unenhanced CT images, negative on chemical shift MR images, hypointense on T2- or fat- suppressed T2-weighted MR images, hyper- intense on DW images, and hypointense on ADC maps. Therefore, biopsy is necessary to differentiate these tumors.”
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588 - CT or MRI features can provide clues for differentiating fat-rich AML from fat-con- taining RCC and fat-poor AML from clear cell RCC. Fat-invisible AML, however, is difficult to differentiate from non–clear cell RCC on the basis of CT or MRI features. Radiologists should not be reluctant to perform biopsy when lesion differentiation is not clear at CT or MRI.
Renal Angiomyolipoma Based on New Classification: How to Differentiate It From Renal Cell Carcinoma
Byung Kwan Park
AJR 2019; 212:582–588
- “Appropriately selected cases of renal angiomyolipoma can be managed by active surveillance. For those patients requiring treatment nephron sparing approaches, including partial nephrectomy and selective arterial embolization, are preferred options. For those with tuberous sclerosis complex mTOR inhibitors may represent a viable approach to control tumor burden while conserving renal parenchyma.”
Update on the Diagnosis and Management of Renal Angiomyolipoma Flum, Andrew S. et al. The Journal of Urology , Volume 195 , Issue 4 , 834 - 846 - “The recommendation historically has been that patients with AMLs larger than 4 cm undergo intervention, especially in the setting of TSC. This size threshold is based on retrospective series showing that patients with tumors larger than 4 cm more often experienced hemorrhage and other symptoms, had interval growth and required intervention more often than those with AMLs smaller than 4 cm.”
Update on the Diagnosis and Management of Renal Angiomyolipoma Flum, Andrew S. et al. The Journal of Urology , Volume 195 , Issue 4 , 834 - 846 - “However, the authors argue that 67% of symptomatic patients and 66% with tumors larger than 4 cm could be maintained on surveillance, suggesting that following the historical criteria can result in overtreatment.25 Importantly no patient surveilled who ultimately underwent sur- gical resection had a malignancy on pathological examination.”
Update on the Diagnosis and Management of Renal Angiomyolipoma Flum, Andrew S. et al. The Journal of Urology , Volume 195 , Issue 4 , 834 - 846 - “Mirroring the evolution of surgical management for renal malignancies, surgery for AML has progressed from nephrectomy to open NSS to minimally invasive NSS. An attempt at NSS should be made in all patients when feasible, as it has been reported in the RCC literature that partial nephrectomy yields superior renal functional
outcomes and potentially improved overall mortality compared to nephrectomy. Use of NSS is even more critical in patients with TSC, as the multifocal and bilateral disease pattern with a higher rate of recurrence makes renal parenchymal preservation a key concern.”
Update on the Diagnosis and Management of Renal Angiomyolipoma Flum, Andrew S. et al. The Journal of Urology , Volume 195 , Issue 4 , 834 - 846
- “Patients with lymphangioleiomyomatosis (LAM) have a frequency of angiomyolipoma (AML) that varies from 20% to 54% depend-
ing on the method of patient or case collec- tion, imaging modality used, diagnostic criteria, and statistics of sampling variation. This frequency of AML is much higher than the reported frequency of 1–3% in the general population.”
Active Surveillance of Nonfatty Renal Masses in Patients With Lymphangioleiomyomatosis: Use of CT Features and Patterns of Growth to Differentiate Angiomyolipoma From Renal Cancer Nilo A. Avila et al. AJR 2017; 209:611–619 - “AMLs with no visible fat that are hyperattenuating relative to the normal renal parenchyma on unenhanced CT have been called “AML with minimal fat,” and AMLs that are hypoattenuating relative to the normal renal parenchyma but with attenuation values not in the range of fatty tissue on unenhanced CT have been termed “AML with diffusely scattered fat”. In this article, we use the term “nonfatty renal mass” to denote any renal mass with no visible fat on CT and the term “nonfatty AML” to denote an AML with no visible fat on CT.”
Active Surveillance of Nonfatty Renal Masses in Patients With Lymphangioleiomyomatosis: Use of CT Features and Patterns of Growth to Differentiate Angiomyolipoma From Renal Cancer Nilo A. Avila et al. AJR 2017; 209:611–619 - “Renal AML can be classified according to amount of fat as fat rich, fat poor, or fat invisible. To detect fat, one needs to thoroughly evaluate the entire AML by controlling the size and shape of the ROI. Fat-invisible AML should be biopsied, and fat-poor AML requires further investigation to determine whether biopsy is necessary to differentiate it from renal cell carcinoma. If differentiation between AML and renal cell carcinoma is not clear with CT and MRI, percutaneous biopsy may be performed.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835 - “Angiomyolipoma (AML) is the most common benign solid renal tumor. Most AMLs contain fat that is clearly visible on CT and MR images, so these tumors can be easily diagnosed without biopsy or surgery. Approximately 5% of renal AMLs, however, have too little fat to be identified in a CT or MRI examination. Preoperatively, these AMLs are difficult to differentiate from renal cell carcinoma (RCC) with radiologic examinations, and they frequently are diagnosed after surgery.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835 
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835-
“Unenhanced CT clearly depicts a hypoattenuating area (≤ –10 HU) suggesting fat in fat-rich AML. There- fore, detecting fat is not a problem in most fat-rich AMLs. However, some fat-rich AMLs have very small foci of fat measuring less than –10 HU, so these hypoattenuating areas may not be recognized at preoperative CT. Therefore, meticulous care should be taken not to miss a small focus of fat. Thin (< 5 mm) slice thickness (1.5–3 mm) should be used because thick (≥ 5 mm) slice thickness may not depict fat attenuation.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835 -
“Unenhanced CT cannot show fat attenuation in fat-invisible AMLs . These lesions appear homogeneously hyperattenuating because they have too little fat . The attenuation of fat-invisible AML is higher than that of fat-poor AML because the amount of fat in the former is lower than that in the latter. For this reason, the attenuation values of fat-invisible AML are fairly constant compared with those of fat- poor AML wherever an ROI is placed.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835
- “Contrast-enhanced CT is not necessary for diagnosing fat-rich AML but should be performed when there is potential for tumor bleeding. Frequently, large fat-rich AMLs contain a lot of tortuous or dilated vessels, which are susceptible to bleeding. Contrast-enhanced CT is essential to identify these abnormal vessels before embolization.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835 -
“Contrast-enhanced CT frequently shows heterogeneous enhancement within fat-poor AMLs because a small amount of fat is localized or scattered. Therefore, this type of AML may be misdiagnosed as clear cell RCC, which is heterogeneously enhancing on contrast-enhanced CT images. Still, it is unclear that fat-poor AML requires MRI or percutaneous biopsy. By definition, MRI is necessary to identify fat-poor AML. However, clear cell RCCs may have similar MRI features to those of these AML.”
Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat Byung Kwan Park AJR 2017; 209:826–835
- "The renal manifestations of tuberous sclerosis include angiomyolipomas, renal cysts, and renal cell carcinoma (RCC). Angiomyolipomas are the most common benign mesenchymal neoplasm and are composed of varying amounts of fat, smooth muscle, and blood vessels. Angiomyolipomas are present in 80% of patients with tuberous sclerosis. Angiomyolipomas due to tuberous sclerosis typically occur in younger patients and are frequently multiple and bilateral. Conversely, approximately 20% of patients with angiomyolipomas have tuberous sclerosis. The remainder of angiomyolipomas are sporadic (nontuberous sclerosis). Sporadic angiomyolipomas are usually unilateral and solitary and occur in middle-aged women. In addition, 2-3% of patients with tuberous sclerosis may have multiple renal cysts, given the proximity of the TSC2 gene to one of the genes on chromosome 16p13 that encodes for autosomal dominant polycystic kidney disease."
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43 - "The renal manifestations of tuberous sclerosis include angiomyolipomas, renal cysts, and renal cell carcinoma (RCC). Angiomyolipomas are the most common benign mesenchymal neoplasm and are composed of varying amounts of fat, smooth muscle, and blood vessels. Angiomyolipomas are present in 80% of patients with tuberous sclerosis. Angiomyolipomas due to tuberous sclerosis typically occur in younger patients and are frequently multiple and bilateral. Conversely, approximately 20% of patients with angiomyolipomas have tuberous sclerosis. The remainder of angiomyolipomas are sporadic (nontuberous sclerosis). Sporadic angiomyolipomas are usually unilateral and solitary and occur in middle-aged women."
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43 - "Most renal angiomyolipomas are asymptomatic. However, patients can present with flank pain, hematuria, hemorrhage, or a tender abdominal mass. Renal angiomyolipomas are the second most common cause of morbidity and mortality among patients with tuberous sclerosis. This risk can be attributed to an increased risk of rupture or hemorrhage of angiomyolipomas larger than 4 cm and aneurysms larger than 5 mm occurring within these tumors. If either of these criteria is met, treatment consists of resection or embolization. Tumors smaller than 4 cm are followed conservatively."
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43 - "The incidence of RCC among people with tuberous sclerosis is similar to that in the general population (2-3%) . However, the age at onset is much younger, and RCC in these patients tends to grow more slowly. The average age at diagnosis of RCC in tuberous sclerosis patients is 28 years, which is 25 years younger than in the general population. Tuberous sclerosis-associated RCCs are predominantly clear cell RCCs, but papillary and chromophobe RCCs have also been reported in the literature. The patterns of CT attenuation and homogeneity depend on the subtype, microvessel density, and presence of intratumoral necrosis or hemorrhage. Clear cell carcinomas are hypervascular and typically exhibit heterogeneous early enhancement and early washout. Papillary carcinomas tend to be hypovascular, usually enhancing in a gradual manner."
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43 - "The incidence of RCC among people with tuberous sclerosis is similar to that in the general population (2-3%) . However, the age at onset is much younger, and RCC in these patients tends to grow more slowly. The average age at diagnosis of RCC in tuberous sclerosis patients is 28 years, which is 25 years younger than in the general population. Tuberous sclerosis-associated RCCs are predominantly clear cell RCCs, but papillary and chromophobe RCCs have also been reported in the literature."
Comprehensive imaging manifestations of tuberous sclerosis.
Manoukian SB, Kowal DJ.
AJR Am J Roentgenol. 2015 May;204(5):933-43
- “Angiomyolipoma is the most common benign solid renal neoplasm observed in clinical practice. Once thought to be a hamartoma and almost always diagnosed by the imaged-based detection of fat, angiomyolipomas are now known to consist of a heterogeneous group of neoplasms. Although all are considered perivascular epithelioid cell tumors, many display different pathology, imaging features, and clinical behavior. The importance of understanding this group of neoplasms is emphasized by the fact that many types of angiomyolipoma contain little to no fat, and despite being benign, sometimes escape a pre-operative diagnosis.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Angiomyolipoma is a solid tumor that is encountered commonly in the kidney in clinical practice. Angiomyolipoma is typically a solid “triphasic” tumor composed of varying amounts of three elements: dysmorphic blood vessels, smooth muscle components, and mature adipose tissue . Because most angiomyolipomas contain substantial amounts of adipose tissue, it is usually diagnosed using CT or MRI by identifying imaging features of fat cells in the mass.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “The term perivascular epithelioid cell tumors (PEComa) was introduced by Zamboni et al. in 1996. In 2002 and 2003, two monographs published under the auspices of the WHO recognized a family of neoplasms with perivascular epithelioid cell (PEC) differentiation and coined the term, “PEComa” . PEComas are mesenchymal neoplasms composed of nests and sheets of predominantly epithelioid and some spindle cells that are associated with blood vessel walls, and the perivascular epithelioid cell or “PEC” (a cell that has no known normal tissue counterpart).”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Triphasic angiomyolipoma is a benign mesenchmal tumor composed of varying amounts of dysmorphic blood vessels, smooth muscle components, and mature adipose tissue. It occurs sporadically in less than 0.2% of people , typically during the 4th to 6th decade of life, and exhibits a female preponderance. Triphasic angiomyolipoma can be divided radiologically into “classic” and “fat poor subtypes.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “The image-based detection of fat often begins with CT . On unenhanced CT, the presence of regions of interest (ROI)-containing attenuations less than −10 HU allows the confident identification of fat . The CT appearance of a classic angiomyolipoma varies due to variable amounts of fat, blood vessels, and smooth muscle components of the neoplasm. These neoplasms do not contain smooth muscle; they reveal smooth muscle-like cells (hence the term “components”) which typically stain positive for HMB-45 and smooth muscle markers. When evaluating angiomyolipomas with a small amount of fat with CT, the acquisition of thin (1.5–3 mm) sections and obtaining attenuation measurements using small ROI or even pixel values may be necessary to detect fat that otherwise would not be detected because of partial volume-averaging.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “A fat-containing mass that originates in the kidney is likely an angiomyolipoma rather than liposarcoma. Identification of enlarged or bridging vessels, aneurysms, and perinephric hematomas are additional imaging features of angiomyolipoma that are rarely seen with liposarcoma.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Some triphasic angiomyolipomas contain too little fat (i.e., too few fat cells) to be detected with unenhanced CT; some have been diagnosed pre-operatively as RCC and inadvertently removed at surgery. These subtypes are now collectively referred to as “fat poor angiomyolipomas”. By definition, these lesions do not reveal fat at unenhanced CT, even when thin (1.5–3 mm) sections are used. In 1997, the term “angiomyolipoma with minimal fat” was introduced to describe angiomyolipomas that were hyperattenuating relative to renal parenchyma on unenhanced CT, homogeneously enhancing, and at pathology were composed almost entirely of a smooth muscle component and little to no fat.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Hyperattenuating angiomyolipoma is now the preferred term to describe a lesion that was originally described as an “angiomyolipoma with minimal fat”; these lesions represent approximately 4–5% of all angiomyolipomas . They are typically small and average 3 cm in diameter . At pathology, they generally contain only 4% (range, 3–10%) fat cells. The abundant smooth muscle component generally stains positive for HMB-45 antigen and smooth muscle markers.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Because of the abundant smooth muscle component, all hyperattenuating angiomyolipomas are hyperattenuating relative to renal parenchyma on unenhanced CT (usually more than 45 HU) similar to smooth muscle elsewhere, and typically homogeneously enhancing on CT.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Angiomyolipomas are observed in 55%–75% of patients with TSC; most form by the third decade . Relative to sporadic angiomyolipoma, both genders are affected equally. Angiomyolipomas in TSC typically present at a younger age, are more often multiple, larger, and almost always bilateral .”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - “Renal angiomyolipomas may also occur in patients with lymphangioleiomyomatosis (LAM), a rare disease characterized by proliferation of atypical smooth muscle-like cells with associated cystic changes. LAM typically presents with symptoms related to the destructive cystic changes in the lungs. The pulmonary disease is progressive and may result in pneumothoraces, chylous pleural effusions, and respiratory failure. LAM occurs sporadically or in association with TSC.”
Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management Jinzaki M et al. Abdom Imaging. 2014; 39(3): 588–604. - Renal Tumors that Contain Fat
• Angiomyolipoma
• Renal cell carcinoma
• Wilms tumor
• Teratoma
- “The estimated overall prevalence of angiomyolipoma worldwide is 0.3–3% . In most cases (80–90%), angiomyolipoma presents clinically as an isolated condition (i.e., sporadic angiomyolipoma); in the remaining 10–20% of cases, angiomyolipoma presents in association with tuberous sclerosis complex (TSC). TSC is an autosomal dominant disease that leads to the formation of tumors in multiple organs, including the brain, lungs, skin, liver, and kidneys . Approximately 70–90% of individuals with TSC have renal angiomyolipoma by adulthood .”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301 - “Several demographic and clinical differences have been noted between patients pre-senting with sporadic angiomyolipoma and those presenting with TSC-associated angiomyolipoma. TSC-associated angiomyolipoma is usually diagnosed at a younger age (sometimes during childhood) than sporadic angiomyolipoma, and a predominance in females has been suggested. Boorjian et al. noted that lesions from patients with TSC were significantly more likely to express both estrogen receptors and progesterone receptors, compared with lesions from patients with sporadic angiomyolipomas. The increased growth of TSC-associated angiomyolipomas in female patients during adolescence and pregnancy may be caused by hormonal influence.”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301 - “Several demographic and clinical differences have been noted between patients pre-senting with sporadic angiomyolipoma and those presenting with TSC-associated angiomyolipoma. TSC-associated angiomyolipoma is usually diagnosed at a younger age (sometimes during childhood) than sporadic angiomyolipoma, and a predominance in females has been suggested. Boorjian et al. noted that lesions from patients with TSC were significantly more likely to express both estrogen receptors and progesterone receptors, compared with lesions from patients with sporadic angiomyolipomas.”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301 - “On CT , renal angiomyolipoma typically appears as a well-marginated cortical predominantly fat-attenuated mass with heterogeneous soft-tissue attenuation interspersed throughout the lesion. Soft-tissue attenuation may be the result of hemorrhage or fibrosis, or it may be a manifestation of the vascular or smooth muscle components of the lesion. Finally, angiomyolipoma-associated retroperitoneal hemorrhage may mask characteristic fat, rendering differentiation from RCC difficult.”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301 - “Tumor size is used to predict the risk of bleeding and the need for preemptive surgical management versus continued observation. In a retrospective review of the literature by Oesterling et al., in 82% of patients with tumors larger than or equal to 4 cm, tumors were symptomatic (i.e., producing abdominal pain, nausea, vomiting, fever, shock, hypertension, palpable abdominal mass or flank pain, tenderness, or anemia), and hemorrhage occurred in more than half of these patients. Size alone was not a predictor of hemorrhage; 10 patients with angiomyolipomas smaller than 4 cm experienced hemorrhage.”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301 - “We are entering a new era in the management of TSC and other mTOR-mediated genetic diseases, such as Peutz-Jegher, Cowden, and Proteus syndromes. With the development of mTOR inhibitors, we have long-term therapy directed at the molecular pathway that leads to TSC-related tumors. In patients with TSC, brain (SEGA), lung (lymphangioleiomyomatosis), and kidney (angiomyolipoma) manifestations have often been treated by different specialists without overlapping management strategies. With the advent of mTOR inhibition, all apects of TSC will need to be considered in deciding which patients should receive therapy and in monitoring responses.”
Differentiation of Sporadic Versus Tuberous Sclerosis Complex–Associated Angiomyolipoma Rabenou RA, Charles HW AJR 2015; 205:292–301
- “AML can haemorrhage, with intra-tumoural aneurysm size >5 mm a more specific predictor of future haemorrhage than tumor size >4 cm. Diagnosis of AML in the setting of acute haemorrhage is complex; comparison studies or follow-up imaging may be required. Not all AML contain gross fat and imaging features of AML without visible fat overlap with RCC; however, homogeneity, hyperdensity at NECT, low T2-weighted signal intensity and, microscopic fat are suggestive features.”
Ten uncommon and unusual variants of renal angiomyolipoma (AML): radiologic-pathologic correlation.
Schieda N et al.
Clin Radiol. 2015 Feb;70(2):206-20 - “Patients with tuberous sclerosis often demonstrate a combination of classic and minimal fat AML, but are also at a slightly increased risk for RCC and should be imaged cautiously. Several rare pathological variants of AML exist including AML with epithelial cysts and epithelioid AML, which have distinct imaging characteristics. Classic AML, although benign, can be locally invasive and the rare epithelioid AML can be frankly malignant.”
Ten uncommon and unusual variants of renal angiomyolipoma (AML): radiologic-pathologic correlation.
Schieda N et al.
Clin Radiol. 2015 Feb;70(2):206-20 - “Prophylactic embolization of pseudoaneurysms detected on early postoperative CT can prevent delayed hemorrhage after partial nephrectomy, without major complications.”
Early Postoperative Screening by Contrast-Enhanced CT and Prophylactic Embolization of Detected Pseudoaneurysms Prevents Delayed Hemorrhage after Partial Nephrectomy.
Morita S
J Vasc Interv Radiol. 2015 Apr 13. pii: S1051-0443(15)
- “ Specific CT features can potentially be used to differentiate lipid-poor renal angiomyolipoma from renal cell carcinoma.”
Are There Useful CT Features to Differentiate Renal Cell Carcinoma From Lipid-Poor Renal Angiomyolipoma
Yang CW et al.
AJR 2013; 201:1017-1028 - “ The CT diagnosis of angiomyolipoma relies on the detection of areas of macroscopic fat, with negative attenuation measurements. However no fat can be visualized in approximately 4.5% of angiomyolipoma.”
Are There Useful CT Features to Differentiate Renal Cell Carcinoma From Lipid-Poor Renal Angiomyolipoma
Yang CW et al.
AJR 2013; 201:1017-1028 - “ The CT diagnosis of angiomyolipoma relies on the detection of areas of macroscopic fat, with negative attenuation measurements. However no fat can be visualized in approximately 4.5% of angiomyolipoma. These tumors are referred to as lipid poor renal angiomyolipomas. Patients with lipid poor renal angiomyolipoma usually receive unnecessary surgery for suspected renal cell carcinoma when the diagnosis is not specifically established prospectively.”
Are There Useful CT Features to Differentiate Renal Cell Carcinoma From Lipid-Poor Renal Angiomyolipoma
Yang CW et al.
AJR 2013; 201:1017-1028 - “ The enhancement pattern over time was similar in clear-cell RCC and lipid poor angiomyolipoma, with prominent enhancement in the corticomedullary phase and a slight washout in the nephrographic phase. Tumor attenuation in the nephrographic phase was significantly lower for lipid poor angiomyolipoma than for clear cell RCC.”
Are There Useful CT Features to Differentiate Renal Cell Carcinoma From Lipid-Poor Renal Angiomyolipoma
Yang CW et al.
AJR 2013; 201:1017-1028 - “ In conclusion, an angular interface, hypodense rim, homogeneous enhancement pattern, and high unenhanced attenuation are specific CT features that may suggest lipid-poor renal angiomyolipoma and have high negative predictive value of renal cell carcinoma. By careful assessment of these features, unnecessary surgery may be avoided.”
Are There Useful CT Features to Differentiate Renal Cell Carcinoma From Lipid-Poor Renal Angiomyolipoma
Yang CW et al.
AJR 2013; 201:1017-1028