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Benign Renal Masses

  • “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.”

    Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management.
    Jinzaki M et al.
    Abdom Imaging. 2014 Jun;39(3):588-604.
  • “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. These types of angiomyolipomas can all be considered when encountering a renal mass that is both hyperattenuating relative to renal parenchyma on unenhanced CT and T2-hypointense, features that reflect their predominant smooth muscle component.” 

    Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management.
    Jinzaki M et al.
    Abdom Imaging. 2014 Jun;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 Jun;39(3):588-604.
  • “While 80% of angiomyolipomas are sporadic and most of them inconsequential, approxi- mately 20% are associated with tuberous sclerosis complex (TSC) . Angiomyolipomas may be found also in patients with lymphangioleiomyomatosis (LAM) .” 

    Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management.
    Jinzaki M et al.
    Abdom Imaging. 2014 Jun;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.” 

    Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management.
    Jinzaki M et al.
    Abdom Imaging. 2014 Jun;39(3):588-604.
  • “Excellent classification results (error of 0.00%-9.30%) were obtained with nonlinear discriminant analysis for all the three groups, no matter which phase was used. On comparison of the three scanning phases, we observed a trend toward better lesion classification with PCP for minimal fat AML versus ccRCC, CMP, and NP images for ccRCC versus pRCC and found similar discriminative power for minimal fat AML versus pRCC.”
    Angiomyolipoma with Minimal Fat: Differentiation From Clear Cell Renal Cell Carcinoma and Papillary
    Renal Cell Carcinoma by Texture Analysis on CT Images.
    Yan L et al.
    Acad Radiol. 2015 May 29. pii: S1076-6332(15)00188-9
  • Extramedullary Hematopoesis: Facts
    - Compensatory mechanisms to form blood cells within organs or tissues outside the bone marrow
    - Usually occurs in spleen, liver, lymph nodes, paraspinal soft tissues
    - Can mimic adenopathy or a primary tumor especially a neurogenic tumor
    - The masses often are vascular on contrast enhanced CT
  • Perinephric Masses on CT: Differential Diagnosis
    - Lymphoma
    - Metastases (especially melanoma)
    - Myeloma
    - Urinomas
    - Hemmorrhage
    - Infection
    - Extramedullary hematopoiesis
    - Retroperitoneal fibrosis
    - Erdheim Chester disease
  • Benign Lesions of the Upper Urinary Tract: Mimics
    - Malacoplakia
    - Urolithiasis
    - Infection
    - TB
    - Fibroepithelial polyps
    - Sloughed papilla
    - Hematoma
  • Mesenchymal Renal Neoplasms: Benign
    - Angiomyolipoma
    - Leiomyoma
    - Hemangioma
    - Lymphangioma
    - Juxtaglomerular cell tumor
    - Medullary fibroma
    - Solitry fibrous tumor
    - Schwannoma
  • Mesenchymal Tumors

    - Angiomyolipoma
    - Leiomyoma
    - Hemangioma
    - Lymphangioma
    - Reninoma
    - Fibroma
    - Schwannoma
  • Mixed Epithelial and Mesenchymal Tumors

    - Cystic nephroma
    - Mixed epithelial and stromal tumor
  • A Pattern-Based Imaging Approach to Benign Renal Tumors

    - Soft tissue mass
    - Fatty mass
    - Cystic mass
    - Cortical mass
    - Medullary mass
    Benign Renal Neoplasms in Adults:
    Cross-Sectional Imaging Findings
    Prasad SR et al. AJR 2008; 190:158-164
  • Mixed Epithelial and Mesenchymal Neoplasms: Facts

    - Consists of mixed epithelial and stromal tumors (MEST) and cystic nephromas
    - MEST was previously called
    –Leiomyomatous renal hamartoma
    –Multilocular cyst with ovarian stroma
    –Cystic hamartoma of the renal pelvis
    –Adult mesoblastic nephroma
  • Mixed Epithelial and Stromal Tumors (MEST)

    - Usually in perimenopausal woman by 6:1 ratio
    - Most patients are on estrogen therapy
    - 25% of cases are detected incidentally
    - CT findings are expansile, complex, cystic and solid masses with heterogeneous and delayed enhancement
  • Cystic Nephroma: Facts

    - Benign tumor in middle aged females
    - CT findings are a well demarcated solitary multilocular cystic lesions with thin septations. These tumors may protrude into the renal pelvis and cause hemorrhage or urinary obstruction
  • Proportion of Solid Renal Masses That are Benign:

    Size (cm)Proportion
    All sizes12.8%
    0 to < 146.3%
    1 to < 222.4%
    2 to < 322.0%
    3 to < 419.9%
    4 to < 59.9%
    5 to < 613.0%
    6 to < 74.5%
    > 76.3%
  • Fact: small renal masses removed at surgery are often benign
    Solid Renal Tumors: An Analysis of Pathological Features Related to Tumor Size
    Frank I et al.
    J Urol 2003; 170:2217-2220
  • Extramedullary Hematopoiesis: Facts

    - Hematopoietic tissue develops outside primary medullary sites
    - Associated with hemolytic anemias, henoglobinopathies, myelofibrosis, leukemia, lymphoma
    - Most common sites are liver, spleen and parespinal regions of the thorax
  • Benign Renal Neoplasms in Adults: WHO Classification

    - Renal cell tumors (Oncocytoma)
    - Metanephric neoplasms
    - Mesenchymal neoplasms
    - Mixed epithelial and mesenchymal neoplams
  • Renal Cell Tumors

    - Oncocytoma - Papillary adenoma
  • Metanephric Tumors - Metanephric adenoma - Metanephric adenofibroma - Metanephric stromal tumor
  • Mesenchymal Tumors

    - Angiomyolipoma - Leiomyoma - Hemangioma - Lymphangioma - Reninoma - Fibroma - Schwannoma
  • Mixed Epithelial and Mesenchymal tumors

    - Cystic nephroma
    - Mixed epithelial and stromal tumor
  • "The 2004 World Health Organization (WHO) classification schemata categorizes benign renal neoplasms on the basis of histiogenesis (cell of origin) and histopathology."

    Benign Renal Neoplasms in Adults: Cross-Sectional Imaging Findings
    Prasad S et al.
    AJR 2008; 190:158-164
  • "The 2004 World Health Organization (WHO) classification schemata categorizes benign renal neoplasms on the basis of histiogenesis (cell of origin) and histopathology. Renal neoplasms are thus classified into renal cell, metanephric, mesenchymal, and mixed epithelial and mesenchymal tumors."

    Benign Renal Neoplasms in Adults: Cross-Sectional Imaging Findings
    Prasad S et al.
    AJR 2008; 190:158-164
  • Oncocytoma: facts

    - Benign renal cell neoplasm
    - Patient usually in 6th or 7th decade of life
    - Male more commonly involved
    - Central scar seen in 1/3 of cases on CT
    - May be indistinguishable from renal cell carcinoma
  • Oncocytoma: facts

    - Up to 40% of patients over age 70 will have these tumors at autopsy
    - Commonly found in patients with acquired cystic renal disease and patient on long term hemodialysis
    - Usually measure 5 mm or less
  • Metanephric Adenoma: facts

    - Benign tumor
    - 2:1 female predominance
    - Average age is 5th or 6th decade
    - Polycythemia occurs in 10% of patients
  • Juxtaglomerular cell Neoplasm (Reninoma): facts

    - Benign tumor of myoendocrine origin
    - Peak age is2nd or 3rd decade of life
    - 2:1 female predominance
    - Clinical triad of poorly controlled hypertension, hypokalemia and high plasma renin level
    - Usually under 3 cm vascular tumor
  • Juxtaglomerular cell Neoplasm (Reninoma): facts

    - Occur in perimenopausal woman often receiving estrogen
    - 6:1 female predominance
    - On CT usually large cystic and solid tumors which heterogeneous and delayed enhancement
  • Juxtaglomerular cell Neoplasm (Reninoma): facts

    "In an anthropomorphic phantom model, dual energy CT can accurately discriminate uric acid stones from other stone types."

    Noninvasive Differentiation of Uric Acid versus Non-uric Acid Kidney Stones Using Dual Energy CT
    Primak AN et al
    Acad Radiol 2007; 14:1441-1447
  • Juxtaglomerular cell Neoplasm (Reninoma): facts

    "An mA as low as 70 (35 mAs) is acceptable for evaluation of nephrolithiasis. However, the evaluation of ureterolithiasis is comprimised with an mA of 70."

    Conventional and Reduced radiation Dose of 16-MDCT for Detection of Nephrolithiasis and Ureterolthiasis
    Paulson EK et al.
    AJR 2008; 190;151-157