Imaging Pearls ❯ Kidney ❯ Renal Cysts and Cystic Disease
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- “ Potential pitfalls in the application of Bosniak v2019 are divided into three categories: interpretative, technical, and mass related. An organized, comprehensive review of possible discrepancies in interpreting Bosniak v2019 cystic masses is presented with pictorial examples of difficult clinical cases and proposed solutions. The scheme provided can guide readers to consistent, precise application of the classification system. Radiologists should be aware of the possible sources of misinterpretation of cystic renal masses when applying Bosniak v2019. Knowing which features and types of cystic masses are prone to interpretive errors, in addition to the inherent trade-offs between the CT and MR techniques used to characterize them, can help radiologists avoid these pitfalls.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - “ We broadly classified potential pitfalls when applying Bosniak v2019 into three categories: (1) interpretative related to quantifying or determining appropriate classification of cystic mass features; (2) technical pertaining to the imaging modalities themselves; and (3) mass-related inherent characteristics of certain cystic masses that are prone to misclassification. The recommendations provided herein represent the consensus opinion of the authors, but the clinical judgment of the interpreting radiologist remains important.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) 
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press)- "Bosniak v2019 eliminated the need to distinguish “perceived” from “measurable” enhancement, instead clearly defining enhancement as either unequivocally visibly perceived, or established using a quantitative threshold (≥ 20 HU increase at CT, or ≥ 15% signal intensity increase at MRI [12]). Bosniak v2019 permits features to enhance in benign classes I and II (e.g., a thin smooth wall), but requires features to enhance in classes IIF (except those that are heterogeneously T1-hyperintense), III, and IV. Therefore, a potential interpretative pitfall would be to count or measure non-enhancing septa (e.g., at T2-weighted imaging) when assigning Bosniak v2019 classes IIF and III.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - “Technical parameters at CT may influence the determination of homogeneity or heterogeneity within a cystic renal mass. For example, as CT dose is decreased, increased image noise may cause a homogeneous structure to appear heterogeneous. A similar phenomenon is observed when imaging with very thin section reconstruction intervals (e.g., < 1 mm), since decreased voxel size increases CT image noise.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - "The amount of iterative reconstruction used to reconstruct the final image from the raw data set is typically variable and user determined. However, if levels are set too high, images may become overly smoothed, having an unfamiliar ‘plastic’-appearing texture. Subtle heterogeneities and internal features in renal masses could be overlooked. Similarly, accurate identification of imaging features in a cystic renal mass depends on an optimal dosage and timing of contrast material.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - "Benign diagnoses can be erroneously attributed to cystic malignancies. These include pyelonephritis, abscess, hematoma, inflammatory disorders, aneurysms and vascular malformations, and pseudomasses. These can be considered cognitive errors rather than imaging pitfalls, as patient history, laterality, and perinephric inflammation usually suggest such alternative diagnoses. These alternative diagnoses must be excluded before the application of Bosniak v2019.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - “A homogeneous mass measuring − 9 to 20 HU at renal mass protocol or single-phase enhanced CT with a thin (≤ 2 mm) and smooth wall is considered a Bosniak v2019 class I simple cyst. Since many cystic masses are incidentally discovered in patients undergoing only unenhanced CT, Bosniak v2019 permits establishing a reliable benign diagnosis using only unenhanced CT without the need for ultrasound, renal mass protocol CT, or MRI.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press) - "Bosniak v2019 created more precise definitions for previously subjective terms, allowed for more cystic masses to be characterized, and broadened the imaging features that can be considered benign. As such, its increased implementation is expected to lead to more consistent reported malignancy rates within each class, greater interreader agreement, and fewer benign masses being resected at surgery. However, future studies are needed to assess its success in these areas.”
Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification
Elizabeth Edney et al.
Abdominal Radiology (in press)
- “Multilocular cystic nephroma is a rare and benign renal neoplasm with an excellent prognosis. It has a bimodal distribution in children within 2 years of age with a male predominance and in adults over 30 years of age with a female predominance.Most cases are asymptomatic and found incidentally during imaging investigation.”
Multilocular cystic nephroma: A case report and review of the literature
Chih-Peng Chang et al.
Urological Science Volume 25, Issue 4, December 2014, Pages 109-111 - “On the image study, a multilocular, cystic nephroma appears as a multilocular cyst with multiple septa, using contrast enhancement, and watery fluid inside the cyst. Sometimes, extension into the renal pelvis may be seen, which results in hydronephrosis and hemorrhage.”
Multilocular cystic nephroma: A case report and review of the literature
Chih-Peng Chang et al.
Urological Science Volume 25, Issue 4, December 2014, Pages 109-111 - “Multilocular cystic renal cell carcinoma cannot reliably be distinguished from cystic nephroma neither by physical examination nor by radiologic evaluation; immunohistochemical staining assay is useful to differentiate between these conditions allowing an accurate diagnosis and proper follow-up.”
Multilocular Cystic Renal Cell Carcinoma or Cystic Nephroma?
Adolfo González-Serrano
Case Reports in Urology, vol. 2016, Article ID 5304324, 4 pages, 2016.
- Multilocular cystic masses
are radiologically indeterminate
Differential diagnosis includes
- Cystic renal cell carcinoma
- Cystic nephroma
- Localized XGP
- Localized renal cystic disease
- Abscess - Oncocytic Neoplasms: Facts
- Fairly common diagnosis (9% of SRMs)
- No technique to differentiate oncocytic RCC from oncocytoma with 100% reliability from imaging or biopsy
- Hybrid tumors: oncocytoma and RCC coexist in one tumor in up to 17% of “oncocytomas” - CT Urography: Indications
- Hematuria
- High risk of upper urinary tract malignancy
- New bladder carcinoma patients
- Surveillance following malignancy treatment
- Evaluation of congenital urinary tract anomalies
- Evaluation of ureteral obstruction
- Evaluation after upper tract surgery
- Suspected ureter injury
- Problems with Bosniak Classification
- Difficulty deciding between cat. 2 and cat. 3
- Important Rx implications
- Relatively frequent problem
- Wall or septum too thick?
- > 3 cm in diameter
- Equivocal enhancement
- Or, if there are Sx (e.g., hematuria)
- Call these “2F” (need follow-up)
-- Repeat scans in 3, 6, and 12 months, then annually
- Follow for 5 years (cystic RCCs are slow growing) - Bosniak Category 1:
Simple Renal Cyst
Features:
1. Imperceptible or hairline walls
2. No septa, calcifications or solid components
3. Water attenuation
4. No enhancement
- < 20 HU change is probably “pseudoenhancement”
5. Management: Ignore - Bosniak Category 2
Features
1. Few hairline-thin septa without measureable enhancement
2. May have thin calcification in septa or wall
3. (Subtype): Hyperdense cyst
- Homogeneously high attenuation (usually > 70 HU)
- - 3 cm diameter
- Nonenhancing
4. Management: Ignore - Cystic Renal Masses
Category 2 – Benign, Minimally Complicated
Hyperdense Cyst
- Usually not due to acute bleed
- These may have fluid – debris level
- Same density on unenhanced and enhanced (usually 70 – 100 HU) - Bosniak Category 3:
Complex Cyst or Neoplasm
Features:
- Thickened, irregular walls or septa with measurable enhancement
Management:
- Surgery for most patients
- Observe (or even ignore) for those with serious comorbidities or limited life expectancy - Bosniak Category 4:
Cystic Neoplasm
Features:
- Same as for Category 3, but also with enhancing soft tissue components
Management:
- Surgery for most
- Nephron-sparing if small + accessible
- Observe (or even ignore) for those with serious comorbidities or limited life expectancy - Multilocular Cystic Nephroma
(Multilocular Renal Cyst)
- Multiple non-communicating cysts
- Surrounded by thick capsule
- Septa enhance, may calcify
- Herniation into renal pelvis
- Usually boys and middle age women
- Caution!
- RCC can have identical appearance
- “ The classification of renal cystic lesions suggested 25 years ago, now referred to as the Bosniak renal cyst classification, remains pertinent to the diagnosis and management of these difficult to diagnose complicated cystic masses.”
The Bosniak Renal Cyst Classification: 25 Years Later
Bosniak MA
Radiology 2011; 262:781-785 - “ Pseudoenhancement of renal cysts significantly correlates with size smaller than 1 cm and central location. Although pseudoenhancement increase with larger numbers of detectors, the correlation was not statistically significant. Cysts in the 1- to 1.5 cm range have a 19% likelihood of pseudoenhancement.”
Pseudoenhancement of Renal Cysts: Influence of Lesion Size, Lesion Location, Slice Thickness, and Number of MDCT Detectors
Tappouni R et al.
AJR 2012; 198:133-137 - “ Renal cysts are common in adults, and the prevalence increases with age to greater than 27% in patients older than 50 years.”
Pseudoenhancement of Renal Cysts: Influence of Lesion Size, Lesion Location, Slice Thickness, and Number of MDCT Detectors
Tappouni R et al.
AJR 2012; 198:133-137 - “ A less than 10 HU increase in attenuation is considered within the technical limits of the study and is not considered to represent enhancement.”
Pseudoenhancement of Renal Cysts: Influence of Lesion Size, Lesion Location, Slice Thickness, and Number of MDCT Detectors
Tappouni R et al.
AJR 2012; 198:133-137
" Diagnostic performance in characterizing lesions as benign or malignant, however, is not statistically different for the thick and thin images."
Characterization of Atypical Cystic Renal Masses with MDCT: Comparison of 5-mm Axial images and Thin Multiplanar Reconstructed Images
Bertolotto M et al
AJR 2010; 195:693-700"Analysis of volume data sets is associated with less intraobserver and interobserver variability of 5-mm axial images. Wall thickness and the number and thickness of septa may differ, resulting in assignment of different Bosniak categories."
Characterization of Atypical Cystic Renal Masses with MDCT: Comparison of 5-mm Axial images and Thin Multiplanar Reconstructed Images
Bertolotto M et al
AJR 2010; 195:693-700- Localized Renal Cystic Disease : facts
- Conglomerate mass of multiple simple cysts of various sizes, seperated by enhancing or atrophic renal tissue
- Cysts may involve entire kidney or portion of the kidney
- Typically kidney will show normal excretion of contrast material
- Benign condition which does not progress to renal failure "Also known as segmental renal cystic disease and unilateral renal cystic disease, localized renal cystic disease is a rare, nonhereditary, noprogressive condition that is characterized by multiple cysts in one kidney, with no cysts in the other kidney or other organs."
Adult Renal Cystic Disease: A Genetic, Biological, and Developmental Primer
Katabathina VS et al.
RadioGraphics 2010; 30:1509-1523- Autosomal Dominant Polycystic Renal Disease: Extrarenal Manifestations
- Hepatic cysts
- Pancreatic cysts
- Seminal vesicle cysts
- Splenic cysts
- Intracranial arterial aneurysms
- Aortic aneurysms
- Abdominal wall hernias
- Colonic diverticula
- Aortic and mitral valve abnormalities - Autosomal Dominant Polycystic Renal Disease: Complications
- Infection
- Hemorrhage
- Cyst rupture
- End stage renal disease (45% of patients) develops by age 60 - Autosomal Dominant Polycystic Renal Disease: Facts
- Most common hereditary renal cystic disease
- Occurs in one in 400-1000 live births
- Affects 300,000 to 600,000 Americans
- 3rd most common cause of end stage renal disease
- 90% of cases are hereditary in nature
- Mutation in gene PKD1 and PKD2 "Patients with autosomal dominant polycystic kidney disease have a mean renal volume of more than 1000 mL (the normal mean is 150 mL) and an age related increase in total renal volume and total cyst volume, with a mean annual increase of 63.4 mL in renal volume."
Adult Renal Cystic Disease: A Genetic, Biological, and Developmental Primer
Katabathina VS et al.
RadioGraphics 2010; 30:1509-1523"Renal cystic diseases in adults are a heterogenous group of disorders characterized by the presence of multiple cysts in the kidney. These diseases may be categorized as hereditary, acquired, or developmental on the basis of their pathogenesis."
Adult Renal Cystic Disease: A Genetic, Biological, and Developmental Primer
Katabathina VS et al.
RadioGraphics 2010; 30:1509-1523- Medullary Sponge Kidney: Facts
- Congenital developmental abnormality characterized by ectasia and cystic dilatation of the intrapyramidal or intrapapillary portions of the renal medullary collecting ducts
- Occurs in 1 in 5,000 patients
- Usually sporadic cases
- Usually detected incidentally although some patients present with renal colic, hematuria, and urinary tract infections - Select Renal Cystic Diseases in Adults
Hereditary disease
- Autosomal dominant polycystic kidney disease
- Medullary cystic renal disease
- Von Hippel-Lindau disease
- Tuberous sclerosis complex
Nonhereditary disease
- Acquired cystic kidney disease
- Medullary sponge kidney
- Multicystic dysplastic kidney
- Localized renal cystic disease - Polycystic Kidney Disease: Differential Dx (in theory)
- Multiple simple cysts
- Von Hippel-Lindau disease
- Acquired uremic cystic disease
- Infantile PCKD - Polycystic Kidney Disease: Clinical Presentation
- Hypertension
- Azotemia
- Hematuria
- Proteinuria
- Abdominal or back pain - Polycystic Kidney Disease: Facts
- Autosomal dominant with nearly a 100% penetrance
- Defect on short arm of chromosome 16
- Cysts also occur in liver (up to 80% of cases), and pancreas (up to 9% of cases)
- Patients may also have an increased incidence of cerebral aneurysms - Cystic Renal Masses
- Cystic clear cell carcinoma
- Multilocular cystic renal cell carcinoma
- Cystic Nephroma
- Mixed Epithelial and Stromal tumors (MEST)
- Complex benign cystic renal lesions "Because cystic renal cell carcinomas, benign complicated cysts, and other cystic tumors can be in distinguishable at gross pathologic inspection, and a definitive diagnosis can require a histologic examination, an overlap in imaging findings is not unexpected."
Clinical and Radiologic Features of Cystic Renal Masses
Freire M, Remer EM
AJR 2009; 192:1367-1372- "Given the distribution of cyst and tumor attenuation values and lesion heterogeneity, a homogeneous mass measuring 70 HU or greater at unenhanced CT has a greater than 99.9% chance of representing a high-attenuation renal cyst."
Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhance CT?
Jonisch AI et al.
Radiology 2007; 243:445-450
- "The findings from this study may help differentiate high attenuation renal cysts from renal cell carcinomas at unenhanced CT and may suggest the next appropriate imaging study for definitive characterization."
Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhance CT?
Jonisch AI et al.
Radiology 2007; 243:445-450
- "Greater than 95% of high attenuation renal cysts are homogeneous in attenuation."
Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhance CT?
Jonisch AI et al.
Radiology 2007; 243:445-450
- "A homogeneous renal mass measuring greater than 70 HU at unenhanced CT has a greater than 99.9% chance of representing a high attenuation renal cyst rather than a renal cell carcinoma."
Can High-Attenuation Renal Cysts Be Differentiated from Renal Cell Carcinoma at Unenhance CT?
Jonisch AI et al.
Radiology 2007; 243:445-450
- What is a Bosniak IIF?
- Cysts with multiple septae with minimal thickening or calcification which is thick and nodular or intrarenal non-enhancing high density (>3cm) lesion
- These lesions are felt to be benign and routine follow-up advised
- The Bosniak Renal Cyst Classification System
- Category I
- Category II
- Category IIF
- Category III
- Category IV
- von Hippel-Lindau Disease: Renal Pathology
- Renal cysts- occur in 50-75% of patients and are usually multiple and bilateral
- Renal cell carcinoma-occur in 28-45% of patients and occur at a younger age (30-36 yrs). The lesions are often multiple and bilateral and may be hypovascular or cystic lesions with mural nodules
- von Hippel-Lindau Disease: Adrenal Pathology
- Pheochromocytoma
- Occur in up to 30% of families with VHL
- They are bilateral in up to 50% of patients with a malignancy rate of around 10%
- Up to 18% are extraadrenal in location
- "On portal venous phase contrast enhanced CT scans, attenuation greater than 70HU or moderate or marked internal heterogeneity favor a diagnosis of renal cell carcinoma oer a diagnosis of high attenuation renal cyst."
Distinction of Renal Cell carcinomas from High Attenuation Renal Cysts at Portal Venous Phase Contrast Enhanced CT
Suh M et al
Radiology 2003; 228:330-334
- Sickle Cell Disease:Organ Involement
- Bone
- Brain
- Lungs
- Liver
- Spleen
- Kidney
- Sickle Cell Disease: Subgroups
- SS disease (homozygous Hb SS)
- SC disease
- S-thal
- Sickle Cell trait is associated with a rare renal tumor- medullary carcinoma.