This document discusses ultrasound findings of renal cysts and cystic renal lesions. It provides details on:
1) The Bosniak classification system used to characterize renal cysts and cystic masses as benign (Classes I and II) or malignant (Classes III and IV).
2) Characteristics of simple renal cysts, complex cysts, cystic renal cell carcinomas, and other cystic lesions.
3) Cystic manifestations of conditions like polycystic kidney disease, von Hippel-Lindau disease, and tuberous sclerosis.
1. Ultrasound of the urinary tract
Renal cysts
Samir Haffar M.D.
Department of Internal Medicine
2. Ultrasound of renal cysts
• Common in population > 50 years (at least 50%)
• Scanning technique is important
Multiple positions: supine, LD, oblique, prone
Scan with appropriate focal zone
• Better demonstrated with THI: reduced background noise
• Main goal: differentiate surgical from nonsurgical lesion
Bosniak classification: based on CT scan
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
3. Bosniak classification
Used worldwide in evaluating cystic renal masses
• Originally described in 1986 & updated later
• Not a pathologic but imaging & clinical management system
• Developed on CT findings but applied to other modalities
US Cannot alone accurately characterized cystic mass
Except if renal mass is cystic (CT pseudoenhancement)
MRI Often used when CECT contraindicated
Higher Bosniak category than CT in some cases
Israel GM & Bosniak M. Radiology 2005 ; 236 : 441 – 450.
4. Bosniak classification of renal cysts
Category CT features Significance
Class I Water density homogenous
Noncalcified, smooth margin
No enhancing component
Benign
Chapple CR et al. Practical urology: Essential principles & practice.
Springer-Verlag, London , 2011.
Class II Thin septae (<1 mm)
Thin calcification (<1 mm)
Hemorrhagic cyst
Benign
Class IIF Likely benign
Follow-up imaging indicated
Class III Thick septa
Thick calcification
Thick wall
Multilocular +/− enhancement
≈ 50% malignant
Class IV Criteria of category III
Enhancing solid mass of wall or septa
Definitely malignant
5. Simple cortical cyst
Bosniak category I cyst
Bosniak MA. Radiology 1986 ; 158 : 1 – 10.
Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41.
Three characteristics
- Anechoic
- Sharply defined smooth wall
- Posterior acoustic enhancement
If all these sonographic criteria are met
Further evaluation or follow-up is not required
6. Tissue harmonic imaging (THI)
Probable cyst on right kidney
Evident internal echoes
Gray-scale US
THI “cleaned-up” image
Removing internal echoes
Simple renal cyst
Application of THI
McGahan J et al. Diagnostic ultrasound, Informa Healthcare, 2nd edition, 2008.
7. Better lateral & axial resolution
Enhanced signal-to-noise ratio
Reduced artifacts
Theoretic advantages of THI
Less degradation of sonographic images
8. Milk of calcium renal cyst
Renal cyst with dependent echogenic material
Mobile on real-time examination
This kind of cyst is always benign
Rumack CM et al. Diagnostic Ultrasound. Elsevier-Mosby, St. Louis, USA, 3rd edition, 2005.
9. Complex renal cyst
Do not meet strict US criteria of simple renal cyst
• 5-10% of all renal cysts are not simple cysts
• 5-10 % of complex renal cysts prove to be tumors
• Complex cysts: Wall thickening
Septations & nodularity
Calcification
High attenuation (>20 HU at CT )
Signal not typical of water at MRI
Enhancement
• 2 main causes Complicated simple cyst, cystic RCC
Hartman DS et al. RadioGraphics 2004 ; 24 : S101 – S115.
10. Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41.
Minimally complicated renal cyst
Bosniak category II cyst
Renal cyst with thin septation
Artifact from septation
Frequently seen at real-time US
11. Cyst with mural nodule Complex cystic renal lesion
Thick nodular septations
Rumack CM et al. Diagnostic Ultrasound. Elsevier-Mosby, St. Louis, USA, 3rd edition, 2005.
Complicated renal cyst
Bosniak category III cyst
12. Cystic growth patterns of renal cell carcinoma
Yamashita Y et al. Acta Radiologica 1994 ; 35 : 19 – 24.
Rumack CM et al. Diagnostic Ultrasound. Elsevier-Mosby, St. Louis, USA, 3rd edition, 2005.
Multilocular
Unilocular
Cystic necrosis
Origin in wall of
simple cyst
13. CECT
Enhancing soft-tissue
components within cyst
Cystic RCC
Adilson P et al. RadioGraphics 2006 ; 26 : 233 – 244.
Cystic mass with several
solid nodular components
US of right kidney
Complicated renal cyst
Bosniak category IV cyst
14. Multilocular cystic nephroma (MLCN)
Benign nonhereditary cystic neoplasm
• Multiple epithelially lined not communicating cysts
Benign neoplasm usually, metastases have been reported
• Bimodal presentation Males younger than 2 years
Women during 5th – 8th decades
• US:mass containing multiple cysts or internal septations
Not possible to distinguish from multiloculated RCC
Both are usually surgical lesions
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
15. Multilocular cystic nephroma (MLCN)
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
Predominantly cystic mass
Multiple internal septations
Longitudinal US
Better representation of lesion's
internal architecture at US
CECT scan
16. Multilocular cystic nephroma
Multiloculated RCC
Findings suggestive of MLCN
Absence of intratumoral or perinephric bleeding at CT or MRI
Herniation of portion of mass into renal pelvis
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
17. Renal sinus cyst
Common (1.5 % in autopsy series)
• Lymphatic in origin or develop from embryologic rests
• Do not communicate with collecting system
• Manifestations Most asymptomatic
Infection, bleeding, HTN, hydronephrosis
• Two patterns Parapelvic: single cyst in sinus & parenchyma
Peripelvic: multiple confluent cysts in sinus
The term renal sinus cyst recommended as generic
description of any fluid-filled cyst found in renal sinus
Rha SE et al. RadioGraphics 2004 ; 24 : S117 – S131.
18. Renal sinus cysts
Do not communicate with collecting system
Multiple renal sinus cysts
Mimic hydronephrosis
IVP, CECT, or MRI may be needed
Rumack CM et al. Diagnostic Ultrasound. Elsevier-Mosby, St. Louis, USA, 3rd edition, 2005.
Single renal sinus cyst
Simple cyst located in
renal sinus area
19. Ureteropelvic junction obstruction
Bilateral in one fourth of children
Severe UPJ obstruction
Dilated calyces as large cysts
Symmetrical in size
Communicate by sonography
Diminished renal parenchyma
UPJ obstruction
Dilatated intrarenal collecting system
Right ureter not dilated
Consistent with UPJ obstruction
Sivit CJ. Ultrasound Clin 2006 ; 1 : 67 – 75.
20. Cyst puncture
• Helpful in cases considered to be infected cyst or abscess
• Rarely use for management decision about cystic masses
Negative biopsy result does not rule out malignancy
Evaluation portion of lesion may result in misdiagnosis
• Complications: Tumor spread along needle track
Rupture
Bleeding
Infection
Hartman DS et al. RadioGraphics 2004; 24 : S101 – S115.
22. Autosomal dominant polycystic kidney disease
ADPKD
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
15.6 cm
Cysts of variable size with bilaterally enlarged kidneys
Compression of central sinus echo complex
Nephrolithiasis (20 – 35 % of patients)
Hepatic, pancreatic, ovarian, splenic, arachnoid, & other cysts
23. Differentiation simple cortical cysts from ADPKD
• Multiple cysts
At least 2 in each kidney after 30 years of age
CT shows multiple smaller cysts not visible on US
Distinction difficult in elderly: multiple cortical cysts
• Family history of ADPKD
• Coexistence of cysts in other organs
• Gene markers for ADPKD
McGahan J et al. Diagnostic ultrasound, Informa Healthcare, 2nd edition, 2008.
24. Screening of ADPKD
Renal US & DNA analysis in 319 patients at risk
Ravine D et all. Lancet 1994 ; 343 : 824 – 827.
Nicolau C et al. Radiology 1999 ; 213 : 273 – 276.
Person at risk & younger than 30 years
Two cysts in one kidney or one cyst in each kidney
Person at risk & aged 30 – 59 years
Two cysts in each kidney
Person at risk & aged 60 years or older
Four cysts in each kidney
Sen: 95% (ADPKD-1) – 65% (ADPKD-2)
(Sen: 100%)
(Sen: 100%)
26. Autosomal recessive polycystic kidney disease
ARPKD
• Varying degrees of renal failure & portal hypertension
• Severe form After birth – renal disease predominates
Neonatal US Kidneys enlarged bilaterally
Oligohydramnios
Potter’s facies
Pulmonary complications
• Later presentation Renal impairment & complications of CHF
Ultrasound Kidneys maintain reniform shape
Bilaterally enlarged & echogenic
27. ARPKD
Right kidney
10 cm in length
Bilaterally enlarged echogenic kidneys in a newborn
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
Left kidney
9.8 cm in length
28. von Hippel-Lindau disease
Rare disease (prevalence 1/ 35.000 – 40.000)
• Autosomal dominant disease with high penetrance
• Development of variety of benign & malignant tumors
• Broad clinical manifestations: 40 lesions in 14 organs
• Diagnostic criteria
More than one CNS hemangioblastoma
One CNS hemangioblastoma & visceral manifestations
Any manifestation & familial history of VHL disease
32. Leung RS et al.. RadioGraphics 2008 ; 28 : 65 – 79.
Multiple lesions of mixed echotexture
Multiple RCCs
von Hippel-Lindau disease (VHL)
Renal cell carcinoma (25 – 45%)
Sagittal US of left kidney CECT scan
Simple cysts
Solid enhancing lesions
Right nephrectomy (RCCs)
CBD stent (pancreatic cysts)
33. Leung RS et al.. RadioGraphics 2008 ; 28 : 65 – 79.
Multiple lesions of mixed echotexture
Multiple RCCs
von Hippel-Lindau disease (VHL)
Renal cell carcinoma (25 – 45%)
Sagittal US of left kidney CECT scan
Simple cysts
Solid enhancing lesions
Right nephrectomy (RCCs)
CBD stent (pancreatic cysts)
34. Screening protocol for VHL disease
Body System Regimen Follow-up
Renal Annual abdominal US from 10 y CT or MR
Depending on US findings
CNS MRI of brain & spine at 20 y
Annual neurologic exam if symptoms
Repeat imaging if suspicion
Adrenal Annual 24-h urinary VMA from 10 y
Annual blood pressure measurement
Imaging if VMA abnormal
Ophthalmic Annual ophthalmoscopy from 5 y
With or without fluorescein
–
Auditory Questionnaire
Audiogram if questionnaire positive
MRI If audiogram abnormal
Leung RS et al.. RadioGraphics 2008 ; 28 : 65 – 79.
38. Renal cysts seen in cortex & medulla
Appear at an earlier age than cysts seen in APKD
Tuberous sclerosis / Multiple renal cysts
Weber TM. Ultrasound Clin 2006 ; 1 : 15 – 24.
Not primary diagnostic feature
39. Angiomyolipoma – Classic pattern
Paspulati RM et al. Ultrasound Clin 2006 ; 1 : 25 – 41.
CT (excretory phase)
Fat attenuation lesion
Household unit of – 8
Well defined hyperechoic mass
Posterior acoustic shadowing
Longitudinal US of right kidney
Intratumoral fat on CT almost confirms diagnosis of AML
40. Renal intratumoral fat attenuation
Logue LG et al. RadioGraphics 2003; 23:241–246
Almost pathognomonic for AML
Rare benign & malignant tumors considered
• Renal cell carcinoma
• Lipoma & liposarcoma
• Myolipoma
• Oncocytoma
• Wilms tumor
41. Acquired cystic disease
Bates J A. Abdominal Ultrasound: How, Why and When.
Churchill Livingstone, Edinburg, UK, 2nd edition, 2004
Patients on long-term dialysis (shrunken end-stage kidneys)
Frequency increases with duration of dialysis
Potential for malignancy: screen native kidneys even after RT
42. Multicystic Dysplastic Kidney (MCDK)
• Complete early ureteral obstruction (< 8th – 10th week)
Incomplete ureteral obstruction later (10th – 36th week)
• Contralateral renal anomalies:
Most commonly UPJ obstruction in 33% of patients
• US Large non communicating cysts
Absence of identifiable cortical parenchyma
Absence of central sinus structures
• Calcify or not identifiable in few patients on follow-up
43. Multicystic dysplastic kidney (MCDK)
Renal dysplasia
Longitudinal view Transverse view
Sivit CJ. Ultrasound Clin 2006 ; 1 : 67 – 75.
Multiple parenchymal cysts of varying size
Cysts do not communicate
Absence of identifiable cortical parenchyma
Absence of central sinus structures
They are extremely common, the frequency increasing with age. They occasionally reach a considerable size of more than 10 cm, although they are usually 4 cm or less.Although cortical, they may be peripheral, extend from the surface of the kidney, or lie centrally, originating in the columns of Bertin. They often are multiple, particularly in the elderly, and when they are numerous, it is difficult to distinguish multiple cortical cysts fromautosomal dominant polycystic kidney disease (ADPKD).
Radiologic features that favor renal cell carcinomaPresence of blood in the tumor or in the perinephric space at CT or MR imagingRelatively large solid areas within the tumor mass, intravascular extension, or distant metastases. Findings suggestive of multilocular cystic nephromaAbsence of intratumoral or perinephric hemorrhageHerniation of a portion of the mass into the renal pelvis.
Also known as peripelvic cysts, parapelvic lymphatic cysts, parapelviclymphangiectasia, and parapelvic cyst.RSCs are likely lymphatic in origin or develop from embryologic rests.These cysts do not communicate with the collecting system.Most RSCs are asymptomatic, but they may become infected or bleed, and may cause hematuria, hypertension, or hydronephrosis
Multiple underlying factors have been proposed including:1- Abnormal development of the proximal ureteral smooth muscle2- Aberrant vessels, or bands crossing the upper ureter and renal pelvis3- Delayed recanalization of the fetal ureter4- Abnormal ureteral peristalsis.The ipsilateralureter is typically not dilated in children who have a UPJ obstruction, although ureteralvesical junction (UVJ) may occasionally coexist and result in a dilated ureter.
Parfrey PS et al. N Engl J Med 1990 ; 323 : 1085 – 90.US, because of high sensitivity and low cost, has become the primary method of diagnosing ADPKD and following the cysts.US screening for ADPKD typically begins between ages 10 & 15 years, (false negatives in 14% of patients younger than 30 years). Bear and colleagues developed criteria that are widely used to diagnose ADPKD. In adults who have a family history of ADPKD, the presence of at least three cysts in both kidneys, with at least one cyst in each kidney, is a positive finding.
Renal US & DNA analysis for ADPKD were performed in 319 patients who were at risk. PKD1: short arm of chromosome 16 – Account for 85 – 90 % of population with ADPKD.PKD2: Long arm of chromosome 4 – Account for 10 – 15% of population with ADPKD.In some other families, no linkage to either PKD1 or PKD2 has been reported.
No increased risk for RCC in patients who have ADPKD, except for: 1- Increased risk related to dialysis2- Generally increased risk for RCC in men
If TS is a consideration, the diagnosis can usually be confirmed on CNS imaging with subependymalhamartomasor giant cell astrocytomas.Multiple renal AMLs are a primary diagnostic feature of TS.Renal cysts are not the primary diagnostic feature of TS.
Tuberous sclerosis (Bourneville disease) is a phacomatosis, classically described as the triad of adenoma sebaceum, seizures, and mental retardation. The inheritance is autosomal dominant.
If TS is a consideration, the diagnosis can usually be confirmed on CNS imaging with subependymalhamartomas or giant cell astrocytomas. Presence of subependymal nodules and giant cell astrocytoma are sine qua non of TS.
Small RCCs can be hyperechoic and indistinguishable from an AML on sonography. Hypoechoic rim and intratumoral cystic changes are seen only in RCC, whereas acoustic shadowing is observed with AML.Rarely, RCCs can demonstrate fat attenuation caused by entrapment of the perinal or renal sinus fat, lipid necrosis, or osseous metaplasia. The characteristic intratumoral fat cannot be detected in 4.5% of AMLs. This finding has been attributed to minimal fat content or immature fat. These AMLs with low fat content demonstrate homogeneous and prolonged enhancement on a contrast enhanced scan, which distinguishes them from an RCC.
perirenal fat entrapment, lipid necrosis, or osseous metaplasia, all of which may occur in renal cell carcinoma