Bosniak classification system of renal cystic masses (version 2005)
Citation, DOI, disclosures and article data
At the time the article was created Frank Gaillard had no recorded disclosures.
View Frank Gaillard's current disclosuresAt the time the article was last revised Calum Worsley had no financial relationships to ineligible companies to disclose.
View Calum Worsley's current disclosures- Bosniak classification system of renal cysts
- Bosniak renal cyst classification system
- Bosniak renal cyst classification
- Bosniak classification system of renal cystic lesions
- Current Bosniak classification (CBC)
The Bosniak classification system of renal cystic masses divides renal cystic masses into five categories based on imaging characteristics on contrast-enhanced CT. It helps predict a risk of malignancy and suggests either follow up or treatment.
On this page:
Images:
Usage
The Bosniak classification is widely used by radiologists and urologists for assessing renal cysts 3. It was last updated in 2005 12. A Bosniak classification, version 2019 11 has been proposed to increase the accuracy and include MRI features but does not yet (2022) have widespread validation.
Although practised by some, the use of ultrasonography to characterize the Bosniak classification remains controversial. Originally, it was felt that ultrasound was inadequate for the task as it was incapable of showing neovascularization (cf. contrast-enhanced CT/MRI), however, newer studies looking at contrast-enhanced ultrasound, suggest that this impediment is no longer true. There is also evidence that ultrasound has a higher sensitivity for intralesional septa than either CT or MRI 8,13.
ADVERTISEMENT: Supporters see fewer/no ads
Classification
The "official" Bosniak classification uses Roman numerals, not Arabic ones, for each category. The use of the term "grade", "stage", "group", "type", or similar for each category is technically incorrect. Version 2019 has switched from "category" to "class" 11.
Bosniak I
-
benign simple cyst
hairline-thin wall of ≤2 mm
water density
no septa, calcifications, or solid components
no enhancement
work-up: none
percentage malignant: ~0% 17
Bosniak II
-
benign cyst - "minimally complex"
few hairlines thin <1 mm septa or thin calcifications (thickness not measurable)
perceived enhancement
non-enhancing high-attenuation (due to proteinaceous or hemorrhagic contents) renal lesions <3 cm
generally well marginated
work-up: none
percentage malignant: ~0-6% 17,18
Bosniak IIF
-
minimally complex
multiple hairline thin septa or minimally smooth thickened walls or septa
perceived but no measurable enhancement of wall or septa
calcification can be present and may be thick and nodular
generally well marginated
high-attenuation lesion >3 cm diameter, totally intrarenal (<25% of wall visible); no enhancement
requiring follow-up (F for follow-up): needs ultrasound/CT/MRI follow up - no strict rules on the time frame but reasonable at 6 months, 12 months, then annually for 5 years 3
percentage malignant: ~5-26% 6,19-21
Bosniak III
-
indeterminate cystic mass
thickened irregular or smooth walls or septa with measurable enhancement
treatment/work-up: partial nephrectomy or radiofrequency ablation in poor surgical candidates 23,24
percentage malignant: ~55-72% 6,17,19,22
Bosniak IV
-
clearly malignant cystic mass
Bosniak III criteria + enhancing soft tissue components adjacent to but independent of wall or septum
treatment: partial or total nephrectomy
percentage malignant: ~91-100% 19,22
ADVERTISEMENT: Supporters see fewer/no ads
History and etymology
The Bosniak classification is named after Morton A Bosniak (1929-2016), who was professor emeritus in radiology at New York University (NYU) Langone School of Medicine. It was first published in 1986, introducing the 2F category in 1993, and revisions in 1997, 2005 and 2019 9,10,14-16.
Quiz questions
References
- 1. Israel GM, Bosniak MA. How I do it: evaluating renal masses. Radiology. 2005;236 (2): 441-50. doi:10.1148/radiol.2362040218 - Pubmed citation
- 2. Curry NS, Cochran ST, Bissada NK. Cystic renal masses: accurate Bosniak classification requires adequate renal CT. AJR Am J Roentgenol. 2000;175 (2): 339-42. AJR Am J Roentgenol (full text) - Pubmed citation
- 3. Warren KS, Mcfarlane J. The Bosniak classification of renal cystic masses. BJU Int. 2005;95 (7): 939-42. doi:10.1111/j.1464-410X.2005.05442.x - Pubmed citation
- 4. Park BK, Kim B, Kim SH et-al. Assessment of cystic renal masses based on Bosniak classification: comparison of CT and contrast-enhanced US. Eur J Radiol. 2007;61 (2): 310-4. doi:10.1016/j.ejrad.2006.10.004 - Pubmed citation
- 5. Israel GM, Bosniak MA. Follow-up CT of moderately complex cystic lesions of the kidney (Bosniak category IIF). AJR Am J Roentgenol. 2003;181 (3): 627-33. AJR Am J Roentgenol (full text) - Pubmed citation
- 6. Smith AD, Remer EM, Cox KL et-al. Bosniak category IIF and III cystic renal lesions: outcomes and associations. Radiology. 2012;262 (1): 152-60. doi:10.1148/radiol.11110888 - Pubmed citation
- 7. Escudier B, Eisen T, Porta C et-al. Renal cell carcinoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann. Oncol. 2012;23 Suppl 7 (suppl 7): vii65-71. doi:10.1093/annonc/mds227 - Pubmed citation
- 8. Muglia VF, Westphalen AC. Bosniak classification for complex renal cysts: history and critical analysis. Radiologia brasileira. 47 (6): 368-73. doi:10.1590/0100-3984.2013.1797 - Pubmed
- 9. Bosniak MA. The Bosniak renal cyst classification: 25 years later. Radiology. 262 (3): 781-5. doi:10.1148/radiol.11111595 - Pubmed
- 10. Megibow AJ, Israel GM. Morton A. Bosniak, MD. Radiology. 282 (2): 616. doi:10.1148/radiol.2016164037 - Pubmed
- 11. Silverman SG, Pedrosa I, Ellis JH, Hindman NM, Schieda N, Smith AD, Remer EM, Shinagare AB, Curci NE, Raman SS, Wells SA, Kaffenberger SD, Wang ZJ, Chandarana H, Davenport MS. Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment. (2019) Radiology. 292 (2): 475-488. doi:10.1148/radiol.2019182646 - Pubmed
- 12. Israel GM, Bosniak MA. An update of the Bosniak renal cyst classification system. (2005) Urology. 66 (3): 484-8. doi:10.1016/j.urology.2005.04.003 - Pubmed
- 13. Park BK, Kim B, Kim SH, Ko K, Lee HM, Choi HY. Assessment of cystic renal masses based on Bosniak classification: comparison of CT and contrast-enhanced US. (2007) European journal of radiology. 61 (2): 310-4. doi:10.1016/j.ejrad.2006.10.004 - Pubmed
- 14. Bosniak M. Diagnosis and Management of Patients with Complicated Cystic Lesions of the Kidney. AJR Am J Roentgenol. 1997;169(3):819-21. doi:10.2214/ajr.169.3.9275903 - Pubmed
- 15. Bosniak M. The Current Radiological Approach to Renal Cysts. Radiology. 1986;158(1):1-10. doi:10.1148/radiology.158.1.3510019 - Pubmed
- 16. Bosniak M. Problems in the Radiologic Diagnosis of Renal Parenchymal Tumors. Urol Clin North Am. 1993;20(2):217-30. - Pubmed
- 17. Sevcenco S, Spick C, Helbich T et al. Malignancy Rates and Diagnostic Performance of the Bosniak Classification for the Diagnosis of Cystic Renal Lesions in Computed Tomography - a Systematic Review and Meta-Analysis. Eur Radiol. 2017;27(6):2239-47. doi:10.1007/s00330-016-4631-9 - Pubmed
- 18. Wang S, Gu Y, Wolff N et al. Bap1 is Essential for Kidney Function and Cooperates with Vhl in Renal Tumorigenesis. Proc Natl Acad Sci U S A. 2014;111(46):16538-43. doi:10.1073/pnas.1414789111 - Pubmed
- 19. Schoots I, Zaccai K, Hunink M, Verhagen P. Bosniak Classification for Complex Renal Cysts Reevaluated: A Systematic Review. J Urol. 2017;198(1):12-21. doi:10.1016/j.juro.2016.09.160 - Pubmed
- 20. Smith A, Carson J, Sirous R et al. Active Surveillance Versus Nephron-Sparing Surgery for a Bosniak IIF or III Renal Cyst: A Cost-Effectiveness Analysis. AJR Am J Roentgenol. 2019;212(4):830-8. doi:10.2214/ajr.18.20415 - Pubmed
- 21. Hindman N, Hecht E, Bosniak M. Follow-Up for Bosniak Category 2F Cystic Renal Lesions. Radiology. 2014;272(3):757-66. doi:10.1148/radiol.14122908 - Pubmed
- 22. Mousessian P, Yamauchi F, Mussi T, Baroni R. Malignancy Rate, Histologic Grade, and Progression of Bosniak Category III and IV Complex Renal Cystic Lesions. AJR Am J Roentgenol. 2017;209(6):1285-90. doi:10.2214/ajr.17.18142 - Pubmed
- 23. Allen B, Chen M, Childs D, Zagoria R. Imaging-Guided Radiofrequency Ablation of Cystic Renal Neoplasms. AJR Am J Roentgenol. 2013;200(6):1365-9. doi:10.2214/ajr.12.9336 - Pubmed
- 24. Aoun H, Littrup P, Jaber M et al. Percutaneous Cryoablation of Renal Tumors: Is It Time for a New Paradigm Shift? J Vasc Interv Radiol. 2017;28(10):1363-70. doi:10.1016/j.jvir.2017.07.013 - Pubmed
Incoming Links
- Simple renal cyst
- Renal cyst - Bosniak class II
- Renal cysts
- Diffuse hepatic steatosis with renal cortical cyst
- Laparoscopic port site hernia with small bowel obstruction
- Synchronous ipsilateral pRCC of the kidney and TCC of the renal pelvis
- Intrahepatic artery aneurysm
- Multiple ureterolithiasis
- Amorphous Bosniak 1 renal cyst (CEUS)
- Crossed fused renal ectopia
- Multilocular cystic renal neoplasm of low malignant potential
- Cystic renal cell carcinoma
- Apple core sign (colon)
- Multilocular cystic renal neoplasm of low malignant potential
- Urinary bladder transitional cell carcinoma
- Multilocular cystic renal neoplasm of low malignant potential
- Bilateral sporadic synchronous clear cell renal cell carcinoma
- Multilocular cystic renal neoplasm of low malignant potential
- Renal cyst - Bosniak type IIF (CEUS)
- Renal cyst - Bosniak type II (CEUS)
Related articles: Pathology: Genitourinary
- obstetrics
-
first trimester
- ultrasound findings in early pregnancy
- embryo/fetus
- beta-hCG levels
- confirming intrauterine gestation
- pregnancy of unknown location (PUL)
- first trimester vaginal bleeding
- early structural scan
- aneuploidy testing
-
second trimester
- fetal biometry
- amniotic fluid volume
- fetal morphology assessment
- soft markers
- amnioreduction
- Doppler ultrasound
- nuchal translucency
- 11-13 weeks antenatal scan
- chorionic villus sampling (CVS) and amniocentesis
- other
- placenta
- placental anatomy
- placental developmental abnormalities
- placenta previa
- spectrum of abnormal placental villous adherence
- abnormalities of cord insertion
- abruptio placentae
- placental pathology
- vascular pathologies of placenta
- placental infections
- placental masses
- molar pregnancy
- twin placenta
- miscellaneous
-
first trimester
- gynecology
- acute pelvic pain
- chronic pelvic pain
- uterus
- ovaries
- ovarian follicle
- ovarian torsion
- pelvic inflammatory disease
- ovarian cysts and masses
- paraovarian cyst
- polycystic ovaries
- ovarian hyperstimulation syndrome
- post-hysterectomy ovary
- cervix
- fallopian tube
- other
- male genital tract
- prostate gland
- transrectal ultrasound
- prostate tumors
- infections of the prostate
-
prostatitis
- acute bacterial prostatitis
-
chronic prostatitis
- chronic bacterial prostatitis
- chronic prostatitis and chronic pelvic pain syndrome (CPPS)
- asymptomatic inflammatory prostatitis
- granulomatous prostatitis
- emphysematous prostatitis
- prostatic abscess
-
prostatitis
- benign prostatic hypertrophy
- cystic lesions of the prostate
- prostatic calcification
- prostatic infarction
- testes
-
unilateral testicular lesion
- testicular torsion
- orchitis
- testicular trauma
-
germ cell tumors of the testis
- testicular seminoma
-
non seminomatous germ cell tumors
- mixed germ cell tumor
- yolk sac tumor (endodermal sinus tumor)
- embryonal cell carcinoma
- choriocarcinoma
- testicular teratoma
- testicular epidermoid (teratoma with ectodermal elements only)
- burned out testis tumor
- sex cord / stromal tumors of the testis
- testicular cyst
- testicular lymphoma
- bilateral testicular lesion
- paratesticular lesions
- epididymis
- other
- polyorchidism
- cryptorchidism
- tubular ectasia of the rete testis
- cystadenoma of the rete testis
- testicular sarcoidosis
- testicular tuberculosis
- spermatic cord
- fibrous pseudotumor of the scrotum
- scrotal leiomyosarcoma
- testicular adrenal rest tumors (TARTs)
- tunica vaginalis testis mesothelioma
- splenogonadal fusion
- testicular vasculitis
- abnormal testicular Doppler flow (differential)
-
unilateral testicular lesion
- penis
- prostate gland
- KUB
- kidneys
- normal renal anatomy
- hydronephrosis
- urolithiasis
- renal masses
- renal cystic disease
- renal infection
- vascular
- trauma
- ureter
- normal ureter anatomy
- ureteral stricture
- ureteral dilatation
- ureteral anomalies
- ureteral tumors
- ureteral trauma
- other
- bladder
- kidneys