The Bosniak 2019 classification defines a cystic renal mass as one in which <25% of the mass is composed of enhancing tissue in order to avoid an aggressive necrosed solid renal mass being termed Bosniak IV.
Bosniak I and Bosniak II masses that are characterized as benign may be described as “cysts” and the term “cystic renal mass” should be applied to Bosniak IIF, III and IV lesions.
One or more enhancing thick (≥ 4 mm width) or enhancing irregular (displaying ≤ 3-mm obtusely margined convex protrusion[s]) walls or septa.
Kyste Simple Et Complexe Du Rein. Classification Des Masses Rénales Kystiques
One or more enhancing nodules (≥ 4-mm convex protrusion with obtuse margins, or a convex protrusion of any size that has acute margins)
Portal venous scan of a cyst with mean HU of 25 in the anterior right Kidney. According to the new Bosniak criteria all cyst with HU
Bosniak I masses are universally considered to be benign, and although there are occasional case reports of malignancy being found in these lesions, this is thought to be due to incorrect scan technique or incorrect image interpretation leading to incorrectly assigning a Bosniak I grade.
Bosniak Category Iif And Iii Cystic Renal Lesions: Outcomes And Associations
Malignancy rates in Bosniak II lesions are <1% and may be as low a 0%. A caveat to this is in patients with Von Hippel Lindau syndrome, hereditary leiomyomatosis and other RCC syndromes where benign appearing cystic masses may still harbor malignancy and the application of the Bosniak system is not recommended.
The incidence of malignancy in Bosniak IIF lesions is reported between 0-38% likely owing to differences in subjective grading of imaging features as well as strong selection bias whereby only the more worrisome lesions are resected. However, lesions in which there is progression of features from IIF to category III or IV have a high rate of malignancy of 85%, comparable to lesions initially characterised as Bosniak IV.
Bosniak III lesions are considered indeterminate with around half being malignant. Current practice regarding resection or observation varies between institutions and depends heavily on lesion size, patient comorbidities and surgeon preference.
Bosniak Classification Of Cystic Renal Masses, Version 2019: An Update Proposal And Needs Assessment.
Bosniak IV lesions are found to be malignant in around 90% of cases and treatment is recommended in most cases if patient characteristics allow
Size and growth rate are not included in the updated classification. It is however likely that the smaller the lesion, the more likely it is to be benign. Growth rate and change of morphology do however play an important role in the surveillance of lesions.
It is important to include patients’ age, comorbidities, life expectancy, personal preferences and risk tolerance into the considerations to treat or observe.
Cancer Du Rein De L'adulte (ou Carcinome à Cellules Rénales
Lesions with a solid component of > 25% are likely necrotic solid masses. These necrotic solid masses, as opposed to cystic masses, have a less indolent behavior.
Lesions with abundant thick nodular calcifications on CT can mask enhancement. In these lesions MRI with subtraction is advised to rule out enhancing soft tissue components.
Hyperattenuating non-enhancing lesions larger than 3 cm and heterogeneous non-enhancing lesions on CT can also benefit from further evaluation with MRI to exclude enhancement before assigning a Bosniak category.
Profils Histologiques Et Corrélation Radio Histologique Des Kystes Rénaux Bosniak 3 Et 4 Opérés
As more than 25% of the mass is composed of solid tissue this likely represents a necrotic mass in stead of a cystic lesion.
4 or more septa are termed “many” and if enhancing are features of a 2F lesion (in the absence of more worrisome features)
In the left diagram there are 2 septa connecting two surfaces (Bosniak II), and in the right diagram there are 5 different septa, defined as Bosniak IIF.
Pdf] Limitations Of Ct Scanning In Bosniak Staging Of Renal Cystic Carcinoma
Prior versions of the Bosniak classification divided enhancement between “perceived” and measurable, and all masses in which an area of enhancement could be measured could only be categorised as Bosniak III or IV.
Enhancement can be unequivocally perceived when comparing non-contrast and contrast-enhanced images performed using the same acquisition technique or ‘measurable’ using conventionally sized regions of interest” (not pixel values).
Image T2W coronal image of a cyst with many septa in the left kidney. On the T1W fatsat after contrast, these septa show obvious enhancement in comparison to the pre-contrast sequence.
Ultrasound Based “ceus Bosniak”classification For Cystic Renal Lesions: An 8 Year Clinical Experience
Although there is still likely to be some inter observer variation in the measurement of enhancing septal and wall thickness, the new 2019 guidance provides values for thickness in each Bosniak category, replacing the prior descriptive classification of “minimally thickened” or “thickened”.
The distinction between irregularity of enhancing wall or septa and a nodule relates to the angle formed with the associated wall or septum and the thickness.
Enhancing areas which form acute angles with a wall or septum are considered nodules and are always categorized as Bosniak IV features.
Bosniak Classification Of Cystic Renal Masses, Version 2019: A Pictorial Guide To Clinical Use
If an area of obtuse angled thickening is present on both sides of a septum then the combined thickness on both sides of the septum should be measured, excluding the thickness of the underlying septum itself.
On contrast CT Bosniak I cyst are well defined with a thin (≤2mm) smooth wall and contain homogenous, simple fluid (-9 – 20 HU) and no septa or calcifications.
In the 2019 version of the Bosniak classification more types of lesions can be characterized as Bosniak II (see table) in an attempt to increase specificity and to reduce the need to image or treat likely benign lesions.
Pdf] Bosniak Classification Of Cystic Renal Masses, Version 2019: An Update Proposal And Needs Assessment.
Most incidental kidney lesions are detected on single phase portal venous studies. If these lesions are homogeneous and have a HU of 21-30, malignancy is highly unlikely and Bosniak II can be applied.
Masses that are evaluated with a renal specific contrast protocol and have a HU of > 20 and show no enhancement are also assigned Bosniak II.
All thin walled cystic masses with enhancing septa and/or any type of calcification can now be categorized as Bosniak II, as long as the septa are few (1-3) and thin (≤ 2mm).
Complex Renal Cysts (bosniak ≥iif): Interobserver Agreement, Progression And Malignancy Rates
Homogeneous masses with Houndsfield units of -9-20 or ≥70 on non-contrast CT, as well as lesions -too small to characterize- but otherwise homogeneous and low-attenuating, can be placed in the Bosniak II category.
Many masses are discovered incidentally on CT or MR examinations performed for other indications not using a dedicated renal imaging protocol. Despite this, many masses can be safely described as benign.
Well defined homogeneous masses seen on non-contrast CT measuring between -9 to 20 HU or >70 HU are highly likely to be benign cysts and can be ignored.
Bosniak Classification Of Renal Cysts (illustrations)
On contrast enhanced CT the adjacent enhancing renal parenchyma may increase measured density (pseudo enhancement) within benign cysts. Therefore, cystic masses measuring <30 HU in the portal venous phase are also considered benign.
On unenhanced MR, well defined homogeneous masses which are hyperintense on T1 (around 2.5x normal parenchymal intensity) or well defined masses with T2 signal intensity similar to CSF are considered benign.
Small masses may not be characterizable due to partial voluming if the slice thickness is more than half the diameter of the mass. In practice, pseudo enhancement can occur in masses up to 1.5cm in diameter and if these otherwise appear homogeneous they should be considered benign Bosniak II lesions.
Three Phase, Contrast Enhanced, Multidetector Ct In The Evaluation Of Complicated Renal Cysts: Comparison Of The Postcontrast Phase Combination
In the updated 2019 classification non-enhancing septa cannot be counted as such, and the lesion is therefore downgraded to a Bosniak II cyst.
Case 4 Small masses may not be characterizable due to partial voluming if the slice thickness is more than half the diameter of the mass.
A homogeneous, hypodense lesion is seen in the posterior right kidney. This lesion is too small to characterize and is classified as Bosniak II.
Diagnostic Performance Of Contrast‐enhanced Ultrasonography And Magnetic Resonance Imaging For The Assessment Of Complex Renal Cysts: A Prospective Study
On the non-enhanced CT (NECT) there is a hyperdense lesion in the left kidney with HU > 70, which would normally correspond to a Bosniak II lesion (white arrow). A contrast-enhanced CT (CECT) in the portovenous phase shows no significant contrast uptake but there is an inhomogeneous appearance.
Not much has changed in the IIF category, besides that the criteria are now more well defined. Cystic IIF masses have either more than a few (≥4 ) thin (≤2mm) septa or few (1-3) minimally thickened (3 mm) septa both on CT and on MRI.
Heterogeneous masses on CT without significant contrast enhancement should be considered as incompletely characterized. MRI is recommended to further asses these lesions before applying the Bosniak criteria.
Evaluation Of Bosniak Category Iif Complex Renal Cysts
This is the only mass type that is categorized greater than Bosniak II without enhancing features. The reasoning behind this is that papillary cancers can present with this finding.
According to the previous criteria, Bosniak III masses are ‘indeterminate’ with about half of the resected masses being benign, resulting in potential harm of treatment without clinical benefit.
In 2019 the criteria have been more clearly defined. Any cystic mass with one or more irregular septa or irregular enhancing wall of 3 mm or smooth thickened wall or septation of ≥4mm are considered Bosniak III.
Renal Cell Carcinoma
The term ‘irregular’ is defined as diffuse convex protrusions that have obtuse margins with the wall or septa (see section wall irregularity above).
MRI of an exophytic cortical cyst in the left kidney with few, irregular thickened (3 mm) septa with obtuse margins which enhance after contrast, in keeping with findings of a Bosniak III cyst.
Cystic masses with Bosniak IV characteristics are highly likely to be malignant (90%) and present with larger soft tissue components and thick enhancing irregular walls.
Bosniak Classification System Of Renal Cystic Masses
Nodules are defined as focal enhancing convex protrusions of any size with acute angles to the septa
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