Bosniak Classification and Renal Cystic Disease " from both urological and radiological points of view " historical point of view , uses and diagnostic significance , accuracy , all of these points and more in this presentation :)

1. Bosniak Classification
& Renal Cystic Disease
By /
Shehab Emad
Resident Doctor at Urology Department
Qena University Hospital

2. Introduction
 Renal cysts are a common finding on routine radiological
studies. As such, patients are often referred to urologists for
their opinion regarding potential intervention and follow-up.
 Renal cysts, in general, may be classified as “simple” or
“complex.” “Simple” cysts are best defined using
sonographic criteria. These include :
1. Absence of internal echoes
2. Round / oval shape
3. Sharp , thin posterior walls
When all of the criteria met , the cyst is benign and no follow
up is required .
The difficulty arises when cysts don’t meet the rigid criteria of
“simple” definition .

3. Ultrasonographic picture of simple
cyst

4. Historic points
 In 1983, using early computed tomography (CT) scan technology,
renal cysts were discovered in 33% of patients in the same age
group.
 The Bosniak renal cyst classification system was initially reported in
1986, using CT scan findings.
 the Bosniak classification has been widely adopted and accepted
because it addresses a difficult clinical problem and is easy to apply
by both radiologists and Urologists.
 The original classification has divided renal cystic disease into IV
categories .
 However, It is usually easy to differentiate between lesions at the
ends of the spectrum,i.e. the benign simple cysts (Bosniak I) and
the clearly malignant Bosniak IV lesions as Simple cysts and solid
tumours are usually straightforward to diagnose, but
differentiating between complex renal cysts and cystic renal
tumours can be difficult. There is a narrow margin between
performing unnecessary surgery and missing a cancer.

5. Bosniak
IIF
After the original
classification was
described, it became
obvious that some
revision was in order
because there were
some category II
cysts that were
slightly more
complicated than
most category II
lesions but not
complicated enough to
place in category III.
For that reason, a
category IIF (F for
follow-up) was
introduced in 1993

6. Bosniak Classification

8. Bosniak Classification Accuracy
 Only a few studies have correlated cyst
classification using the Bosniak system with
histological findings after removal of kidneys at
surgery. Thus there is a lack of evidence to support
the classification’s ability to distinguish between
benign and malignant masses.
 One of these studies carried out on 82 cystic renal
masses were resected from 77 patients (Five
patients had two lesions evaluated.)
 Those patients were evaluated prospectively
according to Bosniak system , then underwent
surgery and resected masses were sent for
histopathology .

9. Bosniak Classification of Cystic Renal Masses
and Surgical Outcome of 82 lesions from 77
patients
MalignantBenignNO.category
044I
01111II
292049III
18018IV
473582Total

10. Interpretation of the study as regard proven
malignant risk in each category
TotalCategory
IV
Category
III
Category
II
Category
I
study
8218/18
(100%)
29/49
(59%)
0/11
(0 %)
0/4
(0 %)
Proven
malignant
risk

11. Management of renal cystic disease according to
Bosniak Classification
Managementcategory
Ignore & No need for follow upI , II
Follow upII F
Surgical excisionIII , IV

12. Guidelines for follow up in Bosniak
Classification IIF
 There are no national or international guidelines which
stipulate for how long a patient with a Bosniak IIF lesion
should undergo radiological surveillance
 Literature has been provided to support the view that
these patients should undergo surveillance for 5 years.
 The suggested policy is “the minimum follow up policy”
which is the policy to follow Bosniak IIF Renal
cysts by CT scans at 6 months, and 1 year, and
then annually until 5 years
 This policy may be varied to take into account the
age and comorbidity of the patient

13. Malignant risk in Bosniak IIF Lesions
 There have been differing views on this in the literatures
.
 Some report that the malignancy risk is 12 % , others
says that malignancy risk reach 20 % .
 However , some authors believe that the malignancy risk
of Bosniak IIF similar to Bosniak II !!!

14. Imaging modalities in following up Bosniak
IIF
 According to Bosniak IIF cysts are potentially
malignant and should be followed with CT
examinations, performed to determine
whether the cystic lesions change over time
with regard to morphology and contrast
enhancement pattern, subsequently resulting
in an up- or downgrading.
 Alternative imaging modalities includes a
combination of ultra-sound and MRI in the
follow-up for Bosniak IIF and reduces the
lifetime radiation dose (once the lesion has
been characterized by triphasic CT scan)
especially, in patients younger than 50 years.

16. Prerequests for Bosniak Classification
1. Both unenhanced and contrast-enhanced thin-section CT scans should
be obtained.
2. sections must be less than half the diameter of the lesion to allow
adequate assessment (ideally < 5mm)
3. an adequate bolus of contrast material (at least 100 mL of a contrast
agent) and at a rate of 2-3 ml/sec.
4. Timing of image acquisition is also critical. The contrast-enhanced
images should be obtained in uniform nephrographic phases
approximately 100 sec after the start of injection. Images obtained in
the earlier corticomedullary differentiation phase may obscure the
lesion or provide misleading information.
5. In the event of incidental discovery of a homogeneously high-
attenuation renal mass in patients in whom no preliminary unenhanced
scanning was performed, a delayed scan at 15 min may provide
sufficient information to distinguish between a benign high-density cyst
and a neoplasm. Deenhancement of the lesion suggests vascularity and
the likelihood of neoplasm, whereas unchanging high attenuation is
consistent with a high-density avascular cyst.

17. CT Vs MRI in Bosniak System
CT scan
The gold standard imaging
modality used till now .
MRI Some studies carry out advantages
of MRI over CT in the form of :
1. MRI can be helpful with
increasingly complex cyst
identification. Recent
developments with MRI scanning
allow shorter breath holds and
increased contrast resolution.
2. As such, the cysts may be
characterized in greater detail,
compared with CT scan.
3. The MRI may demonstrate poorly
identified septa on CT scan and
show enhancements that are not
otherwise clearly perceived.
4. Also, MRI may differentiate
between hemorrhagic cysts and
solid enhancing masses.

18. CT Vs MRI
Allogram compares
between CT & MRI
as regard specificity
& sensitivity in
differentiation
between surgical
and non-surgical
Renal Cystic
lesions using
Bosniak System .
Solid line  MSCT
Dotted line  MRI

19. Who is he
??
Morton A Bosniak
Clinical Professor;
Professor Emeritus
of Radiology
Department of
Radiology ,
NYU Radiology
Associates