Keywords
diverticulitis - diverticular disease - CDD - agreement - computed tomography
Introduction
Diverticular disease (DD) is a common, gradually progressive gastrointestinal disorder
with increasing prevalence [1]. DD usually manifests in early adulthood and progresses with advancing age with
respect to its anatomical extent and diverticula size. In western countries, up to
30 % of individuals are expected to develop asymptomatic diverticulosis by the age
of 50 years and 60–70 % by the age of 80 years [2]. While most people with colonic diverticulosis remain asymptomatic, it is estimated
that around 5–20 % will develop symptoms [3]
[4]. The clinical spectrum of symptomatic DD ranges from mild abdominal pain up to life-threatening
complications including perforation and hemorrhage [5]
[6]
[7].
Diverticulitis is diagnosed based on typical clinical symptoms (e. g., left lower
quadrant pain and fever) and elevated blood serum inflammatory parameters. In addition,
early radiologic imaging is recommended and used to establish the diagnosis [8]. Besides ultrasound, CT has become a mainstay in patients with suspected diverticulitis
due to its excellent sensitivity and specificity [9]
[10]. By means of CT, not only confirmation of DD is feasible, but also assessment of
disease stage including treatment stratification, and exclusion of important differential
diagnoses.
Exact classification of DD is required for stage-related therapy. In the past, various
staging systems have been endorsed by different national and international societies
[11]
[12]
[13]
[14]
[15]
[16]. Over time, algorithms for DD changed from primarily clinical and surgical to more
radiological-based classifications with respect to imaging features, thereby substantiating
the increasing impact of imaging. Introduced in 2014 and recently updated in the German
S3 guideline for Diverticular Disease and Diverticulitis (2021), the Classification
of Diverticular Disease (CDD) is used in German-speaking countries primarily with
respect to radiological imaging and diagnosis [8]
[17]. The main purpose of this new CDD classification was to establish a more comprehensive
and treatment-relevant categorization of separate stages of DD ([Table 1]). Recent studies have shown that the CDD enables reliable staging of disease severity
[9]
[18].
Table 1
Classification of Diverticular Disease (CDD).
Tab. 1 Klassifikation der Divertikelkrankheit (Classification of diverticular disease, CDD).
|
Term
|
Synonym
|
Definition
|
CDD
|
|
Asymptomatic diverticulosis
|
|
Identification of diverticula in colon
|
Type 0
|
|
Acute uncomplicated diverticulitis
|
Diverticulitis without perforation
|
Diverticulitis without peridiverticulitis
|
Type 1a
|
|
Diverticulitis with phlegmonous peridiverticulitis
|
Type 1b
|
|
Acute complicated diverticulitis
|
Diverticulitis with covered perforation
|
Microabscess (≤ 3 cm), minimal free paracolic air
|
Type 2a
|
|
Macroabscess (> 3 cm)
|
Type 2b
|
|
Free perforated diverticulitis
|
Free air, generalized peritonitis
|
Type 2c
|
|
Chronic diverticular disease
|
Symptomatic uncomplicated diverticular disease (SUDD)
|
Typical clinical features
|
Type 3a
|
|
Relapsing diverticulitis without complications
|
Recurrent signs of inflammation
|
Type 3b
|
|
Relapsing diverticulitis with complications
|
Identification of stenosis, fistulas, conglomerate tumor
|
Type 3c
|
|
Diverticular bleeding
|
|
Identification of source of bleeding
|
Type 4
|
As with all new staging systems, different aspects of clinical applicability in daily
radiological practice have to be examined. Therefore, the aim of our study was to
evaluate the intra- and interobserver agreement of the CDD classification in patients
undergoing abdominal CT for suspected symptomatic DD.
Materials and Methods
Patients
This retrospective study was approved by the local institutional review board with
a waiver of patient consent granted. In our study we used a pre-existing fully characterized
patient population in whom imaging was performed for suspected DD from a previous
study [9]. A composite endpoint of a consensus reading, intraoperative findings, and clinical
follow-up from that study served as the reference standard. In total, 481 abdominal
CT scans were evaluated. Inclusion criteria were as follows: age ≥ 18 years and surgical
or clinical follow-up of at least 4 weeks. Non-diagnostic CT scans were excluded.
Abdominal CT scans were acquired on a 64-slice (VCT) or 16-slice (LightSpeed) scanner
(both GE HealthCare). Depending on clinical context and contraindications, the CT
technique varied, including non-contrast or intravenous contrast-enhanced image acquisition
with or without additional oral or rectal contrast application (with rectal contrast
(G1): n = 99, without rectal contrast (G2): n = 382).
CT evaluation
Image analysis was performed by two radiologists independently of each other. To address
different levels of education, one board-certified radiologist with 6 years of experience
(reader A) and one 3rd year radiology resident (reader B) were recruited. Both readers were aware of the
clinical indication for imaging and the patients’ periods of diverticulitis in order
to allow classification of patients into CDD category 3 (chronic DD) but were otherwise
blinded to additional clinical data or possible follow-up imaging. In preparation,
both radiologists read 20 cases not included in this study together with a senior
radiologist in order to get familiar with the classification. Afterwards, both radiologists
individually evaluated all CT scans in two reading sessions, separated by a 3-month
period in order to minimize recall bias. Image evaluation was performed on a commercially
available workstation (Visage 7.1, Pro Medicus Inc) in axial, coronal, and sagittal
reformations. If DD was suspected on imaging, findings were classified using the CDD
according to the recently updated German S3 guideline for Diverticular Disease and
Diverticulitis (2021) [8] ([Table 1]).
Statistical analysis
Statistical analysis was performed using GraphPad Prism 9 (GraphPad Software Inc.).
Intraobserver agreement and interobserver agreement between reader A and B in both
reading sessions as well as between both readers and the consensus reference standard
for CDD stages were calculated using a (weighted) Cohen-k statistic. k-values were
interpreted as follows: a value less than 0.20 indicated poor agreement; a value between
0.21 and 0.40 fair agreement; a value between 0.41 and 0.60 moderate agreement; a
value between 0.61 and 0.80 substantial agreement; a value between 0.81 and 1.00 almost
perfect agreement [19]. To test for potential differences regarding the CDD categories between patients
with (G1) and without rectal contrast (G2), the Fisher’s exact test was used after
exclusion of a Gaussian distribution using Shapiro-Wilk. Being dependent on the (observational)
prevalence of the characteristic, comparison of different patient cohorts based on
Cohen’s kappa has only very limited validity [20]. Therefore, agreement between G1 and G2 was given as a percentage, and evaluation
of the interobserver agreement and the agreement with the reference standard was based
on the second reading session. For all measurements, p < 0.05 indicated a significant
difference.
Results
Based on consensus reading and clinical or histological/surgical findings as the reference,
DD of the colon was present in 317 (66 %) cases. The frequency of the categories according
to the CDD classification is given in [Table 2]. DD was mostly classified as CDD stage 0 in 28 % of cases (n = 88), stage 1b in
30 % (n = 97), and stage 2a in 14 % (n = 45). Of all 481 CT scans, DD was diagnosed
by reader A in 335 cases (70 %) and by reader B in 357 cases (74 %). DD was predominantly
diagnosed as stage 0 in 29 % and 25 % of cases, stage 1b in 18 % and 28 % and stage
2a in 19 % and 11 %, respectively. With regard to the CDD categories, there were no
statistically significant differences between patients who received rectal contrast
(G1) and those who did not (G2). However, there were more severe cases in the subgroup
with rectal contrast agent (CDD type 0: 19 % vs. 30 %, CDD type 1: 26 % vs. 34 %,
CDD type 2: 44 % vs. 30 %, CDD type 3: 11 % vs. 6 %).
Table 2
Frequency of diverticular disease (DD) categories according to the CDD.
Tab. 2 Häufigkeit der Kategorien der Divertikelkrankheit (DK) gemäß der CDD-Klassifikation.
|
CDD classification
|
Reference (G1/G2)
|
Reader A
|
Reader B
|
|
DD
|
317 (71/246)
|
335
|
357
|
|
0
|
88 (4/74)
|
96
|
88
|
|
1[*]
|
102
|
65
|
104
|
|
1a
|
5 (0/5)
|
4
|
3
|
|
1b
|
97 (19/78)
|
61
|
101
|
|
2*
|
106
|
96
|
79
|
|
2a
|
45 (14/31)
|
62
|
38
|
|
2b
|
31 (8/23)
|
30
|
25
|
|
2c
|
28 (8/20)
|
24
|
26
|
|
3a
|
0
|
0
|
0
|
|
3b
|
19 (6/13)
|
19
|
19
|
|
3c
|
4 (2/2)
|
0
|
0
|
|
4
|
0
|
0
|
0
|
G1: with rectal contrast; G2: without rectal contrast.
* Subgroups of CDD types 1 and 2 were combined to a common category.
Intraobserver agreement
Intraobserver agreement was almost perfect for both readers (reader A: 88.4 % agreement,
weighted kappa 0.93; reader B: 84.0 % agreement, weighted kappa 0.88) ([Table 3]). Disagreement was observed in n = 47 cases for Reader A and in n = 57 cases for
reader B, mostly related in CDD type 1b/2a (n = 16 and n = 14) and 1b/2b for reader
A (n = 11) and types 2a/2b and 1a/0 for reader B (n = 9 each). Discrepancy in DD severity
between the two reading sessions was slightly pronounced in the resident compared
to the board-certified radiologist. At subgroup analysis, agreement was substantial
to almost perfect for all CDD stages and both readers (mean kappa 0.73–1.00) except
for CDD type 1a (mean kappa 0.49, indicating moderate agreement). Of note, for CDD
stage 1a there was a significant difference between the intraobserver agreement of
the two readers (substantial versus fair agreement). Inconsistency between CDD category
1 (acute uncomplicated diverticulosis) and CDD category 2 (acute complicated diverticulosis)
was similar among the two observers (n = 27 for reader A and n = 20 for reader B).
When combining subgroups CDD types 1 and 2 in a single category, intraobserver agreement
was substantial for category 1 (mean kappa 0.77) and almost perfect for category 2
(mean kappa 0.83) for both readers.
Table 3
Intraobserver agreement of diverticular disease (DD) stages according to the CDD.
Tab. 3 Intraobserver-Übereinstimmung der Stadien der Divertikelkrankheit (DK) gemäß der
CDD-Klassifikation.
|
CDD
|
Reader A
|
Reader B
|
Mean
|
G1
|
G2
|
|
Kappa (95 % CI)
|
Kappa (95 % CI)
|
Kappa
|
Mean agreement (%)
|
Mean agreement (%)
|
|
Overall
|
0.93
|
0.88
|
0.91
|
86
|
88
|
|
0
|
0.99 (0.97–1.00)
|
0.85 (0.79–0.91)
|
0.92
|
85
|
87
|
|
1[*]
|
0.77 (0.69–0.85)
|
0.77 (0.71–0.84)
|
0.77
|
86
|
77
|
|
1a
|
0.72 (0.42–1.0)
|
0.26 (0.01–0.52)
|
0.49
|
50
|
23
|
|
1b
|
0.75 (0.66–0.83)
|
0.80 (0.73–0.86)
|
0.78
|
64
|
77
|
|
2[*]
|
0.82 (0.76–0.88)
|
0.84 (0.78–0.90)
|
0.83
|
89
|
85
|
|
2a
|
0.80 (0.72–0.88)
|
0.71 (0.61–0.82)
|
0.76
|
71
|
72
|
|
2b
|
0.73 (0.61–0.84)
|
0.72 (0.59–0.85)
|
0.73
|
70
|
67
|
|
2c
|
0.98 (0.94–0.10)
|
0.94 (0.87–1.00)
|
0.96
|
95
|
92
|
|
3b
|
1.00 (1.00–1.00)
|
0.97 (0.92–1.00)
|
0.99
|
100
|
100
|
G1: with rectal contrast; G2: without rectal contrast.
* Subgroups of CDD types 1 and 2 were combined to a common category.
The mean intraobserver agreement between the subgroups G1 and G2 was in total at a
comparably very high level (86 % and 88 % agreement). Except for CDD type 1a, which
seems to be negligible given only a small number of cases (G1 mean n = 2, G2 mean
n = 5), agreement was moderately better only for CDD type 1b in patients without rectal
contrast (77 % vs. 64 %).
Interobserver agreement
Interobserver agreement was substantial in reading session 1 (68.8 % agreement, kappa
0.77) and almost perfect in reading session 2 (75.6 % agreement, kappa 0.84) ([Table 4]). Except for CDD type 1a, an improvement from the first to the second reading session
could be observed for each subtype: significant improvement for CDD type 1b (moderate
vs. substantial agreement, kappa 0.58 to 0.70) and type 2b (fair vs. moderate agreement,
kappa 0.29 to 0.47).
Table 4
Interobserver agreement of diverticular disease (DD) stages according to the CDD.
Tab. 4 Interobserver-Übereinstimmung der Stadien der Divertikelkrankheit (DK) gemäß der
CDD-Klassifikation.
|
CDD
|
Session 1
|
Session 2
|
|
G1
|
G2
|
|
Kappa (95 % CI)
|
Kappa (95 % CI)
|
Mean Kappa
|
Agreement (%)
|
Agreement (%)
|
|
Overall
|
0.77
|
0.84
|
0.81
|
75
|
74
|
|
0
|
0.81 (0.74–0.88)
|
0.84 (0.78–0.91)
|
0.83
|
69
|
81
|
|
1[*]
|
0.55 (0.45–0.64)
|
0.67 (0.58–0.75)
|
0.63
|
52
|
64
|
|
1a
|
0.23 (–0.05–0.52)
|
0.11 (–0.12–0.33)
|
0.17
|
25
|
0
|
|
1b
|
0.58 (0.48–0.67)
|
0.70 (0.62–0.79)
|
0.64
|
59
|
66
|
|
2[*]
|
0.68 (0.60–0.76)
|
0.75 (0.68–0.83)
|
0.72
|
80
|
69
|
|
2a
|
0.43 (0.31–0.55)
|
0.50 (0.39–0.62)
|
0.47
|
48
|
32
|
|
2b
|
0.29 (0.13–0.44)
|
0.47 (0.32–0.63)
|
0.38
|
62
|
28
|
|
2c
|
0.83 (0.71–0.94)
|
0.88 (0.78–0.97)
|
0.86
|
70
|
84
|
|
3b
|
0.97 (0.92–1.00)
|
1.00 (1.00–1.00)
|
0.99
|
100
|
100
|
G1: with rectal contrast; G2: without rectal contrast.
* Subgroups of CDD types 1 and 2 were combined to a common category.
Classification according to the CDD by the two readers A and B was discrepant in 143
cases (30 %) in the first reading session and in 115 cases (24 %) in the second reading
session. In 86 cases, the disagreement was identical in both readings. In n = 41 (first
reading session) and n = 34 (second reading session), there was a discrepancy regarding
whether diverticulosis was present or not. In general, there was a tendency towards
higher CDD categories for reader A compared to reader B, mostly between CDD type 1b/2a
(first/second reading n = 28/24) and 2a/2b (n = 28/26). Representative examples of
differently classified cases of DD by readers A and B are presented in [Fig. 1]. In the subgroup analysis, the level of agreement was almost perfect for CDD types
0, 2c, and 3b (mean kappa: 0.83, 0.86, and 0.99, respectively) and substantial for
type 1b (mean kappa: 0.64). Less consensus was observed for CDD types 2a and 2b (moderate
and fair agreement, mean kappa: 0.47 and 0.38, respectively). The poorest agreement
was seen in CDD type 1a (slight agreement, kappa 0.17). When combining subgroups in
CDD type 1 (acute uncomplicated diverticulitis) and 2 (acute complicated diverticulitis)
in a single category, interobserver agreement was substantial and could be improved
from the first to the second reading session in both groups (category 1: mean kappa
0.63, category 2: mean kappa 0.72).
Fig. 1 CT image examples of interobserver disagreement. Different examples of interobserver
disagreement when applying the CDD classification are presented. Interpretation of
inflamed diverticulum vs. covered perforation (upper row), highly edematous intestinal
wall vs. perforated wall with mural abscess (middle row), and gas-filled diverticulum
vs. small neighboring free air bubble (lower row) can be challenging in some cases.
Abb. 1 Bildbeispiele der Interobserver-Unstimmigkeit in der Kategorisierung der Divertikelerkrankung.
Gezeigt sind verschiedene Fallbeispiele der Divertikelkrankheit, die von den Lesern
unterschiedlich kategorisiert wurden. Die Abgrenzung eines entzündeten Divertikels
gegenüber einer gedeckten Perforation (obere Reihe), einer stark ödematösen Darmwand
im Vergleich zu einer perforierten Wand mit intramuraler Abszedierung (mittlere Reihe),
oder eines luftgefüllten Divertikels gegenüber einer kleinen benachbarten freien Luftblase
(untere Reihe) kann in einigen Fällen schwierig sein.
The mean interobserver agreement in the G1 and G2 subgroups was in total equally high
(75 % and 74 % agreement). With rectal contrast, agreement between the two observers
was higher for complicated diverticulitis, especially for covered perforated diverticulitis
(CDD type 2a: 48 % vs. 32 %; CDD type 2b: 62 % vs. 28 %). However, the percentage
of discrepant classifications concerning CDD types 1 and 2 was not significantly different
with or without rectal contrast (G1: 38 % vs. G2: 42 % of all disagreements).
Acute complicated diverticulitis without free perforation (CDD type 2a/b)
In addition to the German S3 guideline for Diverticular Disease and Diverticulitis
recently updated in 2021 [8], we performed a modified analysis based on the initially proposed classification
as presented in the prior S2k guideline [17]. CDD types 2a and 2b represent covered perforated stages of diverticulitis and are
defined by the abscess size. In the newer S3 guideline, the abscess size threshold
has been increased from 1 cm to 3 cm to differentiate between a micro- and a macroabscess.
Applying the revised definition with a threshold of 3 cm resulted in downstaging from
CDD type 2b to CDD type 2a in 46–60 % of cases (reader A: n = 89 to n = 34, reader
B: n = 51 to n = 28). For both sizes, intraobserver agreement was substantial (kappa
0.74 and 0.78, respectively) with improvement for both readers compared to a 1 cm
threshold (reader A: kappa 0.80, 95 % CI [0.66–0.94] vs. kappa 0.84, 95 %, CI [0.73–0.96];
reader B: kappa 0.67, 95 % CI [0.49–0.86] vs. kappa 0.72, 95 % CI [0.58–0.90]). The
interobserver agreement for CDD types 2a and 2b was poor for both the 1 cm and 3 cm
threshold (fair agreement, mean kappa: 0.30 and 0.27, respectively).
Agreement between observers and reference standard
Agreement between observers and reference standard
In total, consensus in CDD categorization between the reference standard and reader
A was observed in n = 247 and 261 (mean agreement 81 %) and reader B in n = 229 and
239 (mean agreement 76 %), respectively. For both readers almost perfect agreement
was observed (mean kappa: 0.86 and 0.82, respectively) ([Table 5]). For reader B agreement improved from the first to the second reading session from
substantial to almost perfect. Poor consensus was observed for CDD type 1a for both
readers and limited agreement was observed for reader A for CDD type 1b (mean 65 %)
and for reader B in CDD types 2a and 2b (mean 48 % and 57 %).
Table 5
Agreement between observers and the reference standard.
Tab. 5 Übereinstimmung mit dem Referenzstandard.
|
|
0
|
1a
|
1b
|
2a
|
2b
|
2c
|
3b
|
3c
|
Kappa
|
|
Reference
|
88
|
5
|
97
|
45
|
31
|
28
|
19
|
4
|
|
|
Session 1
|
Reader A
|
82 (93 %)
|
1 (20 %)
|
61 (63 %)
|
36 (80 %)
|
24 (77 %)
|
24 (86 %)
|
18 (95 %)
|
0 (0 %)
|
0.85 (80 %)
|
|
Reader B
|
74 (84 %)
|
0 (0 %)
|
75 (77 %)
|
24 (53 %)
|
16 (52 %)
|
23 (82 %)
|
18 (95 %)
|
0 (0 %)
|
0.80 (76 %)
|
|
Mean
|
89 %
|
10 %
|
70 %
|
67 %
|
65 %
|
84 %
|
95 %
|
0 %
|
|
|
Session 2
|
Reader A
|
83 (94 %)
|
1 (20 %)
|
64 (66 %)
|
41 (91 %)
|
28 (90 %)
|
25 (89 %)
|
18 (95 %)
|
0 (0 %)
|
0.87 (84 %)
|
|
Reader B
|
81 (92 %)
|
0 (0 %)
|
76 (78 %)
|
19 (42 %)
|
19 (61 %)
|
25 (89 %)
|
18 (95 %)
|
0 (0 %)
|
0.83 (76 %)
|
|
Mean
|
93 %
|
10 %
|
72 %
|
67 %
|
76 %
|
89 %
|
95 %
|
0 %
|
|
|
G1
|
Reference
|
13
|
0
|
18
|
14
|
8
|
8
|
6
|
2
|
|
|
Mean
|
8 (92 %)
|
|
11 (61 %)
|
11 (78 %)
|
8 (100 %)
|
8 (100 %)
|
6 (100 %)
|
0 (0 %)
|
0.79 (75 %)
|
|
G2
|
Reference
|
74
|
5
|
78
|
31
|
23
|
20
|
13
|
2
|
|
|
Mean
|
69 (93 %)
|
1 (20 %)
|
59 (76 %)
|
21 (68 %)
|
11 (47 %)
|
17 (85 %)
|
12 (92 %)
|
0 (0 %)
|
0.84 (80 %)
|
Absolute numbers of agreement and percentage of reference for each CDD category are
given.G1: with rectal contrast; G2: without rectal contrast.
Consensus in CDD categorization was high, with or without rectal contrast (G1: mean
agreement 75 %, G2: mean agreement 80 %). In the group with rectal contrast, better
agreement could be observed for complicated diverticulitis (CDD category 2) compared
to patients without rectal contrast (93 % vs. 67 %). The percentage of discrepant
classifications concerning CDD types 1 and 2 was not significantly different (G1:
48 % vs. G2: 54 % of all disagreements).
Discussion
The Classification of Diverticular Disease is based on radiological findings, which
are linked to different, more unified treatment options, when compared with previously
published systems. Before any classification can be applied in practice, its reproducibility
should be put to the test and shown to be as robust as possible. To the best of our
knowledge, this is the first study evaluating the intra- and interobserver agreement
of the CDD classification in detail since its initial publication in 2014. In the
present study, we demonstrated that the CDD may be utilized with high intra- and interobserver
agreement, independent of the level of expertise of the radiologist reading the scans.
As mentioned in the introduction, there are different classifications for DD staging.
Ünlü et al. analyzed the interobserver agreement of CT stages of diverticulitis according
to the modified Hinchey, the Ambrosetti, and the Dharmarajan classification, which
are applied especially in the Anglo-American region [11]
[12]
[13]. The authors demonstrated a median overall interobserver agreement with kappa values
between 0.72 and 0.83 [21]. This is in line with our results assessing DD using the CDD classification, which
show an overall substantial to almost perfect interobserver agreement, even in the
case of different levels of experience. Interobserver agreement improved from the
first reading session to the second. Hence, we estimate that radiologist training
and level of experience may further improve the applicability of the CDD. This might
also be an explanation for the slightly lower intraobserver agreement of the less
experienced reader B compared to reader A, a board-certified radiologist. Nevertheless
and more importantly, even with less experience when first using the CDD classification,
substantial agreement with the reference could be achieved, similar to that of the
board-certified radiologist.
When analyzing the subtypes of the CDD categories, both intra- and interobserver agreement
was highest in CDD types 0 and 2c. Diverticula (type 0) and free abdominal air (type
2c) are radiological features that can be easily detected on CT scans. However, in
our study in a moderate number of cases there was an interobserver discrepancy regarding
whether or not diverticulosis was present. In almost all of these cases only a marginal
number of small diverticula were present. This seems negligible, as asymptomatic diverticulosis
does not require treatment. In contrast to these almost clear, objective radiological
features, visualization of wall thickening (CDD type 1a) may depend on dilatation
of the bowel and is interpreted in a more subjective way, especially in less severe
forms. In addition, it can be challenging to determine if small air bubbles next to
an air-filled diverticulum are outside or inside the intestinal lumen (CDD type 2a).
The interpretation of these findings may be more dependent on the radiologist’s experience
and could explain the poor interobserver agreement for the classification of CDD subtypes
1a and 2a. However, by combining the subtypes of CDD category 1 and category 2, acute
uncomplicated diverticulitis and acute complicated diverticulitis could be easily
discriminated from each other with high intra- as well as interobserver agreement.
This is important because both categories are related to different therapy strategies:
acute uncomplicated diverticulitis (CDD type 1) can be treated primary conservatively
and potentially on an outpatient basis, whereas patients with acute complicated diverticulitis
(CDD type 2) are usually managed on an inpatient basis, possibly including surgical
or interventional treatment [8]
[22].
As mentioned above, considering the reduced agreement of reader B (resident) with
the reference for CDD type 2, less obvious perforations and abscesses are probably
not as easy to diagnose as assumed. It has been postulated that enteric contrast administration
helps to distinguish intraluminal from extraluminal air and fluid collections [23]. This might be underlined by the tendency for better agreement in patients with
rectal contrast for perforated diverticulitis. However, the percentage of discrepant
classifications between CDD types 1 and 2 was similar and thus the therapy-relevant
differentiation between uncomplicated and complicated diverticulitis could not be
significantly improved with rectal contrast agent. This could be due to the fact that
the absence of extraintestinal findings does not exclude the possibility of a (covered)
alimentary tract perforation [24].
In the recently updated S3 guideline on CDD, an enlarged abscess size of 3 cm was
determined as a new threshold to discriminate between CDD stage 2a (microabscess)
and 2b (macroabscess). Our study showed that intraobserver agreement could be improved
using the 3 cm abscess size threshold. However, interobserver agreement was only fair
for both thresholds. In contrast to CDD categories 1 and 2, until now there is no
sufficient evidence for practical distinction between CDD subtypes 2a and 2b. In the
recently published bicentric observation study VADIS (Validation of the German Classification
of Diverticular Disease), Lauscher et al. validated the CDD classification and detected
a difference between patients with micro- and macroabscess regarding quality of life
and the need for surgery [25]. While patients with CDD type 2a could be treated conservatively on a long term
basis, all patients with CDD type 2b required surgery within 2 years of follow-up. Although
the redefined abscess size of 3 cm does not significantly improve the practical applicability
of the CDD classification from the radiological point of view, it reflects the practical
approach more accurately, e. g., therapeutic options like percutaneous drainage. Furthermore,
when correlating imaging findings in patients with CDD type 2b with intraoperative
findings, we found a slight tendency toward overstaging on CT, when the 1 cm threshold
was applied [9]. Hence, increasing the size of abscess definition seems to be a reasonable recommendation.
This study has potential limitations. First, CT image acquisition was not standardized
and, depending on additional clinical indications, a wide range of scan protocols
was used. However, despite being a frequent examination, until now there is no consensus
regarding the scan protocol, and consistent recommendations on how to perform CT examinations
in patients with suspected DD are still lacking [9]. Second, the observers had different levels of expertise. However, these different
levels reflect daily practice and, most importantly, the agreement scores were comparable.
Third, only one reader of each education level was recruited, so we did not perform
a subgroup analysis of intra- and interobserver agreement among readers with comparable
levels of experience. However, the results of our study demonstrate a high reliability,
even in the case of different education levels. Therefore, interobserver agreement
among specialists or residents should be less important.
Conclusion
The Classification of Diverticular Disease is a feasible, easy-to-use classification,
which can be readily applied in the clinical routine by radiologists with different
levels of experience. The CDD has high-grade intra- and interobserver agreement. In
particular, it allows the differentiation of acute uncomplicated and complicated diverticulitis,
which is crucial in the context of stage-adjusted therapy and prognosis.
