In one dog, the SLN could not be identified because of a small size. This dog was excluded from the statistical analysis, and only 27 dogs were used for the study. There were 17 different breeds represented by Rhodesian Ridgebacks (4; 14.8%), Yorkshire Terrier (3; 11.1%), Labrador Retriever (3; 11.1%), Beagle (2; 7.4%), German Shepherd (2; 7.4%), Poodle (2; 7.4%) and one (3.7%) of each (Australian Shepherd, Bohemian Shepherd, Bloodhound, Crossbreed, Czechoslovakian Wolfdog, Fox terrier, German Spitz, Hungarian Pointing Dog, Shih-Tzu, Staffordshire Bullterrier, West Highland White Terrier). There were 5 (18.5%) intact females, 4 (14.8%) spayed females, 17 (63%) intact males and one (3.7%) castrated male. The mean age of the dogs was 7.4 years (SD 3.08) with a range from 1.3 to 12.2 years. The mean weight was 23.9 kg (SD 16.11), and the range was from 2.6 to 58 kg. Nine dogs (33%) were in category ≤10 kg, eight (30%) were in the category between 10.1 to 30 kg and ten dogs (37%) were ≥30.1 kg.
The mean number of SLN was 2.1 (SD 0.6). Three dogs (11%) had only one lymph node, 17 (63%) dogs had two lymph nodes, and seven (26%) dogs had three sternal lymph nodes. The most frequent localization of the sternal lymph nodes was at the level of the second sternebra (23 dogs; 85%) (Figure 1, 2, 3). The exact SLN localization is shown in Table 1.
Table 1. Location of the sternal lymph nodes related to the adjacent sternebrae.
Position of SLN
|
Number of dogs (n=27)
|
Percentage
|
1st sternebra
|
2
|
7.4
|
1st–2nd sternebra
|
6
|
22.2
|
2nd sternebra
|
7
|
26.0
|
2nd–3rd sternebra
|
10
|
37.0
|
3rd sternebra
|
2
|
7.4
|
The longest dimension of SLN was in CrCd direction, and the shortest was in LL direction. Descriptive statistics of SLN size is shown in Table 2, and the ratio values are in Table 3.
Table 2. Descriptive statistics of the size of the lymph nodes in all three dimensions (n=27).
Statistical variable
|
CrCd (mm)
|
DV (mm)
|
LL (mm)
|
Mean ± SD
|
12.4 ± 5.02
|
5.3 ± 2.30
|
4.6 ± 1.58
|
95% CI for the mean
|
10.46 to 14.43
|
4.36 to 6.18
|
3.99 to 5.24
|
Minimum
|
2.5
|
1.3
|
1.7
|
Median
|
11.4
|
5.2
|
4.7
|
Maximum
|
21.5
|
11.2
|
7.1
|
Table 3. Table 3. Descriptive statistics of the ratio values of the lymph node size (n=27).
|
SLN to second sternebra ratio
|
SLN short-to-long axis ratio
|
Statistical variable
|
CrCd/St2DV
|
DV/St2DV
|
LL/St2DV
|
DV/CrCd
|
LL/CrCd
|
Mean ± SD
|
2.6 ± 1.44
|
0.5 ± 0.17
|
0.4 ± 0.17
|
0.45 ± 0.15
|
0.42 ± 0.20
|
95% CI for the mean
|
2.02 to 3.16
|
0.40 to 0.54
|
0.36 to 0.50
|
0.39 to 0.50
|
0.34 to 0.50
|
Minimum
|
1.3
|
0.2
|
0.2
|
0.11
|
0.16
|
Median
|
2.4
|
0.4
|
0.4
|
0.41
|
0.36
|
Maximum
|
9.1
|
1.0
|
1.0
|
0.75
|
1.24
|
SLN = sternal lymph node; St2DV = dorso-ventral dimension of the 2nd sternebra
|
There was positive correlation between the weight and the CrCd (r=0.584, p=0.0014), DV (r=0.503, p=0.0075), LL (r=0.639, p=0.0003) dimensions of SLN and also St2DV dimension (r=0.891, p<0.001). From all the ratio values, only LL/St2DV was found to correlate with the weight (r=-0.441, p=0.02). In the case of age, there was only one significant correlation with the SLN DV dimension (r=-0.528, p=0.0046). All the other parameters (SLN CrCd, SLN LL, St2DV, CrCd/St2DV, DV/St2DV, LL/St2DV, DV/CrCd, LL/CrCd) were not significantly correlated with the age (p>0.05).
The absolute size of SLN was significantly different among the weight groups. All the three dimensions were significantly different between ≤10 kg and ≥30.1 kg categories. The DV dimension was different, also between ≤10 kg and 10.1 to 30 kg (Table 4).
Table 4. Mean values of the lymph node size and ratios for different weight categories (n=27).
Parameter
|
≤10 kg (n=9)
|
10.1 to 30 kg (n=8)
|
≥30.1 kg (n=10)
|
CrCd (mm)
|
8.9*
|
13.2
|
15.0*
|
DV (mm)
|
3.5*#
|
6.1#
|
6.2*
|
LL (mm)
|
3.6*
|
4.6
|
5.5*
|
DV/CrCd
|
0.40
|
0.50
|
0.45
|
LL/CrCd
|
0.48
|
0.38
|
0.40
|
CrCd/St2DV
|
2.62
|
2.16
|
2.90
|
DV/St2DV
|
0.53
|
0.49
|
0.40
|
LL/St2DV
|
0.57*#
|
0.37*
|
0.36#
|
St2DV = dorso-ventral dimension of the 2nd sternebra. Numbers labelled with * or # are significantly different (p<0.05).
|
From the ratio values, only LL/St2DV parameter was significantly different between ≤10 kg and 10.1 to 30 kg (p=0.03) and between ≤10 kg and ≥30.1 kg (p=0.01) (Table 4). All the other ratio values were not significantly different between weight groups (p>0.05).
Except for one dog, the lymph nodes were well defined with smooth margins (26 dogs, 96.3%). In one case, the lymph node margins were assessed as not well defined. The mean precontrast and postcontrast density of the lymph node were significantly different (11.7 HU and 59.3 HU, respectively; p<0.05). The precontrast and postcontrast heterogeneity values of lymph nodes were significantly different (12.0 HU and 16.9 HU; p<0.05). The precontrast and postcontrast density of the perinodal fat was not significantly different (-104.6 HU and -102.0 HU; p=0.178). Descriptive statistics for density and heterogeneity values of SLN and density values of the perinodal fat are presented in Table 5 and 6, respectively.
Table 5.Descriptive statistics for the density values of sternal lymph nodes (n=27).
Statistical variable
|
Precontrast density (HU)
|
Postcontrast density (HU)
|
Precontrast heterogeneity (HU)
|
Postcontrast heterogeneity (HU)
|
Mean ± SD
|
11.7 ± 15.83
|
59.3 ± 29.67
|
12.0 ± 5.39
|
16.9 ± 6.39
|
95% CI for the mean
|
5.5 to 18.0
|
47.6 to 71.0
|
9.9 to 14.2
|
14.4 to 19.5
|
Minimum
|
-36.6
|
-5.8
|
4.2
|
5.4
|
Median
|
16.5
|
62.5
|
11.4
|
17.4
|
Maximum
|
39.1
|
119.7
|
27.8
|
35.9
|
Table 6. Descriptive statistics for the density values of perinodal fat (n=27).
Statistical variable
|
Precontrast density (HU)
|
Postcontrast density (HU)
|
Mean ± SD
|
-104.6 ± 19.4
|
-102.0 ± 17.9
|
95% CI for the mean
|
-112.3 to -96.9
|
-109.1 to -94.9
|
Minimum
|
-138.5
|
-132.8
|
Median
|
-104.2
|
-100.6
|
Maximum
|
-33.4
|
-39.2
|