Added value of ratio of cross diameters of the appendix in ultrasound diagnosis of acute appendicitis

Table 1 The baseline characteristics of the patients with a normal appendix and acute appendicitis and sonographic characteristics

Item	Normal appendix (n = 112)	Acute appendicitis (n = 233)	Statistics (t/χ2/Z)	P value
Sex, n (%)			14.2882	< 0.001
Male	29 (25.9)	110 (47.2)
Female	83 (74.1)	123 (52.8)
Age (yr) M (IQR)	31.0 (24.0, 39.8)	37.0 (28.0, 49.5)	-3.4093	0.001
Detectable length (mm) M (IQR)	34.8 (29.8, 43.9)	53.2 (45.0, 64.7)	-10.1643	< 0.001
SD (mm, mean ± SD)	4.9 ± 0.9	9.9 ± 2.0	-31.7221	< 0.001
LD (mm, mean ± SD)	6.5 ± 1.0	10.7 ± 2.2	-24.3401	< 0.001
RATIO (mean ± SD)	1.32 ± 0.16	1.09 ± 0.07	15.0711	< 0.001
Mural lamina n (%)			49.9492	< 0.001
Clear	110 (98.2)	146 (62.7)
Ambiguous	2 (1.8)	87 (37.3)
Mural vascularity, n (%)			32.6942	< 0.001
Present	12 (10.7)	96 (41.2)
Absent	100 (89.3)	137 (58.8)
Luminal echogenicity, n (%)
Thread-like high echoic	62 (55.4)	0 (0)
Anechoic	2 (1.8)	63 (27.0)
Hypoechoic	36 (32.1)	58 (24.9)	197.3082	< 0.001
Isoechoic	9 (8.0)	13 (5.6)
Hyperechoic, shadowing	1 (0.9)	33 (14.2)
Complex echoic	2 (1.8)	66 (28.3)
MOD (mm), n (%)
> 6	77 (68.8)	231 (99.1)	72.9712	< 0.001
≤ 6	35 (31.2)	2 (0.9)
> 7	30 (26.8)	229 (98.3)	206.6222	< 0.001
≤ 7	82 (73.2)	4 (1.7)
> 8	10 (8.9)	212 (91.0)	222.0152	< 0.001
≤ 8	102 (91.1)	21 (9.0)

¹t value.

²χ² value.

³Z value.

M: Median; IQR: Interquartile range; SD: Short diameter on the cross-section; LD: Long diameter on a cross-section; RATIO: LD/SD; MOD: Maximum outer diameter.

Table 2 Diagnostic performances of different criteria for evaluating acute appendicitis

Item	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	AUC (95%CI)
RATIO (1.18)	91.0	83.0	91.8	81.6	0.870 (0.830-0.904)
MOD (> 6 mm)	99.1	31.3	75.0	94.6	0.652 (0.599-0.702)
RATIO + MOD > 6 mm	90.1	92.0	95.9	81.7	0.910 (0.875-0.938)

RATIO: Ratio of the cross diameters of the appendix; MOD: Maximum outer diameter on the transverse section of the appendix; PPV: Positive predictive value; NPV: Negative predictive value; AUC: Area under the receiver operating characteristic curve.