During the study period, 244 patients were diagnosed with PID. Of these, 72 patients received a final diagnosis of TOA; 40 were treated with intravenous antibiotics (conservative treatment group), and 32 did not respond to medical treatment and needed further surgery or abscess drainage (surgical interventional group). Table 1 shows the patient demographic data for the two groups. The overall median age was 31.1 years (interquartile range: 25.2–42.5 years) in the conservative treatment group and 47 years (interquartile range: 41.8–50 years) in the surgical intervention group; the difference was significant (p < 0.001). There were no significant between-group differences in BMI, number and type of previous abdominal surgeries, IUD use, history of previous PID, alcohol, or smoking. The numbers of patients who were nulliparous (p < 0.001), single (p < 0.001), and premenopausal (p = 0.003) were significantly higher in the conservative treatment group.
Table 2 shows clinical and laboratory data from the records of the two groups of patients with TOA. There were no significant differences in peak fever, fever higher than 38℃, mass location, imaging modality, and tumor maker (CA 125) level. The median (interquartile range) WBC count, ESR, CRP, mass size, and length of hospital stay were higher in the surgical intervention group than in the conservative treatment group: 9,775.0 µl (7842.5–12547.5) vs 12,600 µl (10460–15.57), p = 0.006; 34 mm/h (22.5–60.3) vs 56.5 mm/h (49.7–86.0), p < 0.001; 42.7 mg/l (13.2–106.4) vs 119.0 mg/l (69.8–190), p = 0.001; 5.1 cm (4.4–5.7) vs 6.9 cm (6.0–7.6), p < 0.001; and 6.0 days (5.0–9.0) vs 7.0 days (4.8–10.4), p = 0.017, respectively.
Table 3 shows the surgery and pathology outcomes in the 32 patients comprising the surgical intervention group. Laparoscopy and laparotomy were performed in 17 (53.1%) and 14 (43.8%) patients, respectively. One patient was treated with abscess drainage via culdotomy and pigtail insertion, 15 patients underwent unilateral salpingectomy or unilateral salpingo-oophorectomy, and 12 patients underwent bilateral salpingectomy or bilateral salpingo-oophorectomy. Four cases of total hysterectomy in addition to adnexal surgery were identified. Four patients underwent appendectomy because the TOA spread to the periappendiceal area. One patient underwent low anterior resection because the TOA resulted from colon cancer with perforation. Fistulectomy was performed in one patient with a fistula between the TOA and abdominal skin. Two patients were diagnosed with actinomycosis.
Univariate analysis was performed by binary logistic regression. Multivariate analysis was performed and cutoff values based on the ROC curve were determined using variables found to be significant in the univariate analysis. As shown in Table 4, five variables remained significantly associated with the risk of surgical intervention: age (OR, 1.134; 95% confidence interval [CI], 1.065–1.209); mass size (OR, 1.947; 95% CI, 1.313–2.887); ESR (OR, 1.037; 95% CI, 1.016–1.059); CRP (OR, 1.012; 95% CI, 1.004–1.019); and WBC (OR, 1.000; 95% CI, 1.000–1.000). Only age (p = 0.001) and ESR (p = 0.045) remained significant variables in the multivariate analysis. Mass size showed borderline significance (p = 0.065).
Table 5 shows cutoff values and AUC based on the ROC curve for variables found to be significant in the univariate analysis. Sensitivity, specificity, accuracy, PPV, and NPV were calculated using the cutoff values. As a single variable, age (cutoff value > 34.3 years and AUC 0.822) showed the highest sensitivity (93.8%) and NPV (87.5%) for predicting surgical intervention in TOA patients. However, the specificity of age was only 35%. The accuracy of mass size (cutoff value > 5.9 cm, AUC 0.780) was the highest and ESR (cutoff value 45 mm/h and AUC 0.750) showed the highest PPVs (Fig. 1).
To increase the predictability, age and ESR, which were significant variables in the multivariate analysis, were combined. The combination index of age > 34.2 years and ESR > 45 mm/h had an accuracy of 81.9%, which was higher than that of the single variables. Risk scoring was performed based on age, ESR, and mass size. Each variable with a value higher than the cutoff value received a scored of 1, and the combination of variables resulting in a total score of more than 2 points was categorized as the risk group. The AUCs of the risk group and combination index were 0.844 (sensitivity 93.8%, specificity 75.0%, accuracy 83.3%, PPV 75%, and NPV 93.8%) and 0.819 (sensitivity 81.3%, specificity 82.5%, accuracy 81.9%, PPV 78.8%, and NPV 84.6%), respectively (Fig. 2).