Up-to-Date Diagnostic CT Standards for Acute Appendicitis: Wall Thickness and Intraluminal Fluid Thickness

Acute appendicitis is a prevalent condition that requires accurate and timely diagnosis and management to avoid potential complications. Classically, the diagnosis of appendicitis is made using the appendicular outer-to-outer wall diameter. In this study, we examined the sensitivity and specificity of computed tomography (CT) scans for diagnosing acute appendicitis using wall thickness and lumen thickness rather than diameter. This study included data from 350 patients who presented to the emergency department with clinically suspected acute appendicitis. All patients underwent a CT scan, and 62 radiologically positive patients underwent surgery. A radiological diagnosis was made using the conventional outer-to-outer wall diameter with a cut-off of 6 mm for a positive diagnosis. These 62 positive CT scans were reviewed and compared with surgical results. The study showed that a threshold of 2.25 mm for appendicular lumen thickness is an excellent diagnostic tool for acute appendicitis, demonstrating a high sensitivity of 96.4% and a lower specificity of 67%. In contrast, 1.6 mm wall thickness indicates acute appendicitis, with 81.8% sensitivity and 84% specificity. However, the wall thickness remains inferior to the conventionally used measurement of 6.75 mm for appendicular diameter, with a sensitivity of 87.5% and a specificity of 100%.


Introduction
Appendicitis is one of the most common causes of acute abdomen in adults and has a lifetime risk of 6%-7% [1].It is defined as inflammation of the vermiform appendix, an acute condition that presents within 24 hours [2].
Multiple imaging modalities, including abdominal computed tomography (CT), ultrasonography, and magnetic resonance imaging (MRI), aid in the clinical diagnosis of appendicitis [2].Recently, CT scans with high accuracy have been widely used in acute settings [2].Moreover, CT scans provide high-resolution images that better evaluate potential complications, eliminate differential diagnoses, and limit unnecessary surgical explorations [3,4].Consequently, the number of unnecessary appendectomies has significantly decreased owing to the use of CT scans.Further, the perforation rate decreases in parallel.
The primary criteria for a CT scan to diagnose acute appendicitis are appendicular swelling, defined as an appendicular diameter greater than 6 mm, and periappendiceal inflammatory alterations.Nevertheless, normal appendices with a diameter >6 mm are frequently encountered in daily practice [5].In contrast, we occasionally encounter patients with appendicitis who do not exhibit significant periappendiceal inflammation [5].
There are no reports describing the differences observed in CT parameters between a normal appendix of more than 6 mm and an inflamed appendix that does not exhibit periappendicular fat stranding.Differentiation between these entities may be challenging, especially without a clear clinical presentation, such as in cases of vague abdominal pain.In this study, we evaluated the accuracy of measuring appendicular wall thickness and intraluminal fluid thickness as supportive methods for CT scans in diagnosing acute appendicitis.

Study design
This study is a retrospective cross-sectional study conducted at King Abdulaziz University Hospital, Jeddah, Saudi Arabia.The study analyzed data from 350 CT scans of patients who presented to the emergency department with clinically suspected acute appendicitis and correlated it with the final diagnosis by reviewing the emergency room notes and progress notes in the surgical notes.Sixty-two patients were positive for CT scan criteria and underwent surgery.The CT scans of these 62 patients were reviewed for lumen thickness and wall thickness and compared with the surgical results of the patients.

Inclusion criteria
The study included all positive CT scans for acute appendicitis that were confirmed positive after surgery.A radiological diagnosis of acute appendicitis was made using the conventional outer-to-outer wall diameter with a cut-off of 6 mm for a positive diagnosis.Patients who underwent appendectomy, percutaneous drainage, or received antibiotics were categorized as confirmed positives after confirmation from the surgeon's operation notes.

Exclusion criteria
All CT scans negative for acute appendicitis have been excluded.

Reference standard
Patients who underwent appendectomy and the surgeon's operation note documented a normal or noninflamed appendix or had alternate diagnoses and managed accordingly and did not present with similar complaints to our hospital within our research study time frame were categorized as confirmed negative.

Statistical analysis
IBM SPSS software, version 25 (IBM Corp., Armonk, NY), was used for statistical analysis.Descriptive analysis was performed using the quantitative variables' mean and standard deviation (SD).For qualitative variables, we calculated the frequencies and percentages.We calculated accuracy measures, including sensitivity, specificity, and area under the receiver operating characteristic (ROC) curve (AUC).Statistical significance was set at a confidence interval (CI) of 95% and a margin of error of < 0.05.These measurements help confidently diagnose acute appendicitis, considering that an enlarged appendix with thickened walls reflects a state of inflammation and infection.
Applying the 1.6 mm wall thickness measurement alone to diagnose acute appendicitis resulted in 81.8% sensitivity and 84% specificity.When utilizing a luminal thickness of 2.25 mm to diagnose acute appendicitis, the highest sensitivity was 96.4%, and the specificity was 67% (Table 3).[4], which are lower than those of other studies that used enhanced contrast CT.These differences may be due to variations in the study population, imaging protocols, or interpretation criteria [6].

Discussion
Appendicitis is a medical condition characterized by appendiceal inflammation.It most commonly presents as an acute condition that manifests suddenly and severely, often within 24 hours of onset [7].The classic symptoms of appendicitis include vague periumbilical pain, anorexia, nausea, vomiting, migration of pain to the right lower quadrant, and low-grade fever [8].
All patients suspected of having acute appendicitis should undergo laboratory testing, including total white blood cell count, percentage of neutrophils, and measurement of C-reactive protein concentration, before proceeding to further diagnostic steps [9].
The mean age of the participants was 34 years.The appendix had a mean length of 7 cm and a mean diameter of 8.8 mm.The mean lumen thickness of the appendix was 9.5 mm, and the mean wall thickness of the appendix was 2.3 mm.
Among the patients with surgically proven positivity, males accounted for 57.1% (32) of the positive scans, and females accounted for 42.9% (24).In addition, positive cases were less likely to have intraluminal air; however, they demonstrated appendicoliths, fat stranding, and free fluids.These features can indicate inflammation, infection, or obstruction of the appendix.In contrast, negative cases had an equal distribution between males and females, demonstrated intraluminal air, and were less likely to have any of the features above.
Appendicular diameter is commonly used in daily clinical practice for diagnosing acute appendicitis on CT.When we evaluated the accuracy of this method, we found that the 6.75 mm appendicular diameter had a sensitivity of 87.5% and a specificity of 100%.This result is compatible with prior findings in the literature, suggesting that CT is a highly accurate method for diagnosing acute appendicitis.[4].These differences may be due to variations in the study population, imaging protocols, or interpretation criteria [10].
Our proposed method suggests the application of lumen thickness and luminal thickness measurements to diagnose acute appendicitis.The results showed that 2.25 mm lumen thickness had a high sensitivity (96%) but a low specificity (67%), with an area under the ROC curve of 0.915.However, when applying 1.6 mm wall thickness, it showed a lower sensitivity of 81.8% but a higher specificity of 84%.
Overall, these results suggest that appendicular lumen thickness and wall thickness measurements on CT are important predictors of the likelihood of positive CT results in acute appendicitis.An increase in the lumen thickness was associated with a significantly higher likelihood of a positive CT result, which may aid in diagnosing acute appendicitis.
One limitation of this study is the relatively small sample size, which may limit the generalizability of the findings.Therefore, the results of this study should be interpreted with caution.Further validation studies with larger sample sizes are required to confirm our findings.

Conclusions
The study included 62 confirmed positive CT scans.The appendicular lumen thickness of 2.25 mm is an excellent diagnostic tool for acute appendicitis, demonstrating a high sensitivity of 96.4% but a lower specificity of 67%.On the other hand, 1.6 mm wall thickness has 81.8% sensitivity and 84% specificity, which is inferior to the conventional appendicular thickness, yielding a sensitivity of 87.5% and a specificity of 100%.

TABLE 1 : Descriptive analysis of the qualitative study variables
This table presents the descriptive analysis of the study variables for 62 CT examinations.