Acute appendicitis is a common surgical emergency, with an estimated lifetime risk of 7-8%. Delayed or inaccurate diagnosis can lead to complications such as perforation, abscess formation, and increased morbidity.^[1] While clinical evaluation remains the cornerstone for diagnosis, imaging modalities like ultrasound (USG), computed tomography (CT), and magnetic resonance imaging (MRI) have enhanced diagnostic accuracy, reducing negative appendectomy rates. ^[2]

Acute appendicitis has a lifetime incidence of about 7%. It is rare in infants less than 2 years old when the appendix is funnel-shaped. Maximum incidence is around 20 years old which coincides with peak appendiceal lymphoid tissue. ^[3] Older adults have a higher incidence of perforation and underlying appendiceal tumour. ^[4] Appendicitis is the most frequent non-obstetric emergency in pregnancy and is associated with 10% foetal mortality and 0.5% maternal mortality. The gravid uterus may prevent the omentum from walling off the appendix. ^[5]

The classical presentation consists of referred periumbilical pain (T10) which within a day or two localises to McBurney’s point in the right iliac fossa and is associated with rebound tenderness, fever, nausea, vomiting, tachycardia, raised bilirubin and inflammatory markers and other signs of peritonitis. ^[6] This progression is unhelpful in children who often present with vague and non-specific signs and symptoms. It also relies on the appendix being in the right iliac fossa, however, the appendix can be located anywhere in the abdomen and even in the thorax and groin. ^[7]

Ultrasound, being non-invasive, radiation-free, and widely available, is particularly valuable in pediatric and pregnant populations. ^[8] The characteristic ultrasound findings of acute appendicitis include an enlarged, non-compressible appendix with a diameter exceeding 6 mm, increased periappendiceal echogenicity, and associated free fluid. ^[9] However, operator dependency and limitations in obese patients or those with atypical presentations pose challenges. ^[10]

This study evaluates the diagnostic performance of ultrasound in acute appendicitis by correlating sonographic findings with surgical and histopathological outcomes in a cohort of 90 patients. The study aims to underscore the strengths and limitations of ultrasound, contributing to evidence-based diagnostic algorithms.

This prospective observational study was conducted at a tertiary care teaching hospital over six months. A total of 90 patients presenting with acute abdominal pain and clinical suspicion of appendicitis were included in the study.

Inclusion Criteria: Patients of all genders aged 10 years and above. Clinical suspicion of acute appendicitis based on symptoms (right lower quadrant pain, fever, nausea, etc.) and physical examination (e.g., McBurney’s point tenderness).

Exclusion Criteria: Patients with a prior history of appendectomy. Cases with inconclusive clinical or imaging findings where alternative diagnoses were established.

Procedure: All patients underwent a standardized ultrasound examination performed by experienced radiologists using high-frequency linear probes. Key ultrasound findings included:

• Appendix diameter > 6 mm.
• Non-compressibility of the appendix.
• Presence of periappendiceal fat stranding or free fluid.

The sonographic diagnosis was categorized as positive, negative, or equivocal for appendicitis. All patients subsequently underwent surgical evaluation, and appendectomy specimens were subjected to histopathological examination, which served as the gold standard for diagnosis.

Data Analysis: Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ultrasound were calculated by comparing findings with histopathological results. Statistical analyses were performed using appropriate software.

Out of the 90 patients included in the study, 65 cases were confirmed as acute appendicitis based on histopathological examination. The key findings are summarized in the following tables.

Table 1: Diagnostic Performance of Ultrasound

In table 1, Sensitivity (84.6%): Ultrasound correctly identified 84.6% of patients with acute appendicitis, indicating its ability to detect true positive cases effectively. Specificity (78.3%): Ultrasound correctly ruled out acute appendicitis in 78.3% of patients without the condition, though some false positives were noted. PPV (91.3%): High predictive value of a positive ultrasound suggests reliable confirmation of appendicitis when ultrasound findings are positive. NPV (66.7%): The lower negative predictive value emphasizes the risk of missed diagnoses in cases of negative ultrasound, particularly in atypical presentations.

Table 2: Patient Demographics

In table 2, the study had a nearly balanced gender distribution, with a slightly higher prevalence among males (55.6%). The mean age of 28.6 years reflects that acute appendicitis predominantly affects young adults.

Table 3: Clinical Symptoms and Signs

In table 3, the most common symptom was right lower quadrant pain (94.4%), underscoring its diagnostic importance. Nausea/vomiting and fever were also significant but less frequent, aligning with common clinical presentations.

Table 4: Sonographic Findings

In table 4, an enlarged appendix (>6 mm) was the most frequent finding (64.4%), followed by non-compressibility (58.9%). Periappendiceal fat stranding and free fluid were less common but still significant markers of inflammation.

Table 5: Comparison of Ultrasound and Histopathology

In table 5, Ultrasound demonstrated strong correlation with histopathological results, with 59 true positives and only 6 false positives. However, 13 cases were false negatives, indicating limitations in detecting certain presentations of appendicitis.

Table 6: Negative Appendectomy Rates

In table 6, the low negative appendectomy rate (6.7%) reflects improved surgical decision-making when guided by ultrasound findings, minimizing unnecessary surgeries.

The findings of this study reinforce the diagnostic utility of ultrasound in acute appendicitis, demonstrating an overall sensitivity of 84.6% and specificity of 78.3%. These values are consistent with previous studies, highlighting ultrasound as a reliable, non-invasive imaging modality for this common surgical emergency. ^[12]

The diagnostic performance of ultrasound was particularly robust in cases with typical clinical presentations. The positive predictive value of 91.3% underscores its utility in confirming the diagnosis when findings are suggestive of appendicitis. However, the relatively lower negative predictive value (66.7%) indicates that a negative ultrasound does not definitively exclude the diagnosis, especially in patients with persistent symptoms. ^[13]

The false-negative cases in this study primarily involved patients with atypical presentations or those with a retrocecal appendix, underscoring the limitations of ultrasound in specific anatomical or clinical scenarios. ^[14] False positives were less frequent but occurred in cases of other inflammatory conditions mimicking appendicitis, such as mesenteric lymphadenitis. ^[15]

Operator dependency remains a notable limitation of ultrasound, with diagnostic accuracy heavily influenced by the experience of the radiologist. Training and standardization of ultrasound protocols are essential to minimize interobserver variability and enhance diagnostic consistency. ^[16]

Comparison with histopathological results, the gold standard, revealed that while ultrasound has limitations, its advantages of being readily available, cost-effective, and free from radiation make it an ideal first-line modality, especially in resource-limited settings. ^[17] In equivocal cases, the addition of CT or MRI can improve diagnostic accuracy, particularly in obese patients or those with atypical clinical features. ^[18]

The integration of ultrasound findings with clinical and laboratory data, such as leukocytosis or elevated C-reactive protein, further enhances diagnostic precision. Combining these modalities into a scoring system could reduce the reliance on advanced imaging and unnecessary surgical interventions. ^[19]

Overall, ultrasound’s role in improving patient outcomes is significant. Its use in reducing negative appendectomy rates, as evidenced by the low rate (6.7%) in this study, contributes to better resource utilization and minimizes patient morbidity.

Ultrasound is an effective first-line imaging modality in diagnosing acute appendicitis, offering high sensitivity and specificity. Its non-invasive nature and lack of radiation make it particularly suitable for vulnerable populations such as children and pregnant women. While limitations exist, the integration of ultrasound with clinical and laboratory findings can significantly improve diagnostic efficiency, reducing negative appendectomy rates and associated complications. Further studies with larger sample sizes and advanced imaging techniques are recommended to refine diagnostic algorithms.

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