An interpretable and transparent machine learning framework for appendicitis detection in pediatric patients.

Appendicitis, an infection and inflammation of the appendix is a prevalent condition in children that requires immediate treatment. Rupture of the appendix may lead to several complications, such as peritonitis and sepsis. Appendicitis is medically diagnosed using urine, blood, and imaging tests. In recent times, Artificial Intelligence and machine learning have been a boon for medicine. Hence, several supervised learning techniques have been utilized in this research to diagnose appendicitis in pediatric patients. Six heterogeneous searching techniques have been used to perform hyperparameter tuning and optimize predictions. These are Bayesian Optimization, Hybrid Bat Algorithm, Hybrid Self-adaptive Bat Algorithm, Firefly Algorithm, Grid Search, and Randomized Search. Further, nine classification metrics were utilized in this study. The Hybrid Bat Algorithm technique performed the best among the above algorithms, with an accuracy of 94% for the customized APPSTACK model. Five explainable artificial intelligence techniques have been tested to interpret the results made by the classifiers. According to the explainers, length of stay, means vermiform appendix detected on ultrasonography, white blood cells, and appendix diameter were the most crucial markers in detecting appendicitis. The proposed system can be used in hospitals for an early/quick diagnosis and to validate the results obtained by other diagnostic modalities.

Chronic appendicitis misdiagnosed as a periappendiceal orifice polyp: a case report.

BACKGROUND: Unlike acute appendicitis, chronic appendicitis is characterized by nonspecific abdominal pain and intermittent course. This may lead to late diagnosis or misdiagnosis, with the possibility of serious complications. CASE REPORT: A male patient of Arab origin aged 55 years had a 2-year history of recurrent episodes of mild pain in the right lower quadrant of the abdomen. The episodes were associated with nausea, chills, and abdominal bloating but no vomiting, rectal bleeding, or weight loss. On examination, the patient showed soft and lax abdomen with mild tenderness in the right lower quadrant, with no organomegaly or abdominal masses. Laboratory findings showed normal complete blood count and C-reactive protein. The patient underwent colonoscopy to rule out malignancy, which showed appendiceal orifice polyp that required resection. The computed tomography scan showed an enlarged appendix with multiple intraluminal dense appendicoliths. The largest stone at the appendiceal orifice measured 1.5 cm × 0.9 cm and was partially protruding within the cecal lumen. The diagnosis of chronic appendicitis was confirmed. The patient underwent appendectomy and was asymptomatic a few days after discharge. CONCLUSIONS: We are reporting a patient with chronic appendicitis presented with multiple appendicoliths. The patient was initially misdiagnosed as periappendiceal orifice polyp. The current finding highlights the importance of imaging, especially computed tomography in confirming the diagnosis in patients with atypical appendicitis presentation.

Comparative study of imaging features in uncomplicated and complicated acute appendicitis.

BACKGROUND: Acute appendicitis is a common cause of acute abdominal pain necessitating surgical intervention. While the traditional treatment has been urgent appendectomy, recent studies suggest that an antibiotics-first approach can be safe for uncomplicated cases. Classifying appendicitis into uncomplicated and complicated categories is crucial for guiding treatment decisions and predicting patient outcomes. This study aims to evaluate the distinct imaging findings associated with uncomplicated appendicitis and its complicated subtypes-phlegmonous, gangrenous, and perforated appendicitis-to aid in differential diagnosis. METHODS: This retrospective observational study was conducted from January 2014 to December 2023 and included 1,250 patients (492 women, 758 men) who underwent an appendectomy with available pathology results. After excluding 56 patients with normal pathology, 52 with non-appendicitis pathologies, and 48 with inaccessible computed tomography (CT) images, 1,094 patients were analyzed. CT images were evaluated for appendiceal diameter, wall thickness, cecal wall thickness, periappendiceal fat stranding, effusion, lymphadenopathy, intraluminal and free periappendiceal air, mucosal hyperenhancement, and the presence of appendicolith. RESULTS: The diameter of the appendix, along with the presence of periappendiceal air, effusion, and intraluminal appendicolith, were significantly higher in the perforated appendicitis group compared to other groups (p<0.05). Periappendiceal fat stranding, evaluated as a binary variable, did not show significant differences among the groups. Appendiceal wall thickness was higher in the perforated group and lower in the non-perforated gangrenous group compared to the uncomplicated group (p<0.05). No significant correlation was found for mucosal hyperenhancement between the appendicitis subgroups. Intraluminal air, though normal in a healthy appendix, was a specific predictor of complicated appendicitis when combined with other findings. CONCLUSION: This study provides a detailed analysis of distinct imaging findings associated with uncomplicated and complicated appendicitis. Key differentiators such as appendiceal diameter, periappendiceal air, effusion, and intraluminal appendicolith are crucial for accurate diagnosis. The findings highlight the importance of these parameters in distinguishing various types of appendicitis, offering valuable insights for clinical practice. Future prospective studies and advanced imaging techniques are needed to validate these findings and enhance the diagnosis and management of acute appendicitis and its complications.

Predictive model for identification of gangrenous or perforated appendicitis in adults: a multicenter retrospective study.

BACKGROUND: Gangrene and perforation are severe complications of acute appendicitis, associated with a higher mortality rate compared to uncomplicated appendicitis. Accurate preoperative identification of Gangrenous or perforated appendicitis (GPA) is crucial for timely surgical intervention. METHODS: This retrospective multicenter study includes 796 patients who underwent appendectomy. Univariate and multivariate logistic regression analyses are used to develop a nomogram model for predicting GPA based on laboratory tests and computed tomography (CT) findings. The model is validated using an external dataset. RESULTS: Seven independent predictors were included in the nomogram: white blood cell count, lymphocyte count, D-dimer, serum glucose, albumin, maximum outer diameter of the appendix, and presence of appendiceal fecalith. The nomogram achieved good discrimination and calibration in both the training and testing sets. In the training set, the AUC was 0.806 (95%CI: 0.763-0.849), and the sensitivity and specificity were 82.1% and 66.9%, respectively. The Hosmer-Lemeshow test showed good calibration (P = 0.7378). In the testing set, the AUC was 0.799 (95%CI: 0.741-0.856), and the sensitivity and specificity were 70.5% and 75.3%, respectively. Decision curve analysis (DCA) confirmed the clinical utility of the nomogram. CONCLUSION: The laboratory test-CT nomogram model can effectively identify GPA patients, aiding in surgical decision-making and improving patient outcomes.

Impact of an appendicolith and its characteristics on the severity of acute appendicitis.

BACKGROUND: Antibiotics have been reported as an efficient and safe treatment option for uncomplicated acute appendicitis without an appendicolith diagnosed using computed tomography (CT). The aim of this study was to assess the association of a CT-diagnosed appendicolith and its characteristics with appendicitis severity. METHODS: A large prospective patient cohort with suspected acute appendicitis enrolled between April 2017 and November 2018 was retrospectively reviewed. The initial analysis evaluated the association of a CT-diagnosed appendicolith with complicated acute appendicitis; then, based on the availability of CT images, a subset of patients was analysed for the correlation of appendicolith characteristics with appendicitis severity. The final appendicitis assessment (uncomplicated or complicated-including perforation, gangrene, an abscess, or a tumour) was determined for all patients. RESULTS: Out of 3512 eligible patients, 3085 patients with appendicitis were selected and 380 patients with an appendicolith and with a CT image available for reassessment were included. Out of the 3085 patients with CT-diagnosed acute appendicitis, 1101 (35.7%) patients presented with both acute appendicitis and an appendicolith and, out of these, 519 (47.1%) had complicated acute appendicitis. In the patients without an appendicolith (1984 patients), 426 (21.5%) had complicated appendicitis (P < 0.001). Re-evaluation of CT images for 380 patients showed that a larger appendicolith diameter (OR = 1.15 (95% c.i. 1.06 to 1.25); P < 0.001), appendicolith location at the base of the appendix (55.1% versus 44.9%; P = 0.008), and heterogeneous appendiceal wall enhancement around the appendicolith (68.4% versus 31.6%; P < 0.001) were associated with an increased risk of complicated acute appendicitis. CONCLUSION: The presence of an appendicolith in patients with acute appendicitis is correlated with the risk of complicated appendicitis. This risk is further increased by a larger appendicolith diameter or appendicolith location at the base of the appendix.

Colonoscopy diagnosis of recurrent abdominal pain in a 4-year-old boy with intestinal duplication cyst involving colon, appendix, and ileum: a case report.

BACKGROUND: Intestinal duplication cyst is an infrequent congenital malformation that can involve all the segments of the gastrointestinal tract. The cases of intestinal duplication cyst involving the colon, appendix, and ileum in children are particularly uncommon. The symptoms of abdominal pain are similar to other acute abdominal diseases in children, such as appendicitis, intussusception, and intestinal obstruction, so sometimes its diagnosis is challenging and leads to misdiagnosis. CASE PRESENTATION: We report a 4-year-old Asian boy who presented to the pediatric emergency department with abdominal pain and vomiting but no fever, peritonitis, or mass. No abdominal abnormality was found via radiology and ultrasonography. After 2 days' anti-inflammatory therapy, the patient was discharged with pain relief. A total of 9 months later, he was readmitted to the pediatric emergency department for the same complaint as the first admission. Abdominal physical examination and ultrasound examination were still negative. Barium examination found a large mass in the colon. Colonoscopy was performed before operation to confirm the rare co-cavity intestinal duplication cyst involving the colon, appendix, and ileum. After resection of intestinal duplication and ileocolonic anastomosis, the patient's abdominal pain and vomiting has not recurred for 5 years postoperatively. CONCLUSIONS: The diagnosis of intestinal duplication cyst in children is difficult, especially the rare co-cavity and long segmental intestinal duplication, which is easily misdiagnosed. Colonoscopy may be an effective auxiliary diagnostic method, especially for diseases that are difficult to diagnosed clinically, such as recurrent abdominal pain.

An FUO patient diagnosed as appendicitis: a case report.

BACKGROUND: The diagnosis and management of fever of unknown origin pose significant challenges in the field of infectious diseases, as it is influenced by various factors. Infectious diseases have long been recognized as the primary etiology of fever of unknown origin. However, not all infectious diseases can definitively identify the causative pathogen and infection sites. CASE PRESENTATION: we present a case report of an individual with fever, nausea, and anorexia but did not report any abdominal pain. Physical examination revealed no signs of abdominal tenderness. Repeated imaging studies including enhanced CT and color US of the appendix, only one color US suggested the possibility of appendicitis. Despite effective anti-infective treatment, the patient continued to experience low-grade fever, leading to the decision for laparoscopic exploration and subsequent appendectomy. Pathological findings confirmed the presence of appendicitis. After the surgical procedure, the patient's temperature and infectious markers returned to within normal range, ultimately leading to a diagnosis of appendicitis. CONCLUSIONS: The atypical symptoms and signs, along with the negative imaging results, contribute to the under diagnosis of appendicitis and the progression of fever of unknown origin, thereby exacerbating the physical, mental, and economic burden on patients. Consequently, there are valuable insights to be gained regarding the management of both appendicitis and fever of unknown origin.

Is appendoscope a new option for the treatment of acute appendicitis?

Acute appendicitis is a common surgical emergency. It is commonly caused by obstruction of the appendiceal lumen due to fecaliths, tumors, or lymphoid hyperplasia. For over a century, appendectomy has been the primary treatment for acute appendicitis. Abraham Groves performed the first open appendectomy in 1883. In 1983, Kurt Semm completed the first laparoscopic appendectomy, heralding a new era in appendectomy. However, appendectomy is associated with certain complications and a rate of negative appendectomies. Studies have suggested controversy over the impact of appendectomy on the development of inflammatory bowel disease and Parkinson's disease, but an increasing number of studies indicate a possible positive correlation between appendectomy and colorectal cancer, gallstones, and cardiovascular disease. With the recognition that the appendix is not a vestigial organ and the advancement of endoscopic te-chnology, Liu proposed the endoscopic retrograde appendicitis therapy. It is an effective minimally invasive alternative for treating uncomplicated acute appendicitis. Our team has developed an appendoscope with a disposable digital imaging system operated through the biopsy channel of a colonoscope and successfully applied it in the treatment of appendicitis. This article provides an overview of the progress in endoscopic treatment for acute appendicitis and offers a new perspective on the future direction of appendiceal disease treatment.

Appendicolith classification: physical and chemical properties of appendicoliths in patients with CT diagnosed acute appendicitis - a prospective cohort study.

OBJECTIVE: Appendicoliths are associated with a more complicated course of acute appendicitis and failure of non-operative treatment. We aimed to update the appendicolith classification originally described in 1966 and to assess the association of appendicolith characteristics with appendicitis severity. DESIGN: This prospective predefined MAPPAC-trial (ClinicalTrials.gov NCT03257423) substudy included patients with CT diagnosed appendicitis presenting with an appendicolith. CT visible appendicoliths were harvested at surgery, measured and characterised by morphological examination complemented with micro-CT and micro-X-ray fluorescence spectroscopy. Patients were categorised into two groups: appendicolith appendicitis without other complications and appendicolith appendicitis with complications (appendiceal gangrene, perforation and/or abscess). The association of appendicolith classification and characteristics with appendicitis severity was evaluated. RESULTS: Of 78 patients with a CT appendicolith, 41 appendicoliths were collected and classified based on the degree of hardness into three classes. The hardest appendicoliths (class 3) were less common (19.5%) presenting with a stone-hard outer layer and concentrically layered inner structure around a core. The layered inner structure was also observed in class 2 appendicoliths, but was absent in soft, class 1 appendicoliths. Appendicolith hardness or measures (maximum length, diameter and weight) were not associated with appendicitis severity. The spatial distribution of the main inorganic elements of calcium and phosphorus varied within most appendicoliths. CONCLUSION: This updated classification confirms categorisation of CT visible appendicoliths into three classes based on their physical and chemical characteristics. The data on clinical and aetiopathological characteristics of appendicoliths is scarce and using this systematic classification would add to this understanding.

Mucocoele of the appendix.

Introduction: Mucocoele of the appendix occurs in 0.2-0.7% of people in the world without any well-defined clinical symptoms. It occurs when there is an accumulation of mucous in the lumen of the appendix. Case Presentation: We present three cases: a 48-year-old male admitted to the emergency room with a one-day history of right iliac fossa pain. Abdominal examination was suggestive of acute appendicitis. The initial abdominal computerised tomography scan was reported as being unremarkable. At surgery, a firm tumour of the appendix was found, and a limited right hemicolectomy was done. Histopathology confirmed a mucocoele of the appendix with borderline mucinous histology.The second case is a 63-year-old man who presented with a one-year history of abdominal distension and weight loss. Previous abdominal ultrasound was suggestive of liver cirrhosis with significant ascitic fluid. Abdominal magnetic resonance imaging found an appendix mucocoele with infiltration of the omentum and scalloping of the liver surface suggestive of pseudomyxoma peritonei. A percutaneous biopsy of the omental mass confirmed metastatic mucinous adenocarcinoma of the appendix.The third case is a 68-year-old man who, during an annual medical check-up, had an incidental finding of a cystic right iliac fossa mass on ultrasound, confirmed on abdominopelvic computerised tomography scan to be an appendix mucocele. He had laparoscopic appendicectomy. The histopathological diagnosis confirmed a mucinous cystadenoma of the appendix. Conclusion: Preoperative diagnosis of appendiceal mucocoele is difficult and commonly discovered intraoperatively. The prognosis is good for the histologically benign type, but it is poor when malignant or peritoneal lesions are present. Funding: None declared.

Schistosomal appendicitis: a case report.

BACKGROUND: Schistosomiasis is one of the endemic parasitic diseases in many developing countries. Despite this, appendicitis secondary to schistosomiasis is an uncommon condition even in some endemic areas. Schistosomal appendicitis, an incidentally discovered appendicitis associated with schistosomiasis histological findings, affects young males predominantly. Timely diagnosis and treatment, including appendectomy and anti-helminthic therapy, are crucial. CASE REPORT: A 24-year-old Sudanese male patient presented with abdominal pain. Diagnosed with acute appendicitis, he underwent appendectomy, revealing appendix inflammation with Schistosoma ova in histopathology. Abdominal ultrasound detected no complications. Weakly positive Schistosoma serology was noted, but stool and urine analysis showed no infection evidence. Prescribed praziquantel, patient had 3-year post-op follow-up without complications. CONCLUSIONS: This case report underscores the significance of including schistosomiasis in the differential diagnosis of appendicitis, particularly in regions where the disease is endemic. It underscores the necessity of histopathological evaluations for accurate diagnosis, emphasizing the potential implications for clinical practice in similar settings.

Introducing the ratio of cross diameters of the appendix for ultrasound diagnosis of acute appendicitis can significantly increase specificity.

PURPOSE: To validate whether the introduction of the ratio of the cross diameters on the transverse section of the appendix (RATIO) ≤ 1.18 is useful for improving the ultrasound diagnosis of acute appendicitis (AA). METHODS: Data from 220 patients with AA and 110 patients with a normal appendix were retrospectively studied. The RATIO ≤ 1.18, maximal outer diameter (MOD) > 6 mm, and a combination of RATIO ≤ 1.18 and MOD > 6 mm were used for predicting AA. The area under the receiver operating characteristic curve (AUC), sensitivity, specificity, positive and negative predictive values (PPV and NPV) were calculated. RESULTS: The RATIO ≤ 1.18, MOD > 6 mm, and a combination of RATIO ≤ 1.18 and MOD > 6 mm for predicting AA showed a sensitivity of 90, 100, and 90%; specificity of 79.1, 27.3, and 88.2%; and AUC of 0.845, 0.636, and 0.891, respectively. When comparing the outcomes between MOD > 6 mm and a combination of MOD > 6 mm and RATIO ≤ 1.18, the specificity and PPV increased from 27.3 to 88.2% and 73.3 to 93.8%, respectively (all P < 0.0001). The sensitivity and NPV decreased from 100 to 90% and 100 to 81.5%, respectively (all P < 0.0001). The AUC increased from 0.636 to 0.891 (P < 0.0001). When comparing the AUC of MOD > 6 mm, and a combination of RATIO ≤ 1.18 and MOD > 6 mm for predicting AA with the AUC in a previous study, there were no significant differences between each other (all P > 0.05). CONCLUSION: Introducing the RATIO ≤ 1.18 for the evaluation of AA can improve the diagnostic performance and significantly increase specificity.

Immunoglobulin G4-related disease mimicking an appendiceal neoplasm: a case report.

Immunoglobulin G4-related disease (IgG4-RD) is a fibroinflammatory condition characterized by chronic activation of the immune system and a tendency to form tumorous lesions. IgG4-RD is frequently characterized by the presence of tumor-like masses affecting multiple organs and is easily mistaken for a malignant neoplasm. However, IgG4-RD affecting the appendix is extremely rare, with only seven cases reported previously. We report the case of a woman in her early 60s who presented with insidious abdominal pain and radiological findings mimicking appendiceal neoplasms. After diagnosing appendiceal neoplasms, surgery was performed. The patient had a serum IgG4 concentration of <1.35 g/L, which did not satisfy one of the three revised comprehensive diagnostic criteria for IgG4-RD. A pathological examination was conducted, and the patient was diagnosed with appendiceal IgG4-RD. To the best of our knowledge, there have been no previously reported cases of IgG4-RD affecting the appendix in patients with low serum IgG4 concentrations. This report may prove beneficial for the future understanding of IgG4-RD and for the revision of diagnostic and treatment strategies.

Partial visualization of appendix on ultrasound: What does it mean in the child with suspected appendicitis?

BACKGROUND: Visualization of the entire appendix, including the tip, is thought, but has not been demonstrated, to be important for exclusion of appendicitis by ultrasound. OBJECTIVE: To determine if incomplete visualization of the appendix has negative clinical ramifications including missed appendicitis. METHODS: Under IRB approval we retrospectively reviewed right lower quadrant ultrasound reports from January 2017 to December 2020 to identify examinations with impressions of full visualization of the normal appendix, non-visualization of the appendix with and without secondary findings of appendicitis, and partial visualization of the appendix. Electronic health records were reviewed for follow-up imaging within 48 h, and surgery with pathology reports (if available). RESULTS: 12,193 examinations were included. 4171 (34.2 %) had full visualization of a normal appendix, 5369 (44.0 %) had non-visualization with no secondary findings, and 234 (1.9 %) had non-visualization with secondary findings, The frequencies of appendicitis in these three groups were 34 (0.8 %), 283 (5.3 %), and 127 (54.3 %) respectively. The appendix was partially visualized in 338 (2.8 %) patients with secondary findings present in 53 (15.6 %). Partial visualization without secondary findings had a similar frequency (4.9 %, 14/285) of appendicitis to non-visualized appendix without secondary findings (p = 0.797) and a higher frequency than full visualization of a normal appendix (p < 0.0001). Partial visualization with secondary findings had similar rates (54.7 %, 29/53) to non-visualized appendix with secondary findings (p = 0.953). CONCLUSION: Partial visualization of the appendix with ultrasound (with and without secondary findings) is associated with similar frequencies of appendicitis as non-visualization of appendix (with and without secondary findings).

Predictive factors for recurrent acute appendicitis after conservative treatment.

INTRODUCTION: Conservative treatment of acute appendicitis is gaining popularity, and identifying patients with a higher risk of recurrence is becoming increasingly important. Previous studies have suggested that older age, male sex, diabetes, appendicolith and abscess formation may be contributing factors, however, results from the adult population are inconsistent. AIM: This study aims to identify predictive factors for recurrent appendicitis after conservative treatment. METHODS: This retrospective study included patients with conservatively treated acute appendicitis at Skåne University Hospital, Sweden during 2012-2019. Information on patient demographics at index admission and follow-up data were retrieved from medical charts and radiologic images. Uni -and multivariable logistic regression analysis were performed using Stata Statistical Software. RESULTS: In total, 379 patients with conservatively treated acute appendicitis were identified, of which 78 (20.6%) had recurrence. All patients were followed-up for a minimum of 41 months after the first diagnosis of acute appendicitis unless appendectomy after successful conservative treatment or death occurred during follow-up. The median time to recurrence was 6.5 (1-17.8) months. After multivariable logistic regression analysis, external appendix diameter >10 mm [OR 2.4 (CI 1.37-4.21), p = .002] and intra-abdominal abscess [OR 2.05 (CI 1.18-3.56), p = .011] on computed tomography were significant independent risk factors for recurrent appendicitis. Appendicolith was not associated with an increased risk of recurrence. CONCLUSION: This study suggests abscess formation and appendix distension of >10 mm to be potential risk factors for recurrent acute appendicitis after initial successful conservative treatment.

Predictive values of indirect ultrasound signs for low risk of acute appendicitis in paediatric patients without visualisation of the appendix on ultrasound.

BACKGROUND AND OBJECTIVES: The ability to rule appendicitis in or out using ultrasound is limited by studies where the appendix is not visualised. We determined whether the absence of indirect ultrasound signs can rule out appendicitis in children undergoing a radiology-performed ultrasound in which the appendix is not visualised METHODS: This was a single-centre retrospective observational study of patients aged 3-13 with a clinical suspicion of acute appendicitis evaluated in a Paediatric Emergency Department in Spain from 1 January 2013 to 31 December 2019. For those patients who had formal ultrasound, direct and indirect findings of ultrasound were abstracted from the ultrasound report. The surgical pathology report was established as the gold standard in patients who underwent an appendectomy. In those who did not, appendicitis was considered not to be present if there was no evidence in their charts that they had undergone an appendectomy or conservative therapy for appendicitis during the episode. The main outcome variable was the diagnosis of acute appendicitis. For patients undergoing ultrasound, the independent association of each indirect ultrasound sign with the diagnosis of appendicitis in patients without a visualised appendix was analysed using logistic regression. RESULTS: We included 1756 encounters from 1609 different episodes. Median age at the first visit of each episode was 10.1 years (IQR, 7.7-11.9) and 921 (57.2%) patients were men. There were 730 (41.6%) encounters with an Alvarado score ≤3, 695 (39.6%) with a score 4-6 and 331 (18.9%) with a score ≥7. Appendicitis was diagnosed in 293 (17.8%) episodes. Ultrasonography was performed in 1115 (61.6%) encounters, with a visualised appendix in 592 (53.1%).The ultrasound findings independently associated with appendicitis in patients without a visualised appendix were the presence of free intra-abdominal fluid in a small quantity (OR:5.0 (95% CI 1.7 to 14.6)) or in an abundant quantity (OR:30.9 (95% CI 3.8 to 252.7)) and inflammation of the peri-appendiceal fat (OR:7.2 (95% CI 1.4 to 38.0)). The absence of free fluid and inflammation of the peri-appendiceal fat ruled out acute appendicitis in patients with an Alvarado score <7 with a sensitivity of 84.6% (95% CI 57.8 to 95.7) and a negative predictive value of 99.4% (95% CI 97.8 to 99.8). CONCLUSIONS: Patients with an Alvarado score <7 and without a visualised appendix on ultrasound but who lack free fluid and inflammation of the peri-appendiceal fat are at very low risk of acute appendicitis.