Is pneumoperitoneum specific of post-traumatic appendicitis? Case report and literature review

Acute appendicitis and blunt abdominal trauma may co-exist, imposing a dilemma of whether there is only coincidence or there is a cause to effect relationship. The etiopathogenesis of this rare association remains obscure. Pneumoperitoneum has rarely been described in patients with acute perforative appendicitis following abdominal trauma. We report a rare case of acute perforated appendicitis after blunt abdominal trauma in an 8-year-old boy revealed by a pneumoperitoneum. We also reviewed the literature on this rare condition to assess the specificity of pneumoperitoneum in the diagnosis and to understand its etiopathogenesis. Abdominal pain and fever several days after an abdominal trauma may be a sign of post-traumatic appendicitis in the pediatric population. Pneumoperitoneum is not specific of post-traumatic appendicitis but it can be a protective sign, since it will lead to immediate laparotomy in patients with an unrecognized surgical abdomen.


Introduction
Acute appendicitis is one of the most common diagnoses in acute surgical abdominal conditions. However, isolated post-traumatic appendicitis is a rare entity and many cases remain unreported due to concurrence with other intra-abdominal injuries [1,2]. We report a rare case of an 8-year-old boy with pneumoperitoneum secondary to post-traumatic perforated appendicitis we managed at our academic institute. The report is in accordance with the SCARE guidelines 2020 [3]. We reviewed the literature on this rare condition to assess the specificity of pneumoperitoneum in the diagnosis of isolated post-traumatic acute appendicitis and to understand its etiopathogenesis.

Case report
An otherwise healthy 8-year-old boy was brought to the emergency department of our institution 10 h following a bicycle accident. He reported that he had run into a car and had struck at the lower abdomen by the bicycle's handlebar grip. He complained of abdominal pain and localized tenderness elicited by deep palpation of the right iliac fossa. The boy had no other abdominal complaints in his history before the abdominal trauma. No laceration, swelling, erythema, or tenderness was noted. No signs of trauma such as ecchymosis were detected, and the general clinical examination was normal. Blood analysis yielded hemoglobin 12.7g/dl, white blood cells (WBC) 7000/mm 3 , and C-reactive protein (CRP) 1 mg/l. Abdominal ultrasonography showed a small amount of abdominal free fluid with no sign of solid organ injury, whereas abnormal findings from the abdominal wall were not observed. Since the ultrasound was without abnormality, it was not considered essential to supplement the exploration with other radiological

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Annals of Pediatric Surgery *Correspondence: yosrakerkeni@yahoo.fr Department of Pediatric Surgery "A", Children's Hospital, Tunis El Manar University, Tunis, Tunisia examinations, and the patient was discharged home. Upon no improvement with conservative measures, the patient re-attended the emergency department 3 days later. He complained of diffuse abdominal pain with maximum in the right lower quadrant associated to anorexia, nausea, vomiting, and fever. His vital signs at admission were as follows: blood pressure 90/60 mmHg, heart rate 98/min, and respiratory rhythm 18/min. Axillary temperature was 38.7°C. Physical examination revealed generalized abdominal guarding with maximal tenderness in the right lower quadrant. The biological assessment has been redone, showing hemoglobin 12.9g/dl, WBC 13,600/mm 3 , and CRP 398 mg/l.
An erect plain abdominal X-ray was taken revealing free air under both copulae of the diaphragm (Fig. 1). Urgent abdominal ultrasonography showed a moderate free fluid on the right and left paracolic gutter and the pouch of Douglas.
In view of the evidence of free intraperitoneal gas, the history of trauma, and its mechanism, the top working diagnosis was a duodenal perforation.
A median laparotomy was performed. The stomach, duodenum, and the rest of the bowel were found to be healthy. The air leak test for perforated peptic ulcer was negative. The only pathology identified was a gangrenous appendix disinserted at its basis ( Fig. 2) leading to generalized peritonitis. There was no appendicolith, which is in favor of a traumatic disinsertion.
Appendectomy and abundant peritoneal lavage were done. Acute appendicitis with full-thickness inflammation of the appendix wall with a strong peritoneal reaction was confirmed by histopathology. The postoperative course was uneventful and the boy was discharged on postoperative day 7.

Discussion
Our patient was initially diagnosed having duodenal perforation considering the presence of pneumoperitoneum after flipping the handlebar of the bike. The diagnosis of post-traumatic appendicitis was missed.
Acute appendicitis caused by blunt abdominal trauma is very rare and has been reported sporadically in the literature [1,2]. It was more described in children [2] as the transmission of kinetic energy is more pronounced due to a smaller abdominal cavity compared with adults.
In our case, the coexistence of acute appendicitis and blunt abdominal trauma as an incidental event is very unlikely. The patient had been asymptomatic before the trauma and biological and radiological assessments were normal at the first consultation.
The rate of co-occurrence of the perforation of acute appendicitis and pneumoperitoneum is about 0 to 7% [2]. The rate of pneumoperitoneum following traumatic Fig. 1 Plain abdominal X-ray revealing free air under both copulae of the diaphragm Fig. 2 Per-operative findings. White arrow: appendicular basis. White arch: gangrenous appendix disinserted at its basis acute appendicitis has not been determined. Literature review showed that among 34 patients having post-traumatic appendicitis, almost 11% had pneumoperitoneum (Table 1) [1,.
Luminal air leak from perforated appendix resulting in pneumoperitoneum occurs when the appendiceal lumen is patent, a finding which could be more frequent in case of post-traumatic deinsertion of an initially healthy appendix. Blunt trauma might have a direct effect on the appendix with subsequent appendiceal injuries or detachment [25].
The theory which states that pneumoperitoneum might follow leakage of gas from a localized periappendiceal abscess or bacterial gas production in gangrenous appendicitis [7,8] seems also plausible since cases of post-traumatic appendicitis with pneumoperitoneum was reported in two patients having nonperforated appendicitis on surgical exploration [1,4].
An indirect mechanism with increased intra-luminal pressure or irritation caused by muscle contraction can also participate to the formation of acute appendicitis. Power contractions of the iliopsoas might irritate the appendix causing adhesions, bands, angulations, or obstructions resulting in appendicitis [26].
The review of all cases of post-traumatic appendicitis had shown that the presence of pneumoperitoneum was not a pathognomonic sign of this rare entity. The causal relationship between trauma and acute appendicitis remains unclear and the several theories suggested to explain their association remains debatable. Post-traumatic appendicitis should be considered as a differential diagnosis of hollow organ perforations in children having blunt abdominal trauma. This aims to early recognition and treatment.
Our patient fulfills all the diagnostic criteria for traumatic appendicitis [7]: There was no history of abdominal pain before trauma and the trauma was caused by a direct and violent blunt force to the abdomen of limited duration with progressive worsening of signs and symptoms.

Conclusion
Trauma is not a well-known cause of appendicitis, and this can cause a delay in early management. An interval varying from a few hours to a few days until emergence of symptoms following trauma is a very suggestive feature of post-traumatic appendicitis. Even though pneumoperitoneum is not a pathognomonic sign of post-traumatic appendicular perforation, this radiographic finding is considered to be a protective sign, since it will lead to immediate surgical exploration either by laparotomy or laparoscopy in patients with an unrecognized surgical abdomen.