Using the databases PubMed and Google Scholar, we carried out a meticulous literature search over a period between 2003 and 2023, using the key terms Amyand hernia, Amyand’s hernia and “Children” and synonyms, together with the Boolean operator AND/OR. The search resulted in 52 articles in PubMed and 548 results in Google Scholar-600 in total (Fig. 1). Eventually after the exclusion of irrelevant studies and duplications 83 pediatric case reports, 10 statistically significant case series, 8 reviews were found.

Fig. 1

PRISMA flow diagram of study selection. No legend

Definition

Rigorous terminology is needed for the correct evaluation of technical features, results, and understanding that the authors are on the same page. Found that at the beginning of the analysed period, there was a slight difference in the definition of AH in different sources. Most sources declare AH as simply the presence of an appendix [4,5,6]–herniation, harboring, or protrusion of an appendix; and few suggest mandatory incarceration of the appendix [7]. The presence of the caecum with the appendix in the hernial sac is also called Amyand sliding hernia by some [8], but most authors do not distinguish this symptom from other cases of AH. Moreover, a hernia containing the ileum, appendix, caecum, and ascending colon in adults has been described as a giant Amyand hernia [9]. Similar to incarceration, the degree of inflammation of the appendix does not change the definition [10].

Incidence

The exact incidence of AH varies greatly by geographic area and appears to be undetermined, as most cases occur in developing countries without further reporting. The analysis of 83 pediatric case reports (n = 182) provided an approximate overview of the worldwide reports of AH (Fig. 2). The distribution of cases of AH by parts of the world is contradictory evidence of its predominance in Asia and Africa, but there is not enough data to refute a simple correlation between the incidences of AH and inguinal hernia in general. This seems logical given the population sizes and possible underreporting of AH.

Fig. 2

Global pediatric Amyand hernia case reporting over 2003–2023. No legend

Despite varying numbers of cases, most authors report similar AH rates. The incidence of Amiand hernia rarely ranges from 0.09 [10] to 1.7% [7, 8, 11, 12]. Thus, a pediatric surgeon can expect to find an appendix in 1–1.6 out of every 1000 hernia sacs [13]. A clinical serial study involving 21 cases in Turkey, where the highest number of AHs have been registered in the last 20 years, showed that the incidence of AH is also 0.97% [14]. Therefore, there is still no convincing population data on the demographic prevalence of AH. However, there are some reports pointing to a possible genetic predisposition. For example, Baldassarre et al. [15] reported two 32-day premature twins with simultaneous right-sided AHs, where a congenital band extending from the appendix into the scrotum to the right testicle in neonates has been suggested as a possible explanation.

There are also not many sources indicating on associated conditions. as undescended testis [16]. More rarely, an unusual left-sided AH may be associated with situs viscerus inversus, intestinal malrotation, or a cecum mobile [4, 17]. There is a suggestion that the caecum and appendix protrude through the left inguinal canal, either due to high caecal mobility, in these cases [5]. Therefore, the higher mobility of an appendix with or without caecum is one of the more popular etiologic theories rather a genetic predisposition [18].

The frequency of right-sided AH is so high that some authors state exclusively right-sided [5], however, there are many reports of cases of left-sided AH with previously noted associations [4, 5, 17, 18]. Moreover, some authors have found that the rate of left-sided AHs is between 4.3% [19] and 10% [20]. The distribution of AH between males and females varied significantly (Table 1) from reports of findings exclusively in boys [11, 19, 21, 22] to 16–25% of female AH in some case series [3, 6].

Table 1 Case series of Amyand hernia in children over the 2003–2023 period

Despite the fact that AH is recorded in all age groups [1], it is diagnosed three times more often in childhood, when it is associated with patency of the vaginal process and, therefore, more often indirect [25, 26]. Most cases of AH have been registered in premature newborns and young children [20]. According to the literature, the average age at which surgical correction of AH is performed ranges from 5 days after birth to 16 months [27]. In a series of cases in adults, the second peak of AH at about 70 years of age [28, 29] was found with a predominance of direct hernias.

The etiopathogenesis

The etiopathogenesis of AH is still disputable, as well as the role of compressive trauma to the appendix inside the hernial sac in the development of acute appendicitis [3]. It is noticed [30] that the appendix can be herniated in any abdominal wall hernias—inguinal, incisional, Spigelian, or umbilical. On the one hand, there is no evidence of a higher incidence of acute appendicitis associated with AH patients, on the other hand, there are relatively fewer cases of obstructive appendicitis in these patients [3].

Classification of AH

Losanoff and Basson proposed a classification of AH in 2007 [3, 8, 31], where AH without or with appendicitis is presented in the following subtypes:

Type 1 includes a normal appendix within the inguinal hernia

Type 2 includes acute appendicitis without inflammation

Type 3 includes acute appendicitis with inflammation of the abdominal wall or peritoneum

Type 4 includes appendicitis with concomitant abdominal pathology.

This classification was created to provide rationale for the further surgical technique in adults, mainly focused on the possibility of using a mesh depending on the degree of regional septic inflammation. However, some pediatric cases have been described using this classification [3, 8, 18]. The fact that almost all pediatric AH are indirect and require a different approach than in adults, in addition to the presence of a different spectrum of comorbidities, dictates the need for a different classification and strategy in pediatric surgery. Classification of AH in children according to presenting symptoms and inflammatory status of the appendix could help determine whether an appendectomy should be performed [19] and how to manage left-sided AH.

Difficulties before surgery

The rarity, abnormal and unexpected location of the vermiform appendix, and late admission with septic complications make the diagnosis and treatment of AH difficult. The clinical picture varies widely, but all cases can be divided into two groups: uncomplicated with a non-inflamed appendix—the majority of the cases [8] and complicated. Complications usually arise from late hospitalization and a pronounced inflammatory condition of the appendix within the hernial sac.

Uncomplicated AH has no defining features and initially manifests itself as an incarcerated or strangulated hernia without any additional features. Preoperative diagnosis of AH is very difficult and, as a rule, is an incidental finding during surgery due to various clinical manifestations and features [7, 21, 32]. However, while in some studies [20] none of the patients was diagnosed before surgery, other authors indicate that a thorough clinical examination and various instrumental studies made it possible to establish a preoperative diagnosis in a large percentage of cases, especially in children older than one year [6, 14, 32]. Preoperative diagnostics provide information to parents of patients about AH and preoperatively prepare the surgeon for precise treatment [14].

Ultrasonography is considered the most effective and justified instrumental method. First, inguinoscrotal ultrasonography can detect the appendix within the hernial sac as an incarcerated tubular structure [6, 33]. Some authors [6, 14] point to the relatively high sensitivity of ultrasound in the preoperative diagnosis of AH. So, M. Okur et al. [14] report that AH can be detected by ultrasound in 42.8% of patients before surgery if the sonographer is aware of this condition. Secondly, ultrasound is useful for differential diagnosis and can detect other acute conditions testicular torsion [27] and acute epididymitis [34], which in the early stages can mimic AH.

Less commonly, CT was used to diagnose AH. Rather in complicated cases than routinely [7, 14, 20], due to exposition to radiation and extra cost. It is considered more justified in left-sided AH, but in most cases, it is performed after surgery to exclude malrotational abnormalities or situs viscerus inversus. An abdominal X-ray can be used to demonstrate the presence of gas in the groin area in the case of a strangulated hernia, signs of intestinal obstruction, or perforation of a hollow organ in the case of severe ischemia [27]. There are also sporadic data on the use of upper gastrointestinal contrast to confirm normal bowel rotation in left-sided AH [5].

Most of the complications of AH are septic in nature and in the advanced stage cannot indicate AH itself as the root cause. The primary cause of these changes in most cases is appendicitis within the hernial sac, which is not typical for AH and, according to literature develops in 0.07–0.13% [6, 28, 35]. However, some studies [14, 20] demonstrate a higher incidence of up to 16.6% of inflamed appendixes among patients with incarcerated AH. This fact fuels controversy about the relationship between the strangulation of the appendix in the inguinal canal and the development of its inflammation [36]. Some authors [14] believe that once the appendix enters the sac, it becomes vulnerable to injury, which, in turn, results in blood supply interruption or significant reduction, leading to inflammation and appendiceal obstruction.

The indirect course of the hernia makes it possible to communicate with the inguinal canal and scrotal cavities. That explains many cases of abdominal wall abscesses or scrotal pyocele (scrotal abscess) [23, 26, 37,38,39,40], scrotal [41] or right groin entero-cutaneous fistula [42], pneumohernios due to the rupture of the caecum [43]. Cases with varying degrees of septic lesions of the spermatic cord and testis have also been published, ranging from ischemic inflammation [34] to necrosis followed by removal of the structures [44, 45]. The AH manifestation as acute scrotum without hernia bulge is possible in neonates [46] and should be included in differential diagnosis among infants. The spread of the septic process into the abdominal cavity can lead to the formation of an abscess of the abdominal cavity on the background of the perforation of the appendix into the inguinal hernia [47, 48]. There are also many reports of necrotizing fasciitis of the anterior abdominal wall secondary to caecal perforation or appendicitis in AH patients [45, 49,50,51]. In cases of caecal involvement, signs of intestinal obstruction are also present [18].

Difficulties during the surgery

Surgical treatment of AH can be challenging if it presents as an incidental finding or complicated. The best strategy is debatable and, according to the literature [14, 20, 52,