Enterolithiasis is the presence of an enterolith within the intestinal lumen and is a rare condition; its prevalence in selected populations varies widely from 0.3% to 10% because it is largely dependent upon clinical presentation, etiology, and underlying risk factors [1, 6]. Enteroliths are defined as endogenous foreign bodies in the gastrointestinal tract [2]. Enteroliths are classified into primary and secondary types [1]. Primary enteroliths are defined as concretions that develop inside the bowel. In contrast, secondary enteroliths form outside the gastrointestinal tract and migrate into the bowel accompanied by fistulation to the intestinal lumen, which is similar to that observed in cholelithiasis or urolithiasis [1]. Furthermore, primary enteroliths are subdivided into “true” and “false” subcategories [1, 2]. Clinically, true enteroliths are extremely rare, whereas false enteroliths are much more common in primary enteroliths [1, 9,10,11]. False primary enteroliths are composed of orally ingested indigestible matter, such as feces (fecaliths), hair balls (trichobezoars), vegetable matter (phytobezoars) or other exogenous substances, such as varnish and barium sulfate [1, 6]. Conversely, true primary enteroliths are defined as stones made of precipitants and/or deposits that normally exist in the intestine, such as choleic acids and calcium salts [1, 2]. The composition of true primary enteroliths is closely related to their location. Choleic acids precipitate under lower pH conditions, so enteroliths formed in the duodenum and jejunum are mostly composed of choleic acid, which is largely affected by significant diverticular disease, strictures, or stenosis [2, 6]. In contrast, calcium salts are soluble in water and acidic environments; thus, they precipitate under alkaline pH conditions in the distal small intestine or colon, most commonly in the terminal ileum [2]. With regard to the mechanisms contributing to the formation of enteroliths, two factors are considered. The first comprises mechanical factors, such as intestinal stasis due to intestinal diverticular diseases [12,13,14,15]; blind pouches after side-to-side enteroanastomosis [16, 17]; blind loops including the afferent loop in Billroth-II gastrojejunostomy and Roux-en-Y reconstruction [18,19,20,21]; incarcerated hernias [8]; intestinal kinking from intra-abdominal adhesions [8]; and intestinal strictures and stenosis encountered in infectious and inflammatory conditions, such as Crohn’s disease [8], ulcerative colitis [8], intestinal tuberculosis [22, 23], and, rarely, radiation enteritis [7, 8]. By contrast, the second factor involves chemical properties, such as acidic conditions. Impaired intestinal flow and stasis in the gastrointestinal tract may promote microbiome overgrowth-accelerated changes in the pH of the surrounding bowel contents, resulting in precipitation of substances out of solution [6]. In our case, the concretions were almost completely composed of DCA, that is, true primary enteroliths of the choleic acid type, and the location was the distal jejunum (as in many reports). The radiological diagnosis of enteroliths depends on their calcium content [8]. Enteroliths containing a higher proportion of calcium salts are more radiopaque and form in the relatively more alkaline environment of the distal ileum. Choleic acid enteroliths are more radiolucent and form in the more acidic environment of the proximal small intestine [6]. In the present case, the enteroliths were radiolucent, were not detected on abdominal X-ray, and appear as slightly high-density matter exclusively on abdominal CT. Only a few studies have reported that true primary enteroliths may occasionally have a central “fruit pit”, such as that from a plum [1, 2, 6]. Some enteroliths of the present case also contained a fruit seed-like component in their nucleus. These pits were presumed to be persimmon seeds based on their appearance, which is exceptionally unique. Upon our inquiry, the patient reported no memory of ingesting persimmon seeds in the past.
Radiation enteritis is a rare cause of enterolithiasis. A literature search of the PubMed database analysis yielded 4 results published between 1962 and 2020 when searching for “enterolith AND radiation enteritis”. Excluding nonrelevant results and limiting the scope to articles written entirely in English, only 2 reports describing enterolithiasis associated with radiation enteritis were identified [7, 8]. In our case, there were multiple stenotic lesions derived from histopathologically evidenced radiation enteritis in the jejunum, and several true primary enteroliths had been fixed in each lumen immediately proximal to the strictures. These findings suggest that the stagnation of intestinal flow leading to the formation of enteroliths was caused by the thickening and narrowing of the small intestine associated with radiation enteritis. Even in this respect, the present case is extremely rare. In addition, the finding of “frozen pelvis” is often caused by subacute or chronic generalized peritonitis, including the result of NOM; however, in our case, we hypothesized that the frozen pelvis was derived from radiation therapy in the past because the fluid collection did not spread throughout the entire abdominal cavity but localized to the right paracolic gutter from the beginning of onset.
Small bowel obstruction is a common surgical presentation. Nevertheless, as Nonose et al. [24] described only 41 cases reported up to 2011, primary jejunal enterolithiasis uncommonly results in mechanical obstruction of the small intestine, which is known as enterolith ileus or pseudogallstone ileus. In the present case, it is reasonable to hypothesize that true primary enteroliths caused ileus prior to small intestinal perforation, which is also rare. Consistent with this concept, NTPSI, which is defined as small intestinal perforation excluding perforated duodenal ulcers and perforation due to external hernias and primary ischemic events, is a rare entity with an incidence reported in the literature of one case per year per 300,000 to 350,000 individuals [3,4,5]. Accordingly, NTPSI due to enteroliths has been occasionally reported, but is an exceedingly rare complication; thus, the incidence is difficult to quantify [6]. The reported causes of enteroliths resulting in NTPSI are mainly duodenal diverticulum [25], Meckel’s diverticulum [12], jejunal diverticulum [26, 27], and Crohn’s disease [28], but there are no reports relevant to radiation enteritis. Thus, to the best of our knowledge, this is the first case of NTPSI caused by multiple true primary enteroliths associated with radiation enteritis, and the hypothesized pathophysiological chart is shown in Fig. 6.
The mortality of NTPSI was reported to range from 15 to 39% in the early era because surgery was often delayed due to difficulties experienced with the initial diagnosis of the precise cause and site of perforation [3,4,5, 29]. However, the recent literature has demonstrated that the mortality rates might be lower than those in the past [3]. One reason may be the development of modern imaging modalities, particularly CT. CT imaging currently substantially aids the evaluation of a suspected perforation and is demonstrated to be accurate in defining the possible site of the perforation [5]. Once NTPSI is diagnosed, urgent surgical intervention is typically required [3,4,5, 30]. Jain et al. [30] mentioned that the appropriate operative procedure for NTPSI depends upon the presence or absence of adverse conditions in the patient, such as hypotension, a long perforation-to-operation interval, a high volume of peritoneal contaminant fluid, and/or an edematous bowel not available for repair. For patients with adverse factors, the no suture line-in procedure, such as ileostomy, seems to be better [30]. In our case, localization of fluid collection induced by frozen pelvis and intra-abdominal drainage repressed the typical symptoms of peritonitis and stabilized her general condition. Therefore, we continued NOM given that we judged a low need for surgery, and we could not deny that the NOM alone may cure her condition. Furthermore, we hesitated to perform surgery because we could not identify the accurate perforation site and we could not deny the possibility of duodenal perforation and leakage of refluxed jejunal juice via the perforation site. Consequently, the time between onset and surgery was 11 days. This finding is consistent with the difficulty of preoperative diagnosis of NTPSI, as reported in previous studies [3,4,5, 29]. As a result of performing CT up to five times, an accurate diagnosis of NTPSI was finally made. A large perforation site and an incarcerated stone hypothesized to be the cause of perforation were identified; therefore, we decided to perform an ileostomy for this patient given the presence of adverse factors, such as a long interval between onset and operation, a large amount of intraperitoneal contamination, and small intestinal edema.
