The annular pancreas (AP) is a rare congenital anomaly characterized by pancreatic tissue partially or completely encircling the second part of the duodenum. This results from the aberrant migration of the ventral pancreatic bud during embryogenesis. This condition was first described by Tiedemann in 1818 and later termed “annular pancreas” by Ecker [¹]. Between the fourth and eighth week of embryonic growth, the pancreas typically forms through the rotation and merging of the dorsal and ventral pancreatic buds, driven by the duodenum’s expansion. Thereafter, the ventral bud gives rise to the lower portion of the pancreatic head and the uncinate process, while the dorsal bud develops into the body and tail of the pancreas [²]. The majority of cases of AP are identified in the pediatric population, exhibiting signs of gastric outlet obstruction [³]. Common symptoms in adults include abdominal discomfort, vomiting, and hematemesis in patients [⁴]. A recent population-based study in the United States analyzed data from 6,162,600 patients who underwent abdominal imaging, identifying 210 cases of AP. This finding suggests an estimated prevalence rate of 3.4 per 100,000 individuals [⁵]. It impacts both sexes, with a modest predominance towards males [⁶]. The current standard for diagnosing AP relies on abdominal imaging techniques, including ultrasound, computed tomography (CT) scans, barium studies, endoscopic retrograde cholangiopancreatography (ERCP), and magnetic resonance cholangiopancreatography (MRCP) [⁷]. Approximately 40% of cases necessitate surgical interventions, such as duodenoduodenostomy or duodeno-jejunostomy, to circumvent the blocked duodenal section. Pancreatoduodenectomy is advised only in instances where the AP coexists with pancreatolithiasis and is further complicated by chronic pancreatitis [⁴]. This report condenses a meticulous review of 24 recently published case reports (2018–2024), providing a contemporary overview of symptomatic adult AP, along with a case report that further contributes to its clinical significance.

This paper aims to advance the understanding of AP presentation in adults, a rare condition with limited published research. Through a case report and a comprehensive literature review, we seek to provide valuable insights that enhance the current knowledge of this pathology.

A 50-year-old male presented to the outpatient clinic with chief complaints of vomiting and abdominal pain for 3 weeks. The pain was intermittent, moderate to severe in intensity, poorly localized in the upper abdomen, radiating to the back, and was relieved by vomiting. There was a history of projectile bilious vomiting associated with post-prandial abdominal pain and fullness for 3 weeks. The patient also had a history of chronic smoking and alcohol intake for 20 years. There was no history of weight loss, fever, or melena. There were no co-morbidities associated, including no history of diabetes mellitus, hypertension, tuberculosis, bronchial asthma, or epilepsy, and no significant past medical or surgical history was reported. There was no history of similar complaints in the past. On examination, the abdomen was distended and tender, along with guarding and rigidity. No mass was palpable per abdomen. No significant findings in per rectal examination.

Initial investigations, as detailed in , revealed slightly decreased hemoglobin levels, an elevated white blood cell count, elevated random blood sugar, and slightly deranged liver enzymes. Renal function tests were within normal limits. Electrolytes were slightly deranged, and pancreatic enzymes were highly elevated. Viral markers, including HCV, HBsAg, and HIV, were non-reactive.

Further, the patient was investigated, and a CT scan of the abdomen revealed an abnormal configuration of the head of the pancreas with features suggestive of (F/S/O) chronic calcific pancreatitis (CCP) and a triangular segment of the pancreatic tissue encircling the second part of the duodenum (D2), causing complete obstruction. A few foci of calcification were also noted in the head of the pancreas (HOP) along with stranding of peripancreatic fat and dilated pancreatic duct with no evidence of malignancy or necrosis .

Based on the diagnostic findings, surgical intervention was planned. The patient underwent pylorus-preserving pancreatoduodenectomy under general anesthesia with endotracheal tube intubation. After proper painting and draping, a nasogastric tube was inserted for gastric decompression. An extended right subcostal incision was given to access the abdominal cavity. Intraoperatively, the first part of the duodenum (D1) was found to be dilated , with annular pancreatic tissue encircling the second part (D2), causing its narrowing ) – findings consistent with the preoperative radiological imaging findings. Intra-operatively, a mass-forming lesion was palpated in the HOP. A stapler was fired along the distal part of the stomach, and another was fired approximately 20 cm distal to the ligament of Treitz. A jejunal loop was then brought up retrocolically, and an end-to-side anastomosis was performed, resulting in pancreatojejunostomy, hepaticojejunostomy, and gastrojejunostomy. The specimen was then resected, and the area post-resection was visualized. The macroscopic inspection of the gross specimen by observing the cut section revealed the presence of a stone in the HOP (pancreatolithiasis) . The postoperative course was uneventful, with mild abdominal pain and minimal serosanguinous discharge from the drain. The patient was discharged on postoperative day 7 in a stable condition.

Microscopic examination of the resected specimen revealed chronic inflammatory infiltrates with interlobular fibrosis, confirming the diagnosis of chronic calcific pancreatitis. Pancreatic duct dilation and pancreaticolithiasis were noted without evidence of dysplasia or malignancy.

At 6-month postoperative follow-up, the patient remained asymptomatic with complete resolution of vomiting and abdominal pain. No signs of recurrence or complications were observed on CT imaging and labs.

All procedures performed in this study adhered to the ethical standards of the institutional and national research committee and the Helsinki Declaration. Informed written consent was obtained from the patient for the publication of this case report and accompanying images. No identifiable patient information is included in this publication. Ethical approval was waived by the Institutional Review Board (IRB) for the case reports.

AP is a rare congenital anomaly resulting from an embryological error during the fifth to seventh weeks of gestation, wherein the ventral pancreatic bud fails to rotate properly, leading to partial or complete encasement of the duodenum. This case illustrates the elusive nature of the condition, consistent with historical autopsy-based prevalence estimations of approximately 1 in 20,000, although more recent radiological studies suggest higher rates [⁸]. These discrepancies underscore the underrecognized burden of AP, particularly in adults, where incidental diagnoses often mask symptomatic presentations. In our patient, the diagnosis of AP with CCP highlights the clinical challenges posed by its nonspecific symptoms—most commonly abdominal pain, nausea, and vomiting, and less frequently hematemesis. In a large single-institutional cohort study, Nagpal et al. [⁹] reported that 59.6% of adults with AP were asymptomatic; among symptomatic patients, abdominal pain was the most frequently observed symptom (50%).

To better contextualize our case and understand current trends, we conducted a structured literature review focusing on adult patients with symptomatic annular pancreas who underwent surgical intervention, particularly pancreatoduodenectomy. This review aimed to compare presenting symptoms, diagnostic modalities, and treatment approaches in recently reported cases.

A structured literature review was performed using PubMed and Scopus databases, covering the period from 2018 to 2024. The following Boolean keyword string was applied: (“Annular pancreas” OR “pancreatic ring”) AND (“adult” OR “adult presentation”) AND (“case report” OR “case series”). Filters included: English language, human studies, and adult subjects (aged 18 years or older). The review process was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to ensure transparency, reproducibility, and methodological rigor. A PRISMA flow diagram detailing the selection process has been included to summarize the article screening and inclusion process.

A review of recent case reports confirms that AP remains a rare condition, often undiagnosed in asymptomatic individuals. Symptomatic patients typically present with abdominal pain and vomiting, though additional symptoms such as weight loss and early satiety may also occur. Abdominal imaging serves as the cornerstone of diagnosis, with CT scans being the most commonly employed modality to confirm the condition. Asymptomatic cases of AP generally require no intervention and are managed conservatively. In contrast, surgical treatment is the primary approach for symptomatic patients, with the specific procedure tailored to the individual’s anatomy and the severity of the pathology. Further timely research is needed to establish standardized protocols for the diagnosis and management of AP.