Asymptomatic Enteric Duplication Cyst in a Geriatric Cat: Case Report and Review of the Literature

Introduction

Enteric duplication cysts (EDCs) are rare congenital malformations that originate from the alimentary tract and share a common blood supply; they are tubular or spherical structures that can arise anywhere along the digestive tract from the oral cavity to the rectum and can be communicating or noncommunicating with the enteric lumen.^1–3 There are very few reports of EDCs in the veterinary literature, and they frequently present with nonspecific clinical signs, posing a diagnostic challenge. The aim of this article is to report a duodenal duplication cyst in an adult feline patient and review the available literature on this topic to formulate diagnostic and treatment recommendations based off current knowledge.

Case Report

An 11 yr 7 mo old 5.1 kg female neutered domestic shorthair was presented for an asymptomatic abdominal mass detected approximately 8 mo previously during a routine appointment. The cat was also diagnosed with chronic kidney disease International Renal Interest Society stage II.⁴ At presentation, the cat was bright and alert but was described to be polydipsic and polyuric. Physical examination was unremarkable aside from a nonpainful, elongated, firm mass palpated in the cranial abdomen.

A complete blood cell count was unremarkable. Serum biochemistry revealed mild azotemia (blood urea nitrogen 88.8 mg/dL, reference interval 15–59.4; creatinine 2.09 mg/dL, reference interval 0.9–2.3) and mild hypercholesterolemia (187.6 mg/dL, reference interval 84.9–154). Total thyroxine and coagulation profile were unremarkable. Urinalysis was unremarkable with a urine specific gravity of 1.015; however, bacteriology from a cystocentesis sample yielded a heavy growth of hemolytic Escherichia coli. Urine protein-to-creatinine ratio was within normal limits (0.19, normal <0.2), and mean Doppler systolic blood pressure was 164 mm Hg.

Computed tomography (CT) revealed a large (˜6 cm length × 4.2 cm at the base and 2.2 cm at the top), complex cystic structure with a homogeneously contrast-enhancing outer wall of medium thickness (˜2–3 mm) occupying the right side of the abdomen (Figure 1). The entire structure was irregular in shape and the content was hypoattenuating and nonenhancing. The mass was in direct contact with the caudal part of the descending duodenum, with a subjectively intact duodenal wall. There was no visible connection between the cystic and duodenal lumen. Both kidneys were small and irregular in shape with mineralization of the renal crest. The rest of the abdomen and thorax was otherwise unremarkable.

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To further characterize the cystic mass, a focal ultrasound examination was performed and revealed an enlarged, multipocketed structure with hypoechoic luminal contents in close proximity to the duodenum. The surrounding duodenum was normal, with intact wall thickness and layering. Based on the clinical examination and imaging findings, a presumptive diagnosis of an EDC was made, and surgical exploration was performed.

The cat was premedicated with 1 μg/kg dexmedetomidine^a, 0.2 mg/kg methadone^b, and 0.1 mg/kg midazolam^c intramuscularly. Induction was performed with alfaxalone^d IV to effect, and the cat was intubated and maintained with inhaled isoflurane^e in 100% oxygen. A ventral midline coeliotomy was made and the proximal duodenum isolated. The mass was originating from the anti-mesenteric border of the proximal duodenum at the level of the right limb of the pancreas. It was irregular in shape, elongated and cystic; fluid was aspirated and submitted for cytology and bacteriology. Initial dissection revealed the mass and duodenum to share the serosa and muscularis, although with separate, intact submucosal and mucosal layers. The mass was firmly adhered to the duodenum but was not communicating with the duodenal lumen. An en bloc resection of the mass with omentalization was performed without small intestinal resection. The pancreatic lymph node was subjectively enlarged and darker in appearance and was also excised. The cystic mass and lymph node were submitted for histopathology. The abdomen was lavaged with sterile saline and closed in a routine manner.

The cat recovered uneventfully from surgery and analgesia was continued with 0.02 mg/kg buprenorphine^f IV q 8 hr. Antibiosis was provided perioperatively with 20 mg/kg cefuroxime^g IV. The cat was discharged 48 hr after surgery with 1 mg/kg telmisartan^hper os q 24 hr, and a 14 day course of 20 mg/kg amoxicillin/clavulanic acidⁱper os q 12 hr based on the urine bacteriology results. Cytology of the aspirated contents demonstrated proteinaceous fluid with possible mucinous material, consistent with a cystic lesion. No atypical cells were seen, and culture yielded no bacterial growth. Examination of the fixed surgical specimen revealed that the structure was irregularly L-shaped, 6 × 2.5 × 2.3 cm (smallest diameter) to 3.4 cm (largest diameter), pale tan and cream-colored, and multi-cystic, with 2- to 4-mm-thick walls (Figure 2A). Histopathology revealed a multicystic lesion with distinct compressed layers reminiscent of duodenal wall. This was described in the following centripetal manner: (1) an external serosa and adventitial layer, (2) two layers of smooth muscle (longitudinal and transverse) with blood vessels and rare scattered myenteric plexuses (Auerbach’s plexuses), (3) a submucosa layer with connective tissue, smooth muscle cells, and rare submucosal plexuses (Meissner’s plexuses), (4) a frequently present muscularis mucosae, (5) a lamina propria, and (6) a ciliated simple cuboidal mucosa epithelium, with no villus structure formation observed. Within the lamina propria, multifocal crypts of embedded pseudostratified cuboidal mucosa epithelium were observed (Figures 2B–E). The histological appearance, along with the surgical and imaging findings, was diagnostic for an EDC. The lymph node was reactive with no evidence of neoplasia or gross inflammation.

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At an 8 mo postoperative check, the cat was asymptomatic with no signs associated with gastrointestinal disease or recurrence.

Discussion

A definitive diagnosis of an EDC must fulfill previously defined criteria: (1) the EDC should have an epithelial lining that resembles that of the gastrointestinal tract; (2) the EDC is an empty, cystic structure that consists of a muscular coat, usually two distinct layers; (3) the EDC should extend alongside a portion of the alimentary tract and be firmly attached to it; (4) the type of epithelial lining of the duplication is not necessarily consistent with that part of the gastrointestinal tract to which it is attached.^5,6

Enteric duplication cysts have been described in humans with an estimated prevalence between 1 in 4500 and 1 in 10,000, whereas in animals they have been described in dogs, cats, horses, and goats; however, the real prevalence in both human and veterinary medicine is unknown owing to the rare nature and nonspecific symptoms associated with this pathology.^1,7–19 Their etiology remains elusive in both humans and animals: many theories have been postulated, but none explain the whole spectrum of this anomaly.^3,19,20

The majority of cases reported in veterinary medicine are young animals, and this is in accordance with the human literature that report more than 80% of EDCs occur before the age of 2, presenting as bowel obstruction or an acute abdomen. However, a significant number of patients may not be diagnosed until adulthood.^19,20

The clinical presentation of an EDC is extremely variable depending on its location, size, shape, and effect on local tissue.^6,19,20 Frequently, patients are presented with vague clinical signs, mimicking other more common gastrointestinal pathologies, or they are completely asymptomatic with the EDC discovered incidentally. Most commonly, EDCs are diagnosed when secondary complications occur such as bowel obstruction, ulceration, perforation, bleeding, volvulus, or, rarely, malignant transformation.^6,19,20 In small animals, EDCs are usually associated with anorexia, depression, abdominal mass/distention, and vomiting, but they can also be asymptomatic representing an incidental finding.^1,8–16

In the veterinary literature, only nine feline cases (including this report) have been described and seven were symptomatic, being presented for signs consistent with obstruction or obstipation, including vomiting, anorexia, and tenesmus.^9–16 Only two cases, including the current case, presented for investigation of an asymptomatic abdominal mass.¹⁶

EDC location varies extensively between species: in humans, the ileum is the most commonly reported location (33%), followed by the esophagus (20%); in dogs, EDCs have been reported along the entire length of the intestinal tract; and in cats, the duodenum is the most common location reported in 5/9 cases.^{5,9–11,13,21} Other locations reported in cats include the esophagus, jejunum, colon, and rectum.^{11,12,14–16} EDCs in multiple simultaneous locations has also been reported in a cat (involving the duodenum and caudal esophagus).¹¹

Different imaging modalities have been used to diagnose EDCs.²¹ Abdominal radiography and contrast studies are usually nonspecific, whereas ultrasonography is the most common imaging modality used to diagnose EDCs.^9,21,22 The classic sonographic appearance consists of a double-layered cyst wall with an inner hyperechoic mucosal layer and an outer hypoechoic muscularis layer, also described as a muscular rim sign.^7,9 However, given the often-irregular shape, the nonuniform circumferential wall thickness of the cystic mass, and the presence of ingesta-related artifacts, this can be difficult to fully evaluate.²¹

Radiography and/or ultrasonography alone were used in 4/9 reported feline EDC cases, whereas 5/9 also used contrast-enhanced CT; in one case, no diagnostic imaging techniques were discussed.¹⁴ The most common radiographic findings reflect the human literature—soft tissue opacity masses demonstrating border effacement and/or a mass effect on adjacent abdominal contents—whereas ultrasonography routinely described a cystic mass with hypoechoic contents closely associated with the adjacent intestine.

CT and MRI are now routinely used to define the precise anatomical location and vascular communication between organs and can be helpful in complicated cases that benefit from a multiplanar approach.^9,21

In our patient, the CT scan accurately described the location, extent, and global appearance of the mass and greatly enhanced the ability to surgically plan preoperatively. Additionally, given the unknown nature of the abdominal mass at presentation, it provided full body staging in case of neoplastic disease as well as checking for unrelated concurrent disease or other associated anomalies of the urinary tract, genitalia, and lower spinal malformations previously associated with EDC.⁶ The CT appearance of EDC has been accurately described in humans and cats as smoothly marginated, fluid-filled cystic or tubular structures with thin, slightly contrast-enhancing walls that are adjacent to or communicating with the wall of the associated gastrointestinal tract, and the imaging findings of this case are consistent with the current literature.^9,23

The benefits of preoperative cytology of EDC contents in human medicine is controversial.²⁴ Although some authors recommended its use in helping obtain a definitive diagnosis and rule out malignant cystic transformation prior to further treatment, adverse events following fine-needle aspiration (FNA) have been reported, most notably the introduction of infection, which has been reported to be as high as 14%.^25,26 Cytology of aspirated cystic fluid was performed in 6/9 reported feline cases, with the majority describing a population of degenerate neutrophils and mixed squamous or mesothelial cells. The fluid was nondiagnostic in only one case and was strongly suggestive of neoplastic transformation of the cystic mass in another.^10,15 Current human recommendations are for FNA of EDC contents when there is concern of misdiagnosing more sinister lesions and for avoiding its use when there is a high index of suspicion of an EDC based on the imaging findings.²⁴

Management of symptomatic EDCs in human patients involves an en bloc resection of the cystic mass and adjacent viscera, or excision without intestinal resection if the cystic lesions are small and no compromise of blood flow to the adjacent intestinal segment is present.^6,27 To date, no consensus on the management of the asymptomatic EDC has been established; however, elective surgery with excision of the EDC is recommended to avoid dangerous potential sequelae such as gastrointestinal obstruction, inflammation or infection, perforation, septic peritonitis, hemorrhage, or malignant transformation.^19,28 In cases of duodenal duplications in human patients, if the cyst is in close proximity to the biliopancreatic duct, total resection may require a pancreaticoduodenectomy, a procedure that can carry significant risks with high morbidity and mortality.²⁹ Similar concerns were raised with the location of the duplication in our patient, and this was a further reason a subtotal excision rather than intestinal resection was performed.

As previously reported, careful surgical excision and omentalization of an EDC should be curative; however, recurrence can occur if the cystic lesion is not completely excised leading to fluid reaccumulation.^11,15,16

In 6/9 cases of feline EDC reported in the current literature, subtotal excision (described as dissection of the mass away from the adjacent segment of intestine) was uneventfully performed. No complications or recurrence of clinical signs were reported in the postoperative period in four cases; however, in the remaining two cases, recurrence of the EDC at the previous surgical site occurred, one at the level of the esophagus and the other at the descending colon.^11,15 The esophageal cyst initially recurred 2 mo after surgery, with recurrence of the initial clinical sign of vomiting; extensive subtotal excision revision surgery was performed with repeat omentalization of the mucosal defect. The cat started vomiting again 10 mo after the second surgery with recurrence of the esophageal cyst confirmed. Revision surgery was again performed, although the cat died in the immediate postoperative period.¹¹ The colonic cyst recurred 44 mo after initial treatment, confirmed with repeat abdominal ultrasonography and CT. Repeat subtotal excision was performed, with histopathology of excised tissue supporting a diagnosis of congenital colonic duplication. The mass reoccurred 17 mo after the second surgery, and a third subtotal excision was performed, with histopathology again supportive of colonic duplication. Telephone conversations with the owners reported no recurrence of clinical signs at 12 and 18 mo after the third surgery.¹⁵ These cases are unique compared with human medicine, in which, as far as the authors can confirm based off literature searches, EDC recurrence has not been reported after excision. The current recommendation in human medicine to perform resection of the intestinal segment containing the duplication may explain why no local recurrence has ever been reported compared with the subtotal excision being performed in feline patients.⁶

In the remaining reported three feline cases, enterectomy and anastomosis were performed. In particular, one case had a portion of jejunum containing multiple focal EDCs; in another case, large atypical squamous cells were found on preoperative FNAs; and in the last case, a malignant transformation of the duodenal duplication cyst was suspected.^10,14,16 In this patient, the ultrasonographic findings showed a loss of normal layering and increased wall thickening of the cystic mass, classically associated with gastrointestinal malignancy.³⁰ Despite an enterectomy, clinical signs (vomiting) returned ˜3 mo later, recurrence of the neoplastic duplication at the previous surgical was confirmed by FNA, and the cat was euthanized.¹⁰

Malignant transformation is a rare but significant complication of EDCs in human patients.^19,31 Only a few cases have been reported, and adenocarcinoma was the most common neoplasm diagnosed.²⁰ In human literature, EDC of the small intestine is frequently the site of malignancy, followed by colonic and rectal duplications.²⁰ The prognosis is generally poor once malignant change has occurred as they are commonly diagnosed at an advanced stage with metastatic disease.²⁰ The potential for malignancy should always be considered in the decision-making process, in particular in the management of asymptomatic EDC cases in adult animals.¹⁹

Conclusion

EDC should be considered as a differential diagnosis for a cystic abdominal structure in close proximity to the alimentary tract in adult to senior cats, even though it is predominantly a juvenile condition. A confident diagnosis can be difficult without histopathology, although characteristic ultrasonographic changes can provide a high degree of suspicion. CT is a very useful modality to fully appreciate the lesion and for surgical assessment. In the absence of any imaging or cytological criteria of malignancy, complete dissection and omentalization of the EDC from the associated intestinal wall, rather than performing intestinal resection, may be a suitable surgical option with satisfactory long-term patient outcomes.