Abstract
An abdominal mass was identified upon palpation of the abdomen in a normal, asymptomatic, 1-year-old female domestic shorthair cat presented for elective ovariohysterectomy. Radiographic and ultrasound examinations demonstrated a well-circumscribed caudal abdominal mass. Ultrasound guided needle aspiration cytology was consistent with an accumulation of squamous epithelial cells. The mass was associated with the jejunum and was excised via resection anastomosis of the intestinal segment after ovariohysterectomy. Histologic examination provided the diagnosis of an intestinal duplication lined with epithelium typical of that in the esophagus. The cat recovered without complications.
A 1-year-old female domestic shorthair cat was evaluated prior to an elective ovariohysterectomy. The cat had been in heat 3 weeks before presentation. A round, freely moveable, non-painful, 3 cm abdominal mass was identified on physical examination. A complete blood count was normal. Abdominal radiographs demonstrated a well-circumscribed soft tissue mass cranial to the urinary bladder. Ultrasound examination identified minimal peritoneal effusion and a well-encapsulated mass in the left caudal abdomen adjacent to but not part of the small intestine. The mass was inhomogenous and demonstrated multiple, focal, hyperechoic areas with posterior shadowing. It had no discernable layers, and no abnormalities were identified in the reproductive tract or other abdominal organs. Fine needle aspiration was performed with ultrasound guidance, and cytological examination was consistent with large, anuclear squamous cells.
Exploratory laparotomy identified the mass on the mesenteric surface of the mid-jejunum and shared its blood supply. A resection anastomosis of the affected segment was performed after ovariohysterectomy. After removal from the surgical suite, the jejunum was incised longitudinally along its antimesenteric border, there was no communication with the mass. Incision of the mass produced a gross exudate and revealed the mass to be hollow. The cat recovered well from surgery and was discharged from the hospital 2 days later. Aerobic and anaerobic cultures of the exudate were negative. The owner reported that the cat was normal upon suture removal 2 weeks later.
Histologic sections of the intestine and cross sections through the cyst showed that the wall was continuous with the smooth muscle of the small intestine and it contained all of the normal layers of the gastrointestinal tract. The tunica muscularis of the duplication was composed of two layers of smooth muscle oriented at angles to one another. Most of the luminal surface was devoid of epithelium, but there were multiple short strips of non-keratinizing, stratified squamous epithelium similar to those of the esophagus (Fig 1).
Masson's trichrome stained cross section through the point of attachment of the cystic mass to the small intestine. Smooth muscle stains red and collagen stains blue. In this area the lumen of the duplication is ulcerated and completely devoid of mucosal epithelium. The different layers are: cyst lumen (CL), small intestine lumen (SIL), small intestine mucosa (SIM), lamina muscularis mucosae (MM), tunica submucosa (SM), inner layer of smooth muscle of the tunica muscularis (ISM), and the outer layer of smooth muscle of the tunica muscularis (OSM). Bar=0.5 mm.
Intestinal duplications are rare congenital anomalies that have been reported in people, dogs, cats, horses, cattle, and goats (Ablin et al 1991, Gaughan et al 1992, Otiang'a-owiti et al 1997, Stern and Warner 2000). They can occur anywhere along the gastrointestinal (GI) tract from the tongue to the rectum (Stern and Warner 2000).
This case demonstrated all three characteristics of an intestinal duplication: an intimate association with the GI tract, a well developed smooth muscle layer, and an epithelial lining (Berrocal et al 1999, Qi et al 2001). Duplications may be classified by shape, vascular supply, or location (Li et al 1998, Stern and Warner 2000). This mass was spherical, occurred on the mesenteric side of the intestinal tract, and did not communicate with the adjacent GI lumen. These characteristics are classical for cystic duplications (Stern and Warner 2000). Enteric duplications contain all four layers of the normal GI tract—mucosa, submucosa, muscularis, and serosa (Berrocal et al 1999, Vijayaraghavan et al 2002)—as did the mass in this case, with a portion of the muscularis shared with the normal, adjacent bowel. The mucosa in duplications may be the same as that of the adjacent bowel, heterotopic gastric mucosa, or respiratory in character. The presence of heterotopic gastric mucosa is reported to be associated with ulceration of adjacent bowel leading to perforation and hemorrhage (Stern and Warner 2002, Arbell et al 2002). The mucosal lining of the case reported here, where present, was most like that of the esophagus. Neither inflammation nor gastric glands were identified on this segment, making ulceration secondary to heterotopic gastric mucosa an unlikely cause of mucosal loss. The accumulation of epithelial cells in the lumen of the duplication, however, may have led to pressure necrosis of the mucosa (Berrocal et al 1999).
Vascular patterns have also been used to classify intestinal duplications and include parallel, or type I, and intramesenteric, or type II (Li et al 1998). Type I duplications have an arterial supply parallel to that of the adjacent bowel and may have a separate mesentery (Ia), a common mesentery with no shared intestinal wall (Ib), or a shared mesentery and partially shared wall (Ic) (Li et al 1998). Type II duplications are located within the mesentery supporting the adjacent bowel and may not (IIa) or may (IIb) share a portion of its muscular wall (Li et al 1998). The duplication in the cat described here did not have a separate, or parallel, blood supply, shared a wall with the adjacent jejunum, and was classified as a type IIb duplication (Fig 2).
The blood supply of the duplication in Fig 1 is intimately shared between the cyst and adjacent jejunum (A). A separate, or parallel blood supply is not evident (B).
Classification by location in people determined ileal duplications to be most common, followed by esophageal (Arbell et al 2002). Esophageal duplications in people, unlike the cat in this report, are located in the thoracic cavity (Stern and Warner 2000). Lower gastrointestinal duplications (eg, colon, rectum) may be accompanied by urogenital tract anomalies, and duplications anywhere in the GI tract may be accompanied by other GI tract anomalies (48%) or concurrent vertebral anomalies (21%) (Stern and Warner 2000). No vertebral anomalies were noted on the abdominal radiographs made in this case, and no other lesions were identified on abdominal exploratory. Thoracic radiographs were not performed.
The location of the duplication also determines the associated clinical signs. Abdominal enlargement, abdominal pain, partial or complete GI obstruction, melena, hemorrhagic shock, peritonitis, and sepsis have been reported (Stern and Warner 2000, Arbell et al 2002). Intestinal duplications are commonly diagnosed in young people; up to 85% are diagnosed by 2 years of age (Stern and Warner 2000). They are considered benign lesions in young people and may be an incidental finding as in the cat described here (Stern and Warner 2000, Fletcher et al 2002). Significant complications, such as ulceration, GI hemorrhage, perforation, peritonitis, intestinal obstruction, intussusception, or intestinal volvulus also occur more often in younger patients (Stern and Warner 2000, Arbell et al 2002). Neoplastic transformation of a clinically silent duplication can occur later in life, resulting in signs caused by the presence of an abdominal mass in older people (Fletcher et al 2002).
Diverticular malformations have been described in 13 dogs and four cats in one report (Ablin et al 1991). Age at presentation of the cat in this report was different from dogs, which ranged from 2 months to 10 years of age, but similar to the cats (4 months to 2 years) in that study (Ablin et al 1991). Clinical signs were absent in two of the four cats and two of 13 dogs (Ablin et al 1991). Two dogs with infected diverticular malformations presented acutely, and one malformation was identified incidentally in another dog (Ablin et al 1991). The most common location was antimesenteric in 70% of the cases, which differs from that in people and the case described in this report (Ablin et al 1991).
The diagnosis of intestinal duplications is primarily based on radiographic identification of a mass and ultrasound examination (Berrocal et al 1999, Stern and Warner 2000). Contrast studies are usually negative (Stern and Warner 2000) while ultrasound can provide a definitive diagnosis in cases of suspected intestinal duplication if the mass lesion demonstrates features of the GI tract (Geller et al 1995, Vijayaraghavan et al 2002). The luminal border is hyperechoic, the muscular wall is hypoechoic, and the serosal layer and adjacent fat are hyperechoic (Simonovsky 1996). The case described here lacked distinct layers most likely due to the lack of consistent epithelium and thick exudate within the lumen. A duplication cyst that does not exhibit typical GI tract wall structure or association with the GI tract on ultrasound may be evaluated with computed tomography or magnetic resonance imaging (Berrocal et al 1999, Stern and Warner 2000). Laparoscopy has also been advocated for diagnosis followed by assisted or open excision (Schleef and Schalamon 2000).
The owner of the cat in this report declined further diagnostic evaluation before surgery, and the abdominal approach was extended to allow evaluation and excision of the mass. Treatment of intestinal duplications consists of complete excision whenever possible in all species (Stern and Warner 2000). The prognosis in dogs and cats is considered excellent if perforation had not occurred (Ablin et al 1991). Complete excision was possible in this case and was performed to avoid the future complications such as obstruction, perforation, and potential malignant transformation.