Stromal tumor on the serosal surface of small intestine masquerading as a seminal vesicle tumor

A gastrointestinal stromal tumor (GIST) in the small intestine falling into the rectovesical pouch (RP) can be easily misdiagnosed as a seminal vesicle tumor (SVT) in males. To our knowledge, below is the first case where a GIST in the small intestine masquerading as an SVT has been identified.

A 74-year-old male came to the urological department for a neoplasm in the right seminal vesicle (SV). After an abdominal physical examination, no positive signs were found. Then, during a digital rectal examination, an irregular hard and mobile mass was detected in the right SV. A further contrast-enhanced computed tomography scanning revealed an irregular cystic solid mass in the SV region (Figure 1A,B). The results indicated the mass possibly being an SVT or other tumors. Therefore, an exploratory laparotomy was performed. During the operation, found on the serosal surface of the small intestine 110 cm away from the ileocecal junction (Figure 1C,D) was an exophytic mass (measuring 11.8 × 9.7 × 5.4 cm), which fell into RP and pressed the back of the SV. Then, the small intestine where the tumor arose was partially resected. The histopathological analysis showed a spindle cell tumor (Figure 1E). The mass was stained positive for CD117 (+) and DOG1 (+) (Figure 1F,G) and negative for CD34 (−), S100 (−), Desmin (−) and was identified as a GIST in the small intestine.

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(A, B) Contrast-enhanced CT coronal and sagittal images showing a cystic solid mass in the right seminal vesicle area; the solid lesions of the tumor appeared obviously inhomogeneously enhanced. (C) A lobulated mass detected in the rectovesical pouch. (D) The lobulated mass arising from the small intestine. (E) Spindle cells arranged in fascicles and showing mild nuclear pleomorphism and rare mitotic activity (hematoxylin and eosin stain). (F) Immunohistochemical analysis showing the tumor being positive for CD117. (G) Immunochemical analysis showing the tumor being positive for DOG1. Black arrow: Small intestine; hollow arrow: tumor; white arrow: seminal vesicle. CT, Computed tomography

GISTs occur in 7–15 per 1,000,000 people per year, and 60% of GISTs occur in the stomach and 20%–30% in the small intestine.1 Clinical symptoms of GISTs in the small intestine are related to their location, size, and malignant degrees. GISTs in the small intestine are diverse in morphology and density, accompanied by bleeding or no bleeding, cystic change, or calcification.2 Imaging contributes to their detection.3 Immunohistochemical stains contribute to their identification, CD117 and DOG1 being the two most effective markers.4

When dropping into the RP, a GIST in the small intestine is easily misdiagnosed as an SVT. The main causes of misdiagnosis are as follows: (1) The clinical symptoms of patients with a GIST in the small intestine and an SVT are both nonspecific. GISTs may present with gastrointestinal bleeding and abdominal pain or no clinical symptoms at all.4 SVTs present with hematospermia, urinary or gastrointestinal symptoms, or no symptoms at all5; (2) urologists have fewer experience of identifying GISTs in the small intestine. A urologist may habitually consider a mass found in the SV region as an SVT; (3) GISTs in the small intestine are highly active in the abdominal cavity. After falling into the RP, they are close to the bank of SV, hindering accurate positioning diagnosis through imaging examinations.

Overall, when a tumor is found in the SV region, in addition to the possibility of it being an SVT, due consideration should also be given to other possibilities like a tumor arising from the bladder, the prostate, the rectum, as well as the small intestine (e.g., a GIST in the small intestine).

The authors declare no conflict of interest.

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