Gastric smooth muscle tumors may either be leiomyomas or gastrointestinal stromal tumors. The gastrointestinal stromal tumors are characterized by their larger size (usually >1 cm), by the number of mitoses, and by the presence of a C-Kit mutation on exon 9 or 11. Although the differentiation between leiomyoma and gastrointestinal stromal tumor (GIST) is a relatively new distinction, it has some importance from a surgical perspective, as GISTs have a greater propensity for recurrence and must be resected with a margin of normal stomach circumferentially. On the other hand, leiomyomas, which are most common in the esophagus, can also be found in the proximal stomach. These can be treated with either wedge resection or an endogastric “shelling out” when they are small and symptomatic (see Chapter 38). Asymptomatic lesions less than 1 cm can generally be observed.
The minimally invasive resection of GISTs requires good clinical judgment. Although there is no specific size of GIST that defines the need for an open (vs. laparoscopic) resection, most surgeons use 6 cm in the largest dimension of the tumor as the upper limit of safety for minimally invasive resection. As the tumors get larger, the need for a large counterincision to remove the tumor intact negates much of the benefit of the laparoscopic approach. Larger tumors pose a greater risk for local and regional recurrence, making the laparoscopic approach less appealing.
GISTs may occur anywhere in the stomach, but are more common proximally. In order to safely remove a GIST with a wide local resection, the surgeon must have excellent access to the tumor and the normal surrounding stomach. Particularly difficult places to remove these tumors are in the region of the gastroesophageal junction, on the high posterior wall of the stomach, and on the lesser curvature of the stomach. Thankfully, most such tumors are located in a more favorable position closer to the greater curvature. Pre-pyloric GISTs are rare but are probably best addressed with a sleeve resection of the antrum with hand-sewn or stapled laparoscopic B1 reconstruction.
Before addressing the gastric smooth muscle tumor, several imaging studies are necessary. The primary imaging test necessary is esophagogastroduodenoscopy (EGD) to determine the exact location of the lesion in the stomach, and to demonstrate that the lesion is submucosal and not a mucosa-based lesion such as gastric cancer. The next study should be an upper abdominal computed tomography (CT) scan to define the intra- and extragastric components of the tumor as well as to determine whether the tumor is localized or not. With disseminated disease, resection of the primary tumor is not indicated unless it is actively bleeding or obstructing the stomach. Last, endoscopic ultrasound with fine-needle aspiration may be obtained to prove that the tumor harbors spindle cells and to determine, through specialized stains, if the lesion is a GIST or leiomyoma.