The most common acute symptoms of GIST are gastrointestinal bleeding, abdominal pain, and ileus. Gastric GIST symptoms depend on tumor location, size, and development form . Gastrointestinal bleeding is caused by tumor growth, necrosis, and exposure to ulcers in the lumen, whereas abdominal pain is caused by tumor perforation and intraabdominal bleeding. The cause of ileus is thought to be tumor compression rather than luminal obstruction. As GISTs grow externally, there is a risk of obstruction caused by GIST-induced gastric volvulus, but it has rarely been reported in practice. To the best of knowledge, this is probably the first report of gastric volvulus during imatinib administration.
In patients with gastric volvulus, the stomach is either insufficiently fixed and/or physiologically involves some torsional mechanisms, resulting in gastric rotation. Gastric volvulus is divided into two types: organoaxial volvulus (long-axis volvulus) centered along the axis connecting the cardia and pylorus, and mesenteroaxial volvulus (short-axis volvulus) centered along the axis of the greater and lesser curvature. There is also a mixed volvulus type in which both types coexist; its causes are idiopathic or secondary, depending on the pathogenesis. Idiopathic causes include laxity of the four ligaments that hold the stomach in place and gastric ptosis, whereas secondary causes include esophageal hernia, diaphragmatic hernia, and tumors. In the idiopathic type, the stomach sometimes twists more than 360°, which may lead to hemorrhage, perforation, and necrosis due to disturbed blood flow. A surgical delay can result in progression to devastating morbidities, including gastric ischemia. Therefore, it is important to identify the disease for early diagnosis. Borchardt’s triad of symptoms, including severe epigastric distension, retching, and inability to pass a nasogastric tube, are considered typical symptoms . However, symptoms vary depending on the type and degree of torsion. In our case, although abdominal pain and retching were mild, it was difficult to differentiate them from the side effects of imatinib administration or the accompanying symptoms of the tumor. However, differential diagnosis should be suspected based on clinical symptoms because imaging studies show characteristic findings. CT can show dilatation of the gastric lumen and fluid retention, and gastric volvulus can be easily diagnosed, especially if the images are reconstructed using 3D-CT.
According to Velasco et al. , 85% of gastric GISTs involve a extragastric mass and 7% grew exophytically. Therefore, a relatively large GIST may develop extramurally, and its weight may cause traction and twisting of the intestine. Then, the tumor location is important; in the case of organoaxial volvulus, the tumor must be located on the lesser curvature side. To date, there are two case reports of GIST-induced gastric volvulus, one of which was an upside-down stomach due to a hiatal hernia with GIST . Upside-down stomach is an idiopathic form of organoaxial volvulus associated with a high degree of esophageal hiatal hernia, wherein the stomach prolapses into the mediastinum. This condition is one of the major forms classified by Bettex et al. . The other case was of a GIST with extramural growth in the gastric lesser curvature, resulting in an organoaxial volvulus, as in the present case . In this report, the GIST was 9 cm in diameter and weighed 224 g, which is a large and heavy tumor, as in the present case, suggesting that tumor localization, diameter, and weight are important factors for tortuosity. In our case, the GIST was initially very large and was suspected to be adherent to the surrounding organs; therefore, the GIST was immobile and did not twist. However, as the GIST shrank with imatinib treatment, the GIST became mobile and volvulous. Therefore, if a giant GIST is located externally on the lesser curvature of the gastric wall and neoadjuvant imatinib is administered for its treatment, gastric volvulus may occur once the tumor shrinks and mobility is achieved.
Gastric volvulus may be treated by decompression using a nasogastric tube or it may be corrected endoscopically in the case of the mesenteric-axial type, which has no closure of the cardiac orifice . However, this approach is only for symptomatic management, and surgical treatment, including tumor resection, is necessary when traction and torsion are caused by a tumor . Furthermore, surgical resection is the most effective treatment for GISTs in the absence of noncurative factors. In our case, neoadjuvant imatinib was administered to avoid complicated resection owing to the large tumor size and suspected adhesion and invasion of the surrounding organs.
Neoadjuvant imatinib for giant gastric GIST has not been established, but it is expected to shrink the tumor, prevent tumor rupture, and preserve stomach function by avoiding total gastrectomy. Kurokawa et al.  reported a phase II study of neoadjuvant imatinib treatment for giant gastric GISTs. The R0 resection rate without tumor rupture was 91%, and only 6% of patients required total gastrectomy. The response to imatinib treatment can be predicted during the treatment course using genetic typing . However, if genetic analysis is not performed or kit mutations cannot be detected, imaging examinations should be performed after the first month of imatinib treatment. In particular, early evaluation using PET-CT is recommended to assess treatment response in patients treated with neoadjuvant imatinib . Evaluating metabolic changes rather than morphological changes is more reliable . FDG-PET/CT metabolic studies 8 weeks after initiating imatinib therapy may be useful for assessing early therapeutic effects . Furthermore, > 50% reduction in standardized uptake values (SUVs) and/or an SUV of < 2.5 in the follow-up study may be a more robust criterion for the assessment of a sustained response . In our case, at the first assessment after initiating imatinib treatment, the tumor did not shrink but the SUV was < 2.0. After 18 months of continued imatinib treatment, the GIST shrank and unexpectedly developed gastric volvulus; however, R0 resection was achieved. The expected time for performing resection after neoadjuvant imatinib treatment was 36–48 weeks  ; therefore, surgery should be performed once mobility is achieved and deemed possible after an earlier evaluation.
In conclusion, gastric volvulus caused by GIST is rare, but should remain part of the differential diagnosis in patients presenting with abdominal pain and retching. It should be noted that a giant GIST, especially in the lesser curvature of the stomach, may twist the stomach and cause gastric volvulus.