Carpal Tunnel Syndrome Caused by a Juxta-articular Myxoma: A Case Report.

Juxta-articular myxoma (JAM) is a rare soft tissue tumour predominantly composed of mucinous tissue and usually found around large joints. We report a 73-year-old woman with a 5-year history of a soft tissue mass in the thenar eminence of the right wrist who presented to our department. An initial diagnosis of a ganglion cyst was made using magnetic resonance imaging (MRI) and the jellied content of the mass by aspiration. Two years after presentation, surgical treatment with tumour resection and carpal tunnel release via the radial approach was performed because the symptoms of carpal tunnel syndrome worsened, and the tumour invaded the carpal tunnel. Histopathological examination revealed a JAM. At the 1-year follow-up, the symptoms of carpal tunnel syndrome had resolved, and no recurrence was confirmed by MRI. Level of Evidence: Level V (Therapeutic).

Machine-Learning-Based Classification Model to Address Diagnostic Challenges in Transbronchial Lung Biopsy.

BACKGROUND: When obtaining specimens from pulmonary nodules in TBLB, distinguishing between benign samples and mis-sampling from a tumor presents a challenge. Our objective is to develop a machine-learning-based classifier for TBLB specimens. METHODS: Three pathologists assessed six pathological findings, including interface bronchitis/bronchiolitis (IB/B), plasma cell infiltration (PLC), eosinophil infiltration (Eo), lymphoid aggregation (Ly), fibroelastosis (FE), and organizing pneumonia (OP), as potential histologic markers to distinguish between benign and malignant conditions. A total of 251 TBLB cases with defined benign and malignant outcomes based on clinical follow-up were collected and a gradient-boosted decision-tree-based machine learning model (XGBoost) was trained and tested on randomly split training and test sets. RESULTS: Five pathological changes showed independent, mild-to-moderate associations (AUC ranging from 0.58 to 0.75) with benign conditions, with IB/B being the strongest predictor. On the other hand, FE emerged to be the sole indicator of malignant conditions with a mild association (AUC = 0.66). Our model was trained on 200 cases and tested on 51 cases, achieving an AUC of 0.78 for the binary classification of benign vs. malignant on the test set. CONCLUSION: The machine-learning model developed has the potential to distinguish between benign and malignant conditions in TBLB samples excluding the presence or absence of tumor cells, thereby improving diagnostic accuracy and reducing the burden of repeated sampling procedures for patients.

Identification of TEKTIN1-expressing multiciliated cells during spontaneous differentiation of non-human primate embryonic stem cells.

Tektins are a group of microtubule-stabilizing proteins necessary for cilia and flagella assembly. TEKTIN1 (TEKT1) is used as a sperm marker for monitoring germ cell differentiation in embryonic stem (ES) and induced pluripotent stem (iPS) cells. Although upregulation of TEKT1 has been reported during spontaneous differentiation of ES and iPS cells, it is unclear which cells express TEKT1. To identify TEKT1-expressing cells, we established an ES cell line derived from cynomolgus monkeys (Macaca fascicularis), which expresses Venus controlled by the TEKT1 promoter. Venus expression was detected at 5 weeks of differentiation on the surface of the embryoid body (EB), and it gradually increased with the concomitant formation of a leash-like structure at the EB periphery. Motile cilia were observed on the surface of the Venus-positive leash-like structure after 8 weeks of differentiation. The expression of cilia markers as well as TEKT1-5 and 9 + 2 microtubule structures, which are characteristic of motile cilia, were detected in Venus-positive cells. These results demonstrated that TEKT1-expressing cells are multiciliated epithelial-like cells that form a leash-like structure during the spontaneous differentiation of ES and iPS cells. These findings will provide a new research strategy for studying cilia biology, including ciliogenesis and ciliopathies.

Synchronous gastric cancer and primary lymphoma of right adrenal gland: a case report.

This report presents an extremely rare case of synchronous gastric cancer and primary adrenal diffuse large B-cell lymphoma (DLBCL). An 82-year-old man underwent computed tomography, which revealed a heterogeneous appearing and hypodense adrenal mass and a gastric mass with no enlarged lymph nodes in the neck, mediastinum, abdomen, and inguinal region. Upper gastrointestinal endoscopy revealed a protruding gastric tumor. The specimens obtained from endoscopic biopsy were histologically confirmed to be adenocarcinoma. The hormonal findings eliminated functional adrenal tumor. The patient underwent distal gastrectomy with regional lymph node resection for gastric cancer and incisional biopsy of the adrenal mass. Based on the pathological findings, diagnoses of mixed mucinous and tubular adenocarcinomas of the stomach and adrenal DLBCL were confirmed. Postoperation, the patient received rituximab combined with low-dose doxorubicin, cyclophosphamide, vincristine, and prednisone (R-miniCHOP). Six courses of R-miniCHOP were planned, but were completed in only one course at the patient's request. The patient died 2 months after surgery.

Postoperative solitary liver metastasis from esophageal squamous cell carcinoma achieving a clinical complete response to chemotherapy with cisplatin and 5-fluorouracil followed by stereotactic body radiotherapy: A case report.

Treatment strategies for distant organ metastasis have changed markedly since the concept of oligometastasis was introduced. The perception that distant organ metastasis is a systemic disease and not eligible for local therapy is now a thing of the past. Therefore, the present report details a case of postoperative solitary liver metastasis from esophageal squamous cell carcinoma (ESCC), which achieved a clinical complete response to chemotherapy with cisplatin and 5-fluorouracil (5-FU) followed by stereotactic body radiotherapy (SBRT). A 76-year-old male patient underwent esophagectomy for lower thoracic ESCC. At 7 months after surgery, abdominal CT revealed a solitary hypovascular mass, 28 mm in size, in segment 7 of the liver. After three courses of chemotherapy with cisplatin and 5-FU, abdominal CT revealed that the liver mass had shrunk to 7 mm in size. SBRT was then administered with a 6 MV X-ray beam generated by a linear accelerator. A total dose of 50 Gy was given in 5 fractions of 10 Gy to the liver mass. At 1 month after SBRT, abdominal CT revealed that the liver mass had disappeared. The patient received no further adjuvant chemotherapy and had no recurrence at 18 months after diagnosis of liver metastasis and 13 months after SBRT.

Successful resection of a neuroendocrine tumor in the gallbladder: a case report.

BACKGROUND: Gallbladder neuroendocrine tumors (GB-NETs) are extremely rare, representing only 0.5% of all NETs because no neuroectodermal cells are present in the gallbladder. In 2019, the World Health Organization updated the classification of NETs based on their molecular differences. The mutation status of DAXX and ATRX has been added to the criteria for well-differentiated NETs. CASE PRESENTATION: A 50-year-old man presented to our hospital for further examination of a gallbladder polyp. He had no right quadrant pain, fever, jaundice, weight loss, or carcinoid syndrome-related symptoms. The patient hoped to avoid cholecystectomy. During the 3-year observation period, the polyp gradually increased in size from 8.3 to 9.9 mm. He decided to undergo surgery, and whole cholecystectomy was successfully performed. Immunohistochemical staining revealed positivity for chromogranin A, synaptophysin, and CD56. The Ki-67 index was < 3%. Taken together, these results led to a diagnosis of a grade 1 GB-NET. We also performed immunohistochemical staining of DAXX and ATRX, which revealed that DAXX protein expression was negative. The patient's postoperative course was uneventful, and he developed no recurrence for 8 years after surgery. CONCLUSION: We experienced a very rare case of GB-NET. Obtaining a correct preoperative diagnosis is quite difficult at the first evaluation. A GB-NET should be considered as a differential diagnosis of gallbladder tumors.

Occult follicular lymphoma in a swollen regional lymph node of gastric schwannoma.

BACKGROUND: Regional lymphadenopathy is more commonly noted in gastric schwannomas than in other gastric submucosal tumors. Most of the swollen lymph nodes associated with gastric schwannomas are non-metastatic lymphadenopathy. CASE PRESENTATION: A 69-year-old Japanese woman was referred to our hospital with a chief complaint of abdominal discomfort. Contrast-enhanced computed tomography (CT) of the abdomen revealed an extraluminal tumor with heterogeneous enhancement at the middle stomach on the lesser curve, accompanied with one swollen lymph node approximately 10 mm in size and several small lymph nodes in the perigastric region. These lymph nodes were flat; therefore, we considered them to be non-metastatic. The main tumor was removed via wedge resection. Soft and slightly swollen lymph nodes, which were compatible with the lymph nodes noted in the preoperative CT, were found near the main tumor in the fatty tissue at the lesser curvature of the stomach. An excisional biopsy of the largest lymph node was performed for the diagnosis. Based on pathological findings, a diagnosis of gastric schwannoma and follicular lymphoma (FL) was confirmed. The patient is doing well without recurrence of either the gastric schwannoma or FL 28 months postsurgery. CONCLUSIONS: The present report detailed an extremely rare case of FL coincidentally discovered in the swollen regional lymph node of gastric schwannoma.

A Case of Pathological Complete Response Following FOLFIRINOX Therapy for Pancreatic Adenocarcinoma with Synchronous Distant Lymph Node Metastases.

INTRODUCTION: We report a case of conversion surgery for pancreatic ductal adenocarcinoma (PDAC) with synchronous distant metastases showing pathological complete response (pCR) after FOLFIRINOX therapy. PRESENTATION OF CASE: A 46-year-old woman with obstructive jaundice was referred to our hospital. A CT scan revealed a hypo-vascular mass in the head of the pancreas with multiple para-aortic lymph nodes and a Virchow's node swollen. The serum CA 19-9 level was 71795.1 U/mL. The result of tumor biopsy from the biliary stenotic site was concordant with adenocarcinoma. She was diagnosed with PDAC with distant metastases. After 10 courses of FOLFIRINOX followed by 4 courses of FOLFIRI, a CT scan showed that distant lymph node swellings disappeared, and CA19-9 level became almost normal. She underwent pancreaticoduodenectomy with dissection of para-aortic lymph nodes 8 months after the initiation of chemotherapy. Pathologically, no evidence of residual adenocarcinoma was observed in neither pancreas nor lymph nodes. Adjuvant chemotherapy using S-1 was administered for 6 months, and no recurrence has been observed 4 years after surgery. BRCA1/2 mutations were not detected in patient's DNA. DISCUSSION: With the induction of intensive chemotherapies such as FOLFIRINOX, an increasing number of patients with synchronous distant metastases could become suitable candidates for surgery of the primary lesion because of the potential complete response of metastatic lesions. CONCLUSION: This case presented a rare occurrence of pCR in a patient with unresectable PDAC with distant metastases who received FOLFIRINOX. The feasibility and benefits of conversion surgery in such patients must be investigated in future trials.

[Right Hemicolectomy and Pancreatoduodenectomy for Transverse Colon Cancer Invasion to the Duodenum-A Case Report].

A 74-year-old woman visited her local doctor with stomach ache and weight loss. Abdominal ultrasonography showed a mass in the hepatic flexure of the transverse colon. She was referred to our hospital. Colonoscopy revealed transverse colon cancer in the hepatic flexure. Upper endoscopy showed redness of the mucosa and stenosis in the descending portion of the duodenum. Therefore, duodenal invasion was suspected. The CT scan showed a regional lymph node metastasis, but there were no obvious signs of distant metastases. From the aforementioned findings, we diagnosed the patient with duodenal invasion of transverse colon cancer(cT4b, N1, M0, cStage Ⅲ). There was no intraoperative peritoneal dissemination or liver metastasis, and we performed right hemicolectomy and pancreatoduodenectomy for transverse colon cancer. On histopathological examination, we diagnosed pT4b(Duo, Pan), N1b(3/35), M0, pStage Ⅲb. The patient had delayed gastric emptying after surgery. She recovered conservatively and was discharged on POD 37. She underwent adjuvant chemotherapy( capecitabine therapy)and has been alive without recurrence 8 months after surgery. In some cases of colon cancer invasion of other organs, long-term survival can be achieved if R0 resection is possible, and we should consider extended resection.

[A Resected Case of Angiomyolipoma Difficult to Be Distinguished from Hepatocellular Carcinoma].

A 42-year-old man complaining of left back pain was admitted to our hospital. The hepatis B and C surface antigens were negative. The serum levels of tumor markers were within the reference ranges. Abdominal ultrasound revealed an 8 cm-sized, primarily round and hyperechoic mass in the left lateral segment. Contrast-echo showed non-uniform enhancement in the arterial phase and uniform enhancement in the portal phase. This mass did not indicate"wash-out"on contrast- enhanced CT. It showed hypointensity in the hepatobiliary phase on MRI. The definitive diagnosis could not be obtained, and the patient was suspected with malignancy, such as hepatocellular carcinoma(HCC). Therefore, left hemi-hepatectomy was performed for the diagnostic treatment. Based on the immunochemical staining results, he was diagnosed with angiomyolipoma( AML). AML is composed of fat, blood vessels, and smooth muscles. It is regarded as a tumor of perivascular epithelioid cell tumor(PEComa). Early venous return and adipose tissues in the tumor were the distinctive features of this tumor. The preoperative diagnosis of AML without any fatty component as in this case is very difficult.

[A Case of Resected Peritoneal Metastasis from Hepatocellular Carcinoma after Surgery].

A 69-year-old woman with a hepatocellular carcinoma(HCC)was followed-up for type B chronic hepatitis and underwent partial hepatectomy(S6)at our hospital. Afterwards, she underwent radiofrequency ablation(RFA)therapy twice because of intrahepatic recurrence. Seven months after the first hepatectomy, a left adrenalectomy was performed for a left adrenal metastasis. Seventeen months after the first hepatectomy, a splenectomy was performed for a splenic metastasis. Forty-three months after the first hepatectomy, a second hepatectomy was performed for intrahepatic recurrence, and a right adrenalectomy was performed for an adrenal metastasis. Sixty-eight months after the first hepatectomy, an abdominal CT revealed a growing solitary lesion in the ascending colon, which was diagnosed as a peritoneal metastasis. The peritoneal dissemination was removed because there were no other extrahepatic or intrahepatic recurrences. Histologically, the resected specimen was diagnosed as a peritoneal metastasis from a HCC. The patient survived, and there were no recurrences for 6 months after the operation. We report this case of a peritoneal metastasis from a HCC after surgery with a review of the literature.

Solid pseudopapillary neoplasm of the pancreas showing marked distal atrophy: A case report.

INTRODUCTION: Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare neoplasm, affecting primarily young females. Because SPNs are of low-malignancy, they rarely obstruct the main pancreatic duct (MPD) and cause atrophy of the distal pancreas even if their tumor sizes are large. PRESENTATION OF CASE: A 35-year-old female was referred to our hospital due to pancreatic tumor. Imaging findings showed the presence of well-defined round tumor in the body of the pancreas with 25-mm in diameter. The pancreas parenchyma distal to the tumor was markedly atrophic, and MPD dilatation was not observed. The lesion was diagnosed as SPN by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA), and central pancreatectomy was performed. Intraoperative frozen section of the distal atrophic pancreas showed no evidence of acinar cells, indicating exocrine dysfunction. Therefore, we closed distal pancreas stump instead of reconstruction. In the distal atrophic parenchyma, scattered foci of islets of Langerhans and the vestige of dilated MPD were observed. She has shown neither endocrine nor exocrine insufficiency after surgery. DISCUSSION: SPNs are usually found without atrophic change of distal pancreas. To the best of our knowledge, this is the first report of SPN in which exocrine dysfunction of atrophic pancreas was demonstrated pathologically and central pancreatectomy without anastomosis of distal pancreas was chosen for the surgical treatment. CONCLUSION: We reported a very rare case of SPN with marked distal parenchymal atrophy. We successfully performed central pancreatectomy without reconstruction.

Use of ALK Immunohistochemistry for Optimal Therapeutic Strategy of Pulmonary Large-cell Neuroendocrine Carcinoma and Identification of a Novel KIF5B-ALK Fusion Oncokinase.

BACKGROUND: Patients with adenocarcinoma of the lung are routinely screened for anaplastic lymphoma kinase (ALK) rearrangement because they can be treated by ALK-specific targeted therapy. The clinical and molecular characteristics of large-cell neuroendocrine carcinoma (LCNEC) associated with ALK rearrangement are still unclear. Herein, we assessed the ALK status in a series of patients with LCNEC by testing methods commonly used for adenocarcinoma. MATERIALS AND METHODS: ALK expression was first examined by immunohistochemistry. For a positively stained tumor, molecular analyses were then conducted. The ALK fusion partner found in a patient with ALK rearrangement was further identified by direct DNA sequencing. Patient clinicopathological features were also analyzed, focusing on the ALK rearrangement-positive case. RESULTS: Immunohistochemistry of seven patients identified strong ALK expression in one case of stage IV LCNEC. Molecular analysis identified a novel rearranged gene resulting from the fusion of kinesin family member 5B (KIF5B) exon 17 to ALK exon 20. The patient was treated with ALK-specific inhibitors, crizotinib and later, alectinib, and has remained alive for more than 24 months without disease progression. Three of the remaining six patients without ALK rearrangement had stage IV cancer and received cytotoxic chemotherapies. Their average overall survival was 5.4 months. CONCLUSION: To our knowledge, this is the first report of a KIF5B-ALK fusion gene in LCNEC. The patient was successfully treated with ALK inhibitors, suggesting that sensitivity to ALK inhibitor may define a specific LCNEC subtype. We propose that screening for ALK rearrangement in patients with LCNEC may assist in selecting potential candidates for targeted therapy.

Thymidylate synthase expression in primary colorectal cancer as a predictive marker for the response to 5-fluorouracil- and oxaliplatin-based preoperative chemotherapy for liver metastases.

In patients with colorectal liver metastases (CRLM), predictive markers for response to preoperative chemotherapy are lacking. The aim of the present study was to evaluate the expression of thymidylate synthase (TS) and excision repair cross-complementation group 1 (ERCC1) as predictive markers in CRLM. A total of 24 patients with CRLM were included in this study. Tumor response was evaluated using the tumor regression grade (TRG) and Response Evaluation Criteria in Solid Tumors (RECIST) methods. TS and ERCC1 expression in paired CRLM and primary lesions were assessed by immunohistochemistry. We analyzed correlations between i) the response to preoperative chemotherapy evaluated by TRG and RECIST, ii) TS and ERCC1 expression and the response evaluated by TRG and RESICT, and iii) TS and ERCC1 expression in matched pairs of primary tumor and CRLM. The preoperative chemotherapy response evaluated by TRG and RECIST was significantly associated (P=0.0005). The response based on RECIST criteria and TRG was significantly associated with TS expression in the primary tumor (P=0.0272, and P=0.0137, respectively). No correlations were detected between marker expression in the primary tumor and in CRLM for either TS or ERCC1 (P=0.371 and P=1.00, respectively). Our data suggested that TS expression in the primary tumor is a predictive marker of preoperative chemotherapy response in CRLM based on both TRG and RECIST methods.

Epithelioid sarcoma in the chest wall: a case report and literature review.

BACKGROUND: Epithelioid sarcoma (ES) is a rare variant of soft tissue sarcoma. The proximal type of ES occurs in various locations. We present a resected case with proximal-type ES that occurred in the chest wall and discuss the relevant literature. CASE PRESENTATION: A 47-year-old woman was referred for a 6-month history of a right anterior chest mass with tenderness. Chest computed tomography showed an invasive chest wall mass with calcification surrounding the third rib. Aspiration biopsy cytology suggested malignancy. We performed wide resection, including the middle part of the pectoralis major muscle, the pectoralis minor muscle, the third and fourth ribs, and reconstruction of the chest wall, using a 2-mm polytetrafluoroethylene patch. Severe deformation of the chest wall was avoided. Postoperative physical therapy of the shoulder was effective for the continuous pain and weakness of the arm. She has remained alive for 1 year and 10 months without recurrence. Our literature review showed five previously reported cases of ES in the chest wall, and all of these were surgically resected. Two of these patients suffered from frequent local recurrence and died of disease. CONCLUSIONS: ES in the chest wall is rare. Previous reports have indicated that surgical resection with tumor-free margins is essential for treatment. We performed complete resection of the tumor in our case, and a polytetrafluoroethylene patch was effective for reconstructing the deficit in the chest wall.

Regrowth and progression of multiple calcifying pseudoneoplasms of the neuraxis: Case report.

BACKGROUND: Calcifying pseudoneoplasms of the neuraxis (CAPNONs) are clinically rare, nonneoplastic, noninflammatory-calcified lesions of the central nervous system. Resection of a lesion usually indicates good prognosis without recurrence. However, we experienced a unique case of CAPNON that repeatedly recurred after resection. CASE DESCRIPTION: A 52-year-old woman with recurrence of an undiagnosed brain tumor, which was resected 12 years ago, was admitted to our institution. Three calcifying lesions along with perifocal edema were detected in the frontal interhemispheric fissure. We performed the second surgery for total removal of the lesions. The patient was diagnosed with CAPNON on the basis of the clinical features of the lesions and medical examination results. However, 14 months after the second surgery, recurrence occurred, and the patient has been followed up conservatively thereafter. CONCLUSION: CAPNONs may indicate healing process associated with an unidentified agent. Maximum resection, including an unidentified agent, is necessary to prevent recurrence.

Collision tumor of choriocarcinoma and small cell carcinoma of the stomach: A case report.

INTRODUCTION: Both gastric choriocarcinoma and small cell carcinoma are extremely rare, both accounting for approximately 0.1% of all gastric cancers. Therefore, simultaneous occurrence of gastric choriocarcinoma and small cell carcinoma is even rarer. PRESENTATION OF CASE: An 84-year-old Japanese man was referred to our hospital with the chief complaint of dysphagia. Laboratory data showed iron deficiency anemia. Contrast-enhanced computed tomography of the abdomen revealed thickened wall of the stomach at the fundus and several enlarged abdominal lymph nodes. Upper gastrointestinal endoscopy showed a friable gastric tumor with necrosis in the gastric cardia extending to the abdominal esophagus. Small cell carcinoma was diagnosed based on pathological examination of biopsy specimens. The anemia, which was probably because of tumor bleeding, progressed despite repeated transfusion; therefore, a semi-urgent laparotomy was performed to control hemorrhage. Finally, total gastrectomy and lymph node resection were performed. Based on pathological findings, a diagnosis of collision tumor of choriocarcinoma and small cell carcinoma of the stomach was confirmed. DISCUSSION: When encountering large tumors with necrosis or hemorrhage in the stomach, the possibility of choriocarcinoma component should be considered. Moreover, when small cell carcinoma is morphologically suspected, even if slightly, additional immunohistochemical staining must be performed. CONCLUSION: This report detailed an extremely rare case of collision tumor of choriocarcinoma and small cell carcinoma of the stomach.

Disseminated carcinomatosis of the bone marrow with disseminated intravascular coagulation as the first symptom of recurrent rectal cancer successfully treated with chemotherapy: A case report and review of the literature.

Disseminated carcinomatosis of the bone marrow (DCBM) is a condition in which bone marrow (BM) metastases diffusely invade the BM, and is frequently accompanied by disseminated intravascular coagulation (DIC). While prostate, lung, breast and stomach malignancies, in addition to neuroblastoma, are the most prevalent non-hematological malignancies to metastasize frequently to the BM, colorectal cancer is a malignancy that rarely metastasizes to the BM. The present case describes a 65-year-old male patient treated by resection and one course adjuvant chemotherapy for stage IIIC rectal cancer who presented with nasal bleeding at 8 months post-surgery. A blood test exhibited DIC. A BM biopsy was performed and the definitive diagnosis was DCBM with DIC. Promptly, anti-DIC treatment and chemotherapy with a modified FOLFOX6 (folinic acid, leucovorin (LV), 5-fluorouracil (5-FU) and oxaplatin) regimen was started. Following 1 cycle of chemotherapy, DIC was improved and subsequent to 2 cycles of modified FOLFOX6 the patient was discharged. The patient was alive 263 days subsequent to the diagnosis of DIC, but succumbed to carcinomatous meningitis as a result of disease progression. To the best of our knowledge, this is the first report of DCBM with DIC of curatively resected rectal cancer as the first presentation of relapse that was successfully treated with aggressive therapy, including chemotherapy.

Small, spontaneously ruptured gastrointestinal stromal tumor in the small intestine causing hemoperitoneum: A case report.

INTRODUCTION: Gastrointestinal stromal tumors (GISTs) are clinically asymptomatic until they reach a significant size; therefore, GISTs that are 2cm or less are typically asymptomatic. Patients with symptomatic GISTs typically present with abdominal pain, gastrointestinal bleeding, or a palpable mass but rarely present with hemoperitoneum. PRESENTATION OF CASE: A 72-year-old Japanese man presented to us with acute onset abdominal pain. Physical examination showed peritoneal irritation in the lower abdomen. Findings of abdominal computed tomography were suggestive of hemoperitoneum; therefore, urgent surgery was performed. Approximately 1500ml of blood in the abdominal cavity was removed. A small, ruptured mass was found in the middle of the small intestine, and partial resection of the small intestine, including the mass, was performed. The resected tumor was 2cm in size and exhibited an exophytic growth pattern. Immunohistochemical staining revealed that the tumor was positive for KIT and CD34; therefore, a final diagnosis of GIST was made. Treatment with imatinib at 400mg per day was started from postoperative month 1. The patient is doing well without recurrence 5 months after surgery. DISCUSSION: Even small GISTs in the small intestine can spontaneously rupture and cause hemoperitoneum. Moreover, when a patient presents with sudden abdominal pain and hemoperitoneum without an evident mass on imaging, clinicians should be aware of the possibility of bleeding from a small GIST in the small intestine. CONCLUSION: We present an extremely rare case of a patient with a small, spontaneously ruptured GIST in the small intestine, resulting in hemoperitoneum.