Multiple small intestinal stromal tumours in a patient with previously unrecognised neurofibromatosis type 1: immunohistochemical and ultrastructural evaluation

Isolated colonic neurofibroma, a rare tumor: A case report and review of literature

BACKGROUND

Neurofibromas are tumors comprised of peripheral nerve sheath and connective tissue components. They can occur sporadically or as part of familial syndromes such as neurofibromatosis type 1. Isolated colonic neurofibroma without systemic manifestations is a rarely reported clinical entity. Here we present a case of a 51 years old male with an isolated colonic neurofibroma seen on a screening colonoscopy.

CASE SUMMARY

Fifty-one years old male who was otherwise healthy without a significant family history of cancer underwent a screening colonoscopy and was found have a 2.3 cm × 1.4 cm lesion in the colon. Tissue biopsy revealed a spindle cell tumor. Magnetic resonance imaging of the pelvis was negative for adenopathy. He underwent an endoscopic ultrasound that showed an ill-defined avascular lesion of mixed echogenicity measuring 2.8 cm × 15.2 cm in the submucosa with no communication with muscularis mucosa or propria. Immunohistochemistry staining of the tumor was strongly positive for S100, with rare penetrating axons deep within the tumor. Tumor cells were negative for c-kit and desmin and had low Ki-67 index. These findings were consistent with a solitary colonic submucosal neurofibroma. A detailed history and physical examination did not reveal any evidence of extraintestinal neurofibromatosis. He underwent transanal surgical resection of the tumor. The patient tolerated the procedure well without any complications.

CONCLUSION

While neurofibromas have been well described in literature, an isolated colonic neurofibroma is a rare pathological entity. Malignant transformation of neurofibromas has been reported in patients with neurofibromatosis syndromes. We report a case of isolated colonic neurofibroma and highlight the importance of resection due to the increased risk of tumorigenesis.

Neurofibroma discharged from the anus with stool: A case report and review of literature

Isolated neurofibromas that affect the gastrointestinal tract are rare and almost always manifest as neurofibromatosis type 1 or multiple endocrine neoplasia type 2b. In this paper, we present a case of a 24-year-old female with abdominal pain who discharged a neurofibroma in her stool without any blood on it. A colonoscopy showed multiple small polyps in the sigmoid colon and a nodule in the ileocecus. The pathology results and the immunohistochemical stains of the removed neoplasm from the ileocecus confirmed the diagnosis was a bowel neurofibroma. We report a rare case of ileocecal neurofibroma due to the patient’s affected gastrointestinal tract, without any associated systemic syndrome other than a neurofibroma discharged in the stool.

Gastrointestinal Stromal Tumors (GISTs): From Science to Targeted Therapy

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. GISTs represent a distinct category of tumors characterized by oncogenic mutations of the KIT receptor tyrosine kinase in a majority of patients. KIT is useful not only for the diagnosis but also for targeted therapy of this disease. Imatinib, a tyrosine kinase inhibitor, is widely used in advanced and metastatic GISTs. This agent revolutionized the treatment strategy of advanced disease and is being tested in the neoadjuvant and adjuvant settings with encouraging results. New therapeutic agents like sunitinib have now been approved, enriching the treatment scenario for imatinib-resistant GISTs. The present review reports on the peculiar characteristics of this disease through its biology and molecular patterns, focusing on the predictive value of KIT mutations and their correlation with clinical outcome as well as on the activity of and resistance to approved targeted drugs.

An unusual cause of hemoperitoneum: case report with review of literature

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Spontaneous hemoperitoneum (SH) is a rare entity.

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The clinical presentation of isolated neurofibromatous lesions of the intestines are variable.

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In asymptomatic patient no treatment may be required and patient may be kept on follow up.

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Occasionally, they manifest with complications such as intestinal bleeding, obstruction or perforation. Surgery is the treatment of choice in symptomatic intestinal neurofibroma.

Spontaneous hemoperitoneum (SH) is a rare entity which can be life-threatening. Gastrointestinal neurofibromas are rare. Occasionally, such lesions may be the initial sign of NF1 in patients without any other clinical manifestations of the disease. The clinical presentations of isolated neurofibromatous lesions of the intestines are variable. In asymptomatic patient no treatment may be required and patient may be kept on follow up. Occasionally, they manifest with complications such as intestinal bleeding, obstruction or perforation. Surgery is the treatment of choice in symptomatic intestinal neurofibroma. We present the case of a 55 year-old male with acute abdomen due to rupture of isolated neurofibroma as one of the cause of SH. This case represents a rare presentation of isolated intestinal neurofibromatosis in a patient without systemic manifestations and highlights the need for high index of suspicion to exclude neurofibromatosis type 1 or multiple endocrine neoplasia type 2b.

Neurofibromatosis type-1 with retroperitoneal stromal tumour: one case report

BACKGROUND

Neurofibromatosis with gastrointestinal stromal tumours have been reported several times, while neurofibromatosis with retroperitoneal stromal tumours are very rare.

CASE DESCRIPTION

We report the case of a 44-year-old man with a long history of neurofibromatosis. He complained of severe constipation and left leg pain. The patient's examination showed prominent peripheral cutaneous neurofibromas mainly in the belly and limbs, especially a huge mass in his abdomen, no less than ten café-au-lait spots, four Lisch nodules of the iris. Computed tomography and magnetic resonance imaging revealed a round and lobular mass in the retroperitoneal space. It was a well-circumscribed, hypervascular mass with cystic necrosis. A surgical resection was performed, and pathology and immunohistochemistry findings were consistent with stromal tumour. The c-kit gene and platelet-derived growth factor receptor-α gene mutations are not observed in the specimen.

CONCLUSIONS

Neurofibromatosis with retroperitoneal stromal tumour is very rare, and radiological, pathological and immunohistochemical examination may identify it. Surgical resection may be the unique method of cure for it.

Solitary intestinal neurofibroma with no associated systemic syndromes causing intussusception: Case report and literature review

INTRODUCTION

The isolated presence of neurofibromatous lesions in the gastrointestinal tract, with no associated systemic syndromes, is a rarely reported clinical entity.

PRESENTATION OF CASE

A 48-year-old lady, with no history of neurofibromatosis or other systemic disease, presented with small bowel obstruction secondary to an ileo-ileal intussusception induced by an isolated ileal neurofibromatous mass. The patient underwent a segmental enterectomy and after a smooth recovery, she was put on a long-term follow-up schedule.

DISCUSSION

This article presents a review of the literature of this area clinical entity. Very few reports of gastrointestinal isolated neurofibromas could be found. Similarly, extra-digestive isolated lesions have been rarely reported.

CONCLUSION

Isolated ileal neurofibroma is a rare pathological entity. The clinical significance of such a diagnosis lies mainly in the need of further follow up of these patients as the bowel involvement could be the first manifestation of neurofibromatosis type 1 or multiple endocrine neoplasia type 2b.

Gastrointestinal stromal tumor with structures resembling intracytoplasmic lumina

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gut. It is characterized by positive immunostaining for CD117, and bears mutations in the c-kit or PDGFRA genes. Its origin remains uncertain. GISTs mainly possess primitive smooth muscle or neuronal differentiation. Although an epithelioid pattern of GIST is a common finding on light microscopy, true epithelial differentiation has never been demonstrated by either immunohistochemistry or ultrastructural study. Here the authors report an epithelioid GIST of the stomach, immunopositive for CD117, DOG1.1, CD34, and PDGFRA, with slight cytoplasmic staining for epithelial membrane antigen. One heterozygous mutation on codon 842 of exon 18 of the PDGFRA gene was also found. Ultrastructurally, tumor cells had plentiful organelles, including some membrane-bound, dense-core granules and cytoplasmic vacuoles. Intermingled thin cellular processes were also found. Unusually, there were many structures resembling glandular epithelial intracellular lumina with processes. The processes, although resembling microvilli, did not have filament cores, while the lumina were either empty or contained some dense or flocculent content of uncertain nature. True intracellular lumina are very rare in GIST and the authors present findings related to this issue, with a discussion on their nature, origin, and significance.

Surgical Management of Abdominal Manifestations of Type 1 Neurofibromatosis: Experience of a Single Center

Neurofibromatosis type 1 (NF1) is a genetic disease characterized by neoplastic and nonneoplastic disorders involving tissues of neuroectodermal and mesenchymal origin. The mainly involved districts are skin, the central nervous system, and eye and there is a wide range of severity of clinical presentations. Abdominal manifestations of NF1 include five kinds of tumors: neurogenic tumors (neurofibromas, malignant peripheral nerve sheath tumors [MPNSTs], and ganglioneuromas); neuroendocrine tumors (pheochromocytomas and carcinoids); nonneurogenic gastrointestinal stromal tumors (GISTs); embryonal tumors; and miscellaneous. The present experience depends on the participation in the National Project for Diagnosis and Treatment of Rare Diseases. In the group of patients with a diagnosis of von Recklinghausen disease, 10 patients underwent surgical treatment for gastrointestinal and retroperitoneal tumors associated with NF1. Three patients underwent adrenalectomy for pheochromocytoma (in one case associated with jejunal wall neurofibroma); two patients were found to be affected by MPNST (recurrent and unresectable in one case). One patient was affected by giant gastric GIST and jejunal neurofibroma; two patients were affected by extraperitoneal neurofibroma (pararenal and pararectal position); one patient was affected by giant colic neurofibroma and one patient was affected by retroperitoneal bilateral plexiform neurofibromas. Early diagnosis of these abdominal manifestations is very important because of the risk of malignancy, organic complications (such as pheochromocytoma), or hemorrhagic–obstructive complications such as in case of tumors of the gastrointestinal tract (GISTs and neurofibromas). The importance of an annual clinical evaluation on the part of a multidisciplinary pool of clinicians in highly specialized centers allows early detection of complications and of neoplastic transformation. Genetic screening allows preclinical diagnosis with a sensibility of 95 per cent. Further studies are necessary to detect predictive factors of malignant tumor development of severe clinical conditions.

Gastrointestinal and retroperitoneal manifestations of type 1 neurofibromatosis

BACKGROUND

Type 1 neurofibromatosis (NF1) is a genetic disease characterized by neoplastic and not neoplastic disorders, involving tissues of neuroectodermal or mesenchymal origin. The mainly involved districts are skin, central nervous system, and eye, and there is a wide range of severity of clinical presentations.

DATA SOURCES

Abdominal manifestations of NF1 comprehend five categories of tumors: neurogenic with neurofibromas, malignant peripheral nerve sheath tumors and ganglioneuromas, neuroendocrine with pheochromocytomas and carcinoids, non-neurogenic gastrointestinal stromal tumors, i.e., GISTs, and embryonal tumors and miscellaneous.

CONCLUSIONS

Early diagnosis of these abdominal manifestations is very important given the risk of malignancy, organic complications such as in the case of pheochromocytomas or hemorrhagic-obstructive complications such as in the case of the tumors of the gastrointestinal tract (GISTs and neurofibromas). The importance of an annual clinical evaluation on the part of a multidisciplinary pool of clinicians in highly specialized centers allows early detection of complications and of neoplastic transformation.

Isolated intestinal neurofibromatous proliferations in the absence of associated systemic syndromes

Gastrointestinal tract involvement by neurofibromatous lesions is rare and occurs most frequently as one of the systemic manifestations of generalized neurofibromatosis type 1 (NF1). In this setting, the lesions may manifest as focal scattered neurofibromas or as an extensive diffuse neural hyperplasia designated ganglioneuromatosis. Occasionally, such lesions may be the initial sign of NF1 in patients without any other clinical manifestations of the disease. Rarely, cases of isolated neurofibromatosis of the large bowel with no prior or subsequent evidence of generalized neurofibromatosis have been documented. We present the case of a 52 year-old female with abdominal pain and alternating bowel habits. Colonoscopic evaluation revealed multiple small polyps in the cecum and the presence of nodular mucosa in the colon and rectum. Pathologic evaluation of the biopsies from the cecum, descending colon, sigmoid colon, and rectum revealed tangled fascicles of spindle cells expanding the lamina propia leading to separation of the intestinal crypts. Immunohistochemical stains helped confirm the diagnosis of diffuse intestinal neurofibromatosis. A thorough clinical evaluation failed to reveal any stigmata of generalized neurofibromatosis. This case represents a rare presentation of isolated intestinal neurofibromatosis in a patient without classic systemic manifestations of generalized neurofibromatosis and highlights the need in such cases for close clinical follow-up to exclude neurofibromatosis type I or multiple endocrine neoplasia type II.

Aspectos tomográficos do tumor estromal gastrintestinal de origem gástrica: estudo de 14 casos

OBJETIVO: Descrever os achados tomográficos do tumor estromal gastrintestinal de origem gástrica. MATERIAIS E MÉTODOS: No período de janeiro de 1999 a dezembro de 2006, foram selecionados 14 pacientes com diagnóstico histopatológico e imuno-histoquímico de tumor estromal gastrintestinal gástrico que apresentavam tomografia computadorizada realizada anteriormente ao tratamento. As variáveis tomográficas analisadas foram: topografia da lesão, dimensões, homogeneidade, contornos, limites, morfologia, padrão e intensidade do realce pelo meio de contraste venoso, padrão de crescimento, invasão de órgãos adjacentes, presença de ulceração, fístula, calcificações, infiltração da gordura mesentérica, linfonodomegalias e metástases a distância. RESULTADOS: Os tumores foram localizados no corpo (57,1%) ou fundo gástrico (42,9%), com dimensões variando entre 6,0 e 23,0 cm (média de 11,5 cm). O crescimento foi predominantemente extraluminal (57,1%) ou intra/extraluminal (35,7%). O realce pelo contraste venoso foi discreto em 50% dos casos, moderado em 50% e heterogêneo em 64,3%. Foram ainda observadas hipodensidade central em 64,3% dos casos, invasão de órgãos adjacentes em 42,9% e metástases hepáticas em 7,2%. CONCLUSÃO: No presente estudo, a maioria dos tumores localizava-se no corpo gástrico, com tamanho médio de 11,5 cm, apresentando área hipodensa central, realce heterogêneo pelo meio de contraste e crescimento predominantemente extraluminal.

Gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. These form a distinct category of tumors characterized by oncogenic mutations of the KIT receptor tyrosine kinase in a majority of patients. KIT is used not only for diagnosis but also for targeted therapy of GISTs. Imatinib, a tyrosine kinase inhibitor, is widely used in the treatment of advanced and metastatic GISTs and has been recently employed in the neo adjuvant and adjuvant set-up with encouraging results. Certain specific mutations in an exon (such as in exon 9) of the KIT gene result in GISTs that are relatively unresponsive to the Imatinib treatment. New therapeutic agents like Sunitinib have now been approved for the treatment of Imatinib-resistant GIST. This review summarizes the salient features of GIST along with a detailed review of targeted multi-disciplinary approach to the treatment of these special tumors.

Gastrointestinal stromal tumors: diagnostic challenges and practical approach to differential diagnosis

Over the last decade, gastrointestinal stromal tumors (GISTs) have evolved from histogenetically obscure gastrointestinal mesenchymal tumors to well-defined tumors with distinctive clinical, morphologic, ultrastructural, histogenetic, and molecular characteristics, for which targeted therapy is available. This is largely attributable to the discovery of CD117 overexpression and activating mutations in c-kit or platelet-derived growth factor alpha genes in most of GISTs. The availability of specific diagnostic tests and targeted therapy for GISTs has led to an increased awareness of these tumors. At the same time, the list of potential GIST mimics has lengthened considerably and it has become increasingly important that GISTs be distinguished from their mimics because correct diagnosis has implications for both treatment and prognosis. The purpose of this review is to provide an update of the expanding differential diagnosis of GISTS, to draw attention to unusual GIST variants, to provide a practical approach the differential diagnosis of GISTs and to highlight some of the challenges faced by pathologists in resolving this differential diagnosis.

Life-threatening gastrointestinal haemorrhage in Von Recklinghausen's disease

Neurofibromatosis Type I (NF-1), also known as Von Recklinghausen's disease, is a common disorder, but gastrointestinal manifestations are rare and can be associated with severe complications and malignancy. We describe a case of multiple intestinal tumours, which presented as major per-rectal bleeding and was diagnosed by laparotomy. Presenting symptoms of this condition are usually non-specific, but the risk of malignancy and perforation should allow for a high index of suspicion in patients with NF-1 presenting with gastrointestinal symptoms. We present this case as a reminder that blood loss from the bowel in Von Recklinghausen's disease may be life-threatening, requiring immediate surgery to control haemorrhage.

From the archives of the AFIP: abdominal neoplasms in patients with neurofibromatosis type 1: radiologic-pathologic correlation

Neurofibromatosis type 1 (NF1) is one of the most common genetic disorders. NF1 is a complex disease resulting from a spectrum of mutations that may occur at many locations along the large, complex NF1 gene, which is located on chromosome 17. Mutations of the NF1 gene lead to abnormal tumor suppression. Consequently, patients with NF1 have an increased prevalence of benign and malignant neoplasms throughout the body. There are five categories of NF1 tumors that occur in the abdomen: neurogenic, neuroendocrine, nonneurogenic gastrointestinal mesenchymal, embryonal, and miscellaneous. Many of these tumors are age related, occur at specific anatomic locations, and have unique imaging features. Notably, many patients have a variety of organs affected because there is a high prevalence of multiple tumors occurring in the same patient. Neurofibromas are the most common benign neoplasms and may occur in the retroperitoneum or visceral organs. Malignant peripheral nerve sheath tumor is an aggressive malignancy that is the most common malignant tumor of the abdomen in patients with NF1. Interpreting abdominal imaging studies in patients with NF1 can be challenging because of the wide spectrum and diverse nature of tumors that occur in this disease.

Gastrointestinal stromal tumors in patients with neurofibromatosis 1: a clinicopathologic and molecular genetic study of 45 cases

Gastrointestinal stromal tumors (GISTs), the specific KIT- or PDFGRA-signaling driven mesenchymal tumors, most commonly occur sporadically, but there seems to be some increased tendency for these tumors to develop in patients with neurofibromatosis 1 (NF1). The clinicopathologic profile, KIT, and PDGFRA mutation status and long-term prognosis of patients with GIST in NF1 are incompletely characterized. In this study, we analyzed 45 patients who had NF1 and GIST. There were 26 females and 19 males with a median age of 49 years (10 years lower than the median age of GIST patients in general). A great majority of tumors occurred in the jejunum or ileum, with multiple tumors occurring in 28 cases. Ten patients had a duodenal and one had a gastric GIST. The most common presentations were gastrointestinal bleeding and anemia, and many patients had intermittent bleeding over several years. The majority of the tumors were small and mitotically inactive; only 7 had mitotic activity >5/50 HPFs and 15 tumors were >5 cm. Associated Cajal cell hyperplasia was common. One patient had an intraabdominal peri-intestinal neurofibroma. Five of 35 patients with follow-up died of metastatic disease; all of these had a tumor >5 cm, mitotic rate >5/50 HPFs, or both; three of these tumors were located in the duodenum. The presence of multiple small tumors was not associated with progressive disease. Most patients with long-term follow-up enjoyed a good prognosis; 2 died of other NF1-associated tumors (malignant peripheral nerve sheath tumors, brain tumor). None of the 16 tumors from 15 patients had a KIT exon 9, 11, 13, or 17 or PDGFRA exon 12 or 18 mutation as is typically seen in sporadic GISTs, indicating that GISTs in NF1 patients have a different pathogenesis than sporadic GISTs.

A case of a gastrointestinal stromal tumour presenting as acute abdomen

BACKGROUND

Gastrointestinal stromal tumour (GIST) has many modes of presentation. This is the first reported GIST presenting as an acute abdomen.

METHODS

A man presented with signs and symptoms suggestive of acute appendicitis. Examination under anaesthesia revealed a mass. At laparotomy a strangulated mass was found originating from the greater curve of the stomach. Subsequent histopathology confirmed this to be a gastrointestinal stromal tumour, probably of a benign nature. Post-operative investigations did not show any metastatic spread.

CONCLUSIONS

GISTs arise from the gastrointestinal tract, omentum, and mesentery. Presentation is generally non-specific and it is rare for them to present acutely. Management should include staging to exclude any metastatic spread.

Multiple gastrointestinal stromal tumors in type I neurofibromatosis: a pathologic and molecular study

Multiple gastrointestinal stromal tumors typically occur in familial form associated with KIT receptor tyrosine kinase or platelet-derived growth factor receptor-alpha (PDGFRA) germline mutations, but may also develop in the setting of type 1 neurofibromatosis. The molecular abnormalities of gastrointestinal stromal tumors arising in neurofibromatosis have not been extensively studied. We identified three patients with type 1 neuro-fibromatosis and multiple small intestinal stromal tumors. Immunostains for CD117, CD34, desmin, actins, S-100 protein, and keratins were performed on all of the tumors. DNA was extracted from representative paraffin blocks from separate tumor nodules in each case and subjected to a nested polymerase chain reaction, using primers for KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18, followed by direct sequencing. The mean patient age was 56 years (range: 37-86 years, male/female ratio: 2/1). One patient had three tumors, one had five, and one had greater than 10 tumor nodules, all of which demonstrated histologic features characteristic of gastrointestinal stromal tumors and stained strongly for CD117 and CD34. One patient died of disease at 35 months, one was disease free at 12 months and one was lost to follow-up. DNA extracts from 10 gastrointestinal stromal tumors (three from each of two patients and four from one patient) were subjected to polymerase chain reactions and assessed for mutations. All of the tumors were wild type for KIT exons 9, 13, and 17 and PDGFRA exons 12 and 18. Three tumors from one patient had identical point mutations in KIT exon 11, whereas the other tumors were wild type at this locus. We conclude that, although most patients with type 1 neurofibromatosis and gastrointestinal stromal tumors do not have KIT or PDGFRA mutations, KIT germline mutations might be implicated in the pathogenesis of gastrointestinal stromal tumors in some patients.

Gastrointestinal stromal tumors in patients with neurofibromatosis: imaging features with clinicopathologic correlation

OBJECTIVE

The purpose of this study was to evaluate the clinical, pathologic, and imaging features of gastrointestinal stromal tumors that occur in patients with neurofibromatosis.

CONCLUSION

Gastrointestinal stromal tumors that occur in patients with neurofibromatosis commonly originate from the proximal small intestine and are often multiple. The cross-sectional imaging appearance of gastrointestinal stromal tumors that occur in patients with neurofibromatosis is similar to that of gastrointestinal stromal tumors that occur in the general population.

Gastrointestinal Neurofibromatosis: An Unusual Cause of Gastric Outlet Obstruction

Neurofibromatosis type-1 (NF-1), also known as von Recklinghausen disease, is a common autosomal dominant condition occurring in approximately 1/3000 births. NF-1 is known to be associated with gastrointestinal neoplasms in 2–25 per cent of patients. We report the first case of gastric outlet obstruction with perforation caused by neurofibroma in a patient with NF-1. The literature is reviewed, examining 61 previously reported cases of noncarcinoid gastrointestinal (GI) neoplasms in patients with NF-1 for symptoms, location, and types of neoplasms. Neoplasms were located most often in the small intestine (72%). Neurofibromas, found in 52 per cent of patients, were the most frequently diagnosed benign neoplasms followed by leiomyomas (13%), ganglioneurofibromas (9.8%), and gastrointestinal stomal tumor (GIST) (6.5%). Adenocarcinoma was present in 23 per cent of patients. Patients with NF-1 and GI symptoms are at risk for gastrointestinal neoplasms from which symptomatic patients are likely to experience significant morbidity.

Gastrointestinal stromal tumors: radiologic features with pathologic correlation

Gastrointestinal stromal tumors (GISTs) are unique neoplasms that occur throughout the gastrointestinal tract, mesentery, omentum, and retroperitoneum. They are the most common mesenchymal neoplasm of the gastrointestinal tract and are defined by their expression of KIT (CD117), a tyrosine kinase growth factor receptor. The expression of KIT is important to distinguish GISTs from other mesenchymal neoplasms such as leiomyomas, leiomyosarcomas, schwannomas, and neurofibromas and to determine the appropriateness of KIT-inhibitor therapy. The series described herein was accumulated over 2 years and includes 64 pathologically proved GISTs (28 gastric, 27 small intestinal, six anorectal, one colonic, one esophageal, and one from the small bowel mesentery). Radiologic features of GISTs vary depending on tumor size and organ of origin. Since most GISTs arise within the muscularis propria of the stomach or intestinal wall, they most commonly have an exophytic growth pattern and manifest as dominant masses outside the organ of origin. Dominant intramural and intraluminal masses are less common radiologic manifestations. GISTs occurring in the gastrointestinal tract and mesentery characteristically have hemorrhage, necrosis, or cyst formation that appears as focal areas of low attenuation on computed tomographic images. Although the radiologic features of GISTs are often distinct from those of epithelial tumors, criteria to separate GISTs radiologically from other nonepithelial tumors have not yet been fully developed.