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Original Report |
1 Department of Radiology, Seoul National University College of Medicine,
Institute of Radiation Medicine, Seoul National University Medical Research
Center, and Clinical Research Institute, Seoul National University Hospital,
28 Yongon-dong, Chongno-gu, Seoul 110-744, Korea.
2 Department of Radiology, Asan Medical Center, University of Ulsan College of
Medicine, Seoul, Korea.
3 Department of Pathology, Seoul National University College of Medicine, Seoul
National University Hospital, Seoul, Korea.
Received November 27, 2003;
accepted after revision January 21, 2004.
Supported in part by the 2003 BK21 Project for Medicine, Dentistry, and
Pharmacy.
Abstract
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CONCLUSION. Gastrointestinal stromal tumors of the duodenum appear on barium studies as extrinsically compressing or submucosal masses with or without ulceration. These tumors usually appear on contrast-enhanced CT as well-defined masses with an exoenteric growth pattern and relatively good heterogeneous enhancement.
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Gastrointestinal stromal tumors most frequently occur in the stomach (60–70%) followed by the small intestine (20–30%), colorectum (10%), and esophagus (< 5%) [1]. Although the radiologic findings of gastrointestinal stromal tumors have been described recently in the radiology literature [1, 4–6], the radiologic features of gastrointestinal stromal tumors resemble those of leiomyomas or leiomyosarcomas, as has also been previously described [7, 8]. However, to our knowledge, the radiology literature is limited regarding the imaging appearance of gastrointestinal stromal tumors of the duodenum, and no large series focusing on gastrointestinal stromal tumors of the duodenum has been reported. The purpose of our study was to describe the CT and radiographic findings of gastrointestinal stromal tumors of the duodenum.
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CT examinations were performed using a Somatom Plus-4 (Siemens Medical Systems) or a HiSpeed Advantage (GE Healthcare) scanner. Each patient received 120 mL of a nonionic contrast material (Ul-travist 370 [iopromide], Schering) through an 18-gauge angiographic catheter inserted into a forearm vein. The contrast material was injected at a rate of 2.5 mL/sec using an automatic injector. Helical CT was performed in each patient using the following parameters: a 5- or 7-mm collimation, 1:1 table pitch, and 5- or 7-mm reconstruction interval. In seven patients, biphasic helical CT scans were obtained 30 (arterial phase) and 70 (portal venous phase) sec after the initiation of the contrast material injection. In 13 patients, monophasic helical CT scans were obtained with a 60- to 70-sec scanning delay (portal venous phase). An upper gastrointestinal series was performed in 17 patients.
Two radiologists reviewed all the radiologic studies retrospectively, and final interpretations were reached by consensus. Radiographic findings on barium studies were reviewed to evaluate tumor location, ulceration, and morphologic characteristics. We reviewed only the CT scans that had been obtained during the portal venous phase for the tumor evaluation, whereas we assessed all the CT scans for the metastasis evaluation. CT scans were reviewed to determine the size, shape, margin, and pattern and degree of enhancement of the tumors; the presence of ulceration and calcification within the lesions; and the pattern of tumor growth (endoluminal, mixed, or exoenteric). Tumor margins were categorized as well defined (a smooth or lobular contour without surface projections), irregular (with surface projections), or clearly invasive (when soft tissue of a similar attenuation to that of the tumor penetrated an adjacent organ). An endoluminal growth pattern was defined to be present if the tumor mass attached to the bowel wall was completely confined to the bowel lumen without bulging into the extraluminal space. Conversely, an exoenteric growth pattern was defined to be present if the mass was confined to the extraluminal space without bulging into the bowel lumen, although extrinsic indentation was observed. A mixed growth pattern was defined as a typical dumbbell appearance. The degree of enhancement was judged in comparison with that of muscle and liver: poor enhancement, identical to or less than that of muscle; moderate enhancement, more than that of muscle but less than that of liver; and good enhancement, identical to or more than that of liver. CT findings were also evaluated for bowel obstruction, bile duct dilatation, abdominal lymphadenopathy, ascites, and distant metastasis.
The pathology records of all patients were reviewed to establish mitotic activity and tumor immunoreactivity to CD117. On the basis of previous studies on gastrointestinal stromal tumors [9], the criteria of benignity and malignancy were defined. The histopathologic findings in surgical specimens were retrospectively reviewed by one gastrointestinal pathologist with an emphasis on the detection of hemorrhage, necrosis, or cystic degeneration. A direct comparison between imaging and histopathologic findings was performed by another pathologist, and two radiologists reviewed the pathology reports, photographs of gross specimens, and microscopic examinations.
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On barium studies, eight of the 17 tumors had ulceration. Six tumors, having ulceration (n = 3) or not (n = 3), appeared to be smoothly marginated mural-based masses that formed obtuse angles with the duodenal wall and were compatible with submucosal tumor (Figs. 1A and 1B). Eleven tumors appeared as an extrinsic compression with (n = 5) (Figs. 2A and 2B) or without (n = 6) ulceration.
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On CT scans, tumors ranged from 2.5 to 13 cm in greatest dimension (mean, 7.2 cm) and 13 tumors (65%) were larger than 5 cm. The 20 gastrointestinal stromal tumors were located in the first (n = 1), second (n = 9), third (n = 8), or fourth (n = 2) portion of the duodenum. Seven tumors (35%) were smooth (Fig. 3), whereas 13 tumors (65%) had a lobulated contour (Fig. 4). The tumor margin was well defined in 16 tumors (80%), and two tumors (10%) had an irregular margin; the remaining two (10%) had invaded renal vessels (Fig. 4) and the ascending colon, respectively. Six tumors (30%) had a mixed growth pattern, and 14 tumors (70%) showed an exoenteric growth pattern. In five of six tumors showing a mixed growth pattern, the extraluminal portion comprised most of the tumor volume. Two tumors (10%) showed a homogeneous enhancement pattern (Fig. 3), but 18 tumors (90%) showed a heterogeneous pattern. Seven tumors (35%) had good enhancement, 11 (55%) had moderate enhancement, and two (10%) had poor enhancement. On CT, ulceration was observed in six patients and air–fluid level was observed in three patients (Fig. 2B). Calcification was observed in one tumor.
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No patients had lymphadenopathy or ascites. Duodenal obstruction was detected in one patient. Liver metastases were present in five patients. Metastatic lesions in the liver were hypoattenuating during the portal venous phase in four patients, and metastatic lesions were isoattenuating during the portal venous phase and hyperattenuating during the arterial phase in the fifth patient (Figs. 5A, 5B, and 5C). The bile duct was dilated in four patients, and two patients underwent percutaneous transhepatic biliary drainage due to hyperbilirubinemia before surgery.
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Immunohistochemical studies showed CD117 expression in all patients. Of the 20 gastrointestinal stromal tumors of the duodenum, five were classified as having low malignant potential and 15 as being malignant. Gross specimens of 14 tumors were available for review. Of the two tumors that showed homogeneous attenuation on CT, one was a solid tumor without hemorrhage or necrosis at pathologic examination and the other was a solid tumor containing multiple punctate hemorrhages. In 12 tumors with heterogeneous attenuation on CT scans, central areas of low attenuation were found to correspond to necrosis with hemorrhage (n = 10), the solid tumor itself (n = 1), or fluid in an ulcer (n = 1).
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A malignant gastrointestinal stromal tumor appears as a large well-circumscribed tumor that is usually predominantly extraluminal and has a heterogeneously enhancing soft-tissue rim surrounding a necrotic center [1, 4, 5]. Benign gastrointestinal stromal tumors are often small round or ovoid tumors that are usually endoluminal and have a homogeneous enhancing pattern [5, 7, 8]. Generally speaking, the radiologic features of gastrointestinal stromal tumors of the duodenum seem to be similar to those that occur in the remainder of the gastrointestinal tract. In our series, most gastrointestinal stromal tumors of the duodenum—even small ones—grew in an extraluminal direction and showed heteroge neous attenuation on CT, whereas other small gastric gastrointestinal stromal tumors have often shown an endoluminal growth pattern and homogeneous attenuation [8].
The liver is the most common metastatic site at both presentation and disease relapse [4]. On CT scans obtained during the portal venous phase, metastasis in the liver was usually hypoattenuated compared with the normal surrounding liver [4, 11]. In our series, one patient had multiple small liver metastases that were isoattenuating on CT during the portal venous phase and hyperattenuating during the arterial phase. We may have missed some hypervascular liver metastases, because biphasic CT was undertaken in only seven of the 20 patients. The availability of the tyrosine kinase inhibitor has markedly altered the clinical approach to gastrointestinal stromal tumor, and this inhibitor has been proven effective in the management of metastatic gastrointestinal stromal tumor [3]. Therefore, the detection of liver metastasis has become more important than ever. Additional studies may be needed to determine whether biphasic helical CT can detect more liver metastases than monophasic helical CT in patients with gastrointestinal stromal tumors.
It may be difficult to determine the organ of origin of a significant exoenteric tumor from the duodenum using cross-sectional imaging alone. For example, the differentiation of a tumor located between the duodenum and the pancreas may be difficult. A gastrointestinal stromal tumor of the duodenum appears as a well-defined mass with heterogeneous attenuation, whereas a pancreatic tumor commonly appears as an ill-defined mass with poor enhancement. However, a solid pseudopapillary tumor of the pancreas may have features resembling those of a gastrointestinal stromal tumor of the duodenum, such as a well-encapsulated mass with hemorrhage [12]. An intact displaced pancreas head can be observed in patients with a gastrointestinal stromal tumor of the duodenum, whereas the appearance of a pancreas with a "beak" suggests a pancreatic origin in patients with a solid pseudopapillary tumor of the pancreas. We also believe that central gas and a cavitary mass militate against the diagnosis of a pancreatic tumor.
The differential diagnosis for gastrointestinal stromal tumors of the duodenum includes primary and metastatic duodenal neoplasms. Adenocarcinoma is the most common primary malignancy of the duodenum and typically manifests as an annular narrowing with abrupt concentric or irregular overhanging edges or as a polypoid tumor mass. Thus, its appearance usually does not overlap with that of gastrointestinal stromal tumors [13]. Lymphomas may produce large ulcerative or cavitary masses that may be indistinguishable from gastrointestinal stromal tumors on radiologic images. However, the presence of associated lymphadenopathy favors a diagnosis of lymphoma. Carcinoid tumors may appear as ill-defined, homogeneous masses with displaced bowel loops. Paragangliomas are soft-tissue-attenuation masses with homogeneous enhancement and appear as smoothly margined dumbbell-shaped masses [14] that could be confused with gastrointestinal stromal tumors of the duodenum.
In conclusion, gastrointestinal stromal tumors of the duodenum appear on barium studies as extrinsically compressing or submucosal masses with or without ulceration. The common CT findings of gastrointestinal stromal tumors of the duodenum are well-defined exoenteric masses that usually consist of an irregular central area of low attenuation surrounded by variously thickened soft-tissue-density walls with or without ulceration.
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