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Original Report |
Department of Pediatric Radiology, University Hospital La Paz, Paseo de la Castellana, 261, Madrid 28046, Spain.
Received March 11, 2004;
accepted after revision July 23, 2004.
Address correspondence to T. Berrocal
(tberrocal.hulp{at}salud.madrid.org).
Abstract
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CONCLUSION. CT and MRI essentially confirmed the findings of sonography in all cases, providing no relevant additional information about the nature, internal structure, or content of the cysts. When pancreatic macrocysts are clearly shown on sonography in asymptomatic patients with CF, no additional imaging is warranted.
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Although lung disease is the leading cause of morbidity and death in patients with CF, improved survival rates lead to increased morbidity in other organs and shift the attention to other complications, for example, gastrointestinal disease [3].
Pancreatic involvement can result in exocrine or endocrine insufficiency [1, 2]. The spectrum of pancreatic appearances has been described as follows: complete replacement of the pancreas by fibrofatty tissue, with enlargement of the pancreas corresponding to lipomatous pseudohypertrophy [4]; partial replacement of the pancreas by fibrofatty tissue; complete atrophy of the pancreas without fatty replacement; diffuse pancreatic fibrosis; and cystic transformation of the pancreas [5, 6]. Calcifications may also be found [7]. The abnormal changes in the pancreas are a function of the duration and intensity of the CF disease [3]. Cysts are a relatively common feature in the CF-affected pancreas, but their size does not usually exceed a few millimeters. Macroscopic cysts measuring more than 1 cm are a rare condition [1, 8-11]. Macrocysts of different sizes distributed throughout the gland represent an extremely unusual form of pancreatic involvement in CF that has been described in only a few patients and is known as pancreatic cystosis [12, 13].
The purpose of this article is to analyze and describe the sonographic, CT, and MRI findings of pancreatic cystosis and to evaluate the role of these imaging techniques in the management of this condition.
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This research was approved by the ethics committee of our hospital, and informed consent was obtained in all cases. Sonography was performed in a standardized manner after the patients had fasted at least 7 hr. A Power Vision sonography machine (Toshiba Medical Systems) was used with a 3.5- or 5-MHz sector transducer or a 7.5-MHz linear array transducer. With the patient in the supine decubitus position, systematic longitudinal and transverse scans were obtained throughout the entire pancreatic gland, paying attention to the size, shape, and echo pattern of the pancreas. Measurements of the pancreas were obtained with transverse scanning. The greatest anteroposterior diameters of the head, body, and tail were measured and compared with standardized age-related dimensions of the pancreas [11]. Assessment of the pancreatic cysts included anteroposterior, transverse, and longitudinal diameter measurements and study of the wall thickness, presence of nodules or solid foci, and internal echotexture. Single helical CT examinations were performed on a Somaton Plus scanner (Siemens) in accordance with our routine departmental protocol. Contrast medium was given orally before the examinations. Abdominal scans then were obtained before and after IV contrast injection. Contrast material (2 mL/kg) was administered by bolus injection. Five millimeters of collimation at an interval of 5 mm were the imaging parameters. Cysts were assessed for size, wall thickness and enhancement, internal structure, and attenuation values of their liquid content. The existence of calcifications of the cyst walls was also assessed.
MR images were acquired on a 1.5-T Magnetom Vision imaging unit (Siemens), using a body coil. MRI was performed with 3- to 6-mm-thick sections, using axial T1-weighted fast low-angle shot (FLASH) with and without fat saturation (TR/TE, 149/4.1; flip angle, 80°), axial and coronal T2-weighted HASTE (TE, 90; flip angle, 150°), and turbo spin-echo (2,800/1,100; flip angle, 150°) sequences. Cystic lesions were assessed for size, signal intensity, nodules or solid foci, and wall enhancement after gadolinium administration. The presence or absence of identifiable pancreatic tissue was also noted. For all techniques, lesions were measured with electronic calipers. Sonographic, CT, and MR images were evaluated by two radiologists who were experienced in CF, and conclusions were reached by consensus.
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On CT scans, cysts were well-defined lesions with sharply circumscribed smooth walls; 81% of the lesions showed water-density homogeneous content (Figs. 3A, and 3B), and the rest showed a slightly higher attenuation value, ranging between 20 and 33 H. The content of the cysts was always homogeneous; no fluid-fluid levels were observed on CT scans. Three patients showed small areas of pancreatic tissue with low attenuation values (ranging between -170 and -40 H) between the cysts that were consistent with fat replacement. In two patients with complete replacement of the pancreas by macrocysts, no pancreatic tissue could be identified. Small calcifications were shown in the pancreatic body of one patient who had a large cystic lesion in the head of the pancreas. No calcifications were observed in the walls of the cysts in any patient.
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On MRI, the cystic lesions showed high signal intensity on T2-weighted images and marked hypointensity when compared with normal pancreatic tissue on T1-weighted images. A fluid-fluid level was observed in two uniloculated cysts, one measuring 3.2 cm and the other 4.6 cm, on MRI. The walls of the cysts were always thin and smooth; no nodules, excrescences, or solid foci were found. No dilated pancreatic ducts were observed on MRI in any patient.
When comparing the results from sonography, CT, and MRI, we found that cystic lesions larger than 1 cm were adequately revealed on the three imaging techniques. In those patients exhibiting complete cystic replacement of the pancreas by cysts, MRI showed a larger number of small cysts and depicted the pancreatic outline more clearly. In patients without complete cystic transformation, MRI depicted several small cystic lesions beside larger ones that were not shown on sonography or CT. Cystic structure as shown on all three techniques consisted of thin walls without any outgrowths or solid portions. Neither CT nor MRI provided clinically useful findings that were different from those already seen on sonography.
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Pancreatic changes depend on the duration and intensity of CF disease [3] but not on the genetic type [15]. Diffuse fatty replacement and decreased pancreatic glandular tissue are more often found in older patients and represent an end-stage disease of the pancreas, paralleling pancreatic exocrine dysfunction [16]. The increased life expectancy of CF patients that has resulted from more effective management of respiratory disease over the past decades has led to a rise in the prevalence of complications in other organs, some of which are life-threatening [2].
The abnormal changes in the pancreas of CF patients can be seen on multiple imaging techniques. Each imaging technique has a role in the assessment of pancreatic involvement during the course of CF. Sonography remains the technique of choice for initial evaluation of the pancreas in patients with CF because it is a fast, accurate, and noninvasive imaging technique that does not require sedation of the pediatric patient and allows examination of the adjacent organs [11]. An increase in pancreatic echogenicity, resembling echogenicity of the retroperitoneal fat, and a decrease in pancreatic size with the typical fine-lobular (cobblestone-like) echo pattern of the pancreas no longer detectable are the classic sonographic findings [3, 11]. Complete replacement of the pancreas by fat is visualized on CT scans as an increase in pancreatic size with low attenuation values and on MR images as an enlarged pancreas with high signal intensity on T1-weighted images. Complete pancreatic atrophy without any fatty replacement can also be found. In those cases, the pancreas shows a decreased size with soft-tissue attenuation without scattered areas of fat attenuation or high signal intensity. Areas of fibrosis exhibit low attenuation values with no contrast enhancement on CT images and a low signal intensity on both T1- and T2-weighted MR images [17]. Complete pancreatic fibrosis and calcifications within the pancreas can also be found [5, 7].
Sonographic findings of pancreatic cystosis reported in the literature are similar to those found in our patients, with multiple, thin-walled, sonolucent, multiloculated masses extending from the porta hepatis to the splenic hilum [1, 8, 11, 12, 15] and hyperechoic scattered pancreatic tissue between cysts (Figs. 1, 2A and 2B). In our series, CT accurately showed the various pancreatic changes that can be found in patients with CF [8, 12, 15, 16], including small calcifications and an absence of identifiable pancreatic tissue when complete replacement of the pancreas by macrocysts occurred. No solid portions or excrescences were seen within the cysts in any case. However, CT did not provide any relevant additional information that was not already known from the sonographic findings. Because CT has the disadvantage of using ionizing radiation, it should not be used routinely in patients with CF. CT may be useful if the pancreas cannot be reliably examined with sonography (as is the case in patients with excessive abdominal gas) or if a complication is suspected, mainly hemorrhage or an infection.
MRI of pancreatic macrocysts in CF has been previously reported only in a few patients [12, 13, 17]. In our patients, cystic content showed homogeneous low signal intensity, significantly lower than that of the pancreatic tissue on T1-weighted FLASH sequences with and without fat saturation. On HASTE sequences, cystic content showed very high signal intensity with thin, regular, and linear low-signal-intensity walls in all cases. The higher soft-tissue contrast of MRI allows us to infer the fluid content of the cyst that results in low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. No solid excrescences were seen on MR images either. One disadvantage of MRI is that its ability to show the small pancreatic calcifications that may be found in CF is not as great as those of other imaging techniques [6]. Although additional small cysts were seen on MRI that were not visible on CT and sonography, no additional clinically important information was added to that already obtained with sonography.
Our study has limitations. Probably MR cholangiopancreatographic examinations with thicker slabs in coronal, sagittal, and oblique planes and CT reformations in longitudinal planes would have shown whether these cystic lesions actually are interconnected or are in continuity with dilated ducts.
The imaging features of pancreatic macrocysts seen in our patients are similar to those of uncomplicated pancreatic cysts from any other cause. No parietal cyst calcifications were present in our series. A parietal calcification in one cyst and evidence of hemorrhage in another cyst during an observation period in one CF patient with pancreatic cystosis have been reported using sonography and CT [15].
None of our patients suffered abdominal manifestations attributable to pancreatic cysts. The reviewed literature contains reports of patients with pancreatic cysts who had clinical manifestations that may be explained by a mass effect within the abdomen [8, 12, 13, 18]. The real difficulty in the interpretation of those cases was that imaging studies were done when the patients had pain, and the cysts were found at that time. That does not mean the cysts were the cause of pain because they might have been present for years.
Asymptomatic patients in whom pancreatic cystosis was diagnosed during routine abdominal sonography may require only follow-up of this incidental finding, especially if no history of trauma or pancreatitis exists to suggest pseudocysts, as occurred in our patients. A similar cystic transformation and enlargement of the pancreas have been described occasionally in polycystic kidney disease and von Hippel-Lindau disease and in rare neoplasms such as lymphangiomas and mucinous cystadenomas [19]. The macrocysts in pancreatic cystosis can exhibit findings identical on imaging to the ones found in those diseases; however, the clinical context of CF easily rules out other diagnoses. Polycystic disease also can be excluded on the basis of the normal appearance of the kidneys. Pathologically, pancreatic involvement in polycystic disease differs from pancreatic involvement in CF in that the main pancreatic ducts form multilocular cavities and the acini remain intact [8]. Mucinous cystadenomas occur more frequently in woman between the ages of 40 and 60 years and may be of high signal intensity on T1-weighted images due to the presence of mucin. To the best of our knowledge, no cases of malignant transformation of pancreatic cystosis in CF have been reported. Therefore, when pancreatic macrocysts are clearly depicted on imaging in a patient with CF, other diagnoses such as neoplasms need not be invoked [8, 12, 13].
In conclusion, pancreatic cystosis is a rare manifestation of CF and is thought to be caused by ductal dilatation resulting from ductal protein precipitation. The diagnosis can easily be made in the appropriate clinical setting by means of sonography, CT, or MRI; however, sonography should be the technique of choice for initial and follow-up evaluation of patients with these findings. Although CT and MRI allow an adequate assessment of the structure and content of the cysts and a more panoramic view of the pancreas than sonography, they do not provide any relevant additional information to the data provided by sonography. Therefore, when this appearance is found sonographically in an asymptomatic patient with CF, no additional imaging is needed. CT in particular should be avoided because it exposes the patient to radiation. When macroscopic cysts are found in a patient with CF who is undergoing scanning for other reasons, pancreatic cystosis should be suspected and follow-up with sonography should be recommended.
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