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1 All authors: Department of Radiology, Ankara University, School of Medicine, Talatpasa Bulvari, Sihhiye, 06100, Ankara, Turkey.
Received March 17, 2004;
accepted after revision June 8, 2004.
Address correspondence to A. Erden.
Abstract
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MATERIALS AND METHODS. Thin-collimated axial and coronal images that were originally obtained for MR cholangiopancreatography in 125 patients were reviewed by three observers individually for the presence of abdominal lymphatic confluence. The configuration, location, and dimensions of hyperintense ductal or saccular structures immediately anterior to the vertebral bodies below the diaphragma were recorded. The differences between the mean values of the diameters of the cisterna chyli obtained in the control group and in groups in which lymphatic drainage was expected to be abnormally high were compared using a one-way analysis of variance test.
RESULTS. Abdominal confluence of the lymphatics was shown in 96% of patients. The most common configuration of the cisterna chyli was tubular (42.5%). It was located at the level of L1–2 in 33% of cases and at the midline in 70%. Mean longitudinal, anteroposterior, and transverse diameters of the duct were 33.45 ± 1.74 (SD) mm, 5.23 ± 0.13 mm, and 5.23 ± 0.15 mm, respectively. No significant difference was found in the mean values of antero-posterior, transverse, and longitudinal diameters of the cisterna chyli in the control group and in the groups expected to have an increased flow into the cisterna chyli.
CONCLUSION. Abdominal confluence of lymphatics seems to be present on most of the heavily T2-weighted images. Its morphologic details and extensions can be visualized on images reconstructed with a maximum-intensity-projection algorithm. Any disorder does not necessarily lead to dilatation of these lymphatic structures.
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During the examination and postprocessing of the thin-collimation source images of MRCP, we noted high-signal-intensity sacs and ducts consistent with lymphatic channels at the prevertebral region. The bright structures we observed were the commencement of the thoracic duct or the cisterna chyli—that is, the confluence of the lymph trunks in the abdomen.
The cisterna chyli is usually situated on the front of the body of the second lumbar vertebra, to the right side and behind the aorta, by the side of the right crus of the diaphragma. It receives all lymph delivered by the union of three roots, the right and left lumbar and the intestinal trunks, before ascending into the thorax through the aortic hiatus [2].
Imaging of the lymphatic channels traditionally has been performed by bipedal lymphangiography. Recently, a projectional overview of the thoracic duct can be achieved with MRI without the use of a contrast agent [3, 4]. To the best of our knowledge, no reported investigation specifically has examined the cisterna chyli in detail with heavily T2-weighted MRI. In this study, we aimed to evaluate the detectability, configuration, size, and location of the abdominal confluence of the lymph trunks with MRCP protocol and to determine whether the disorders that have a potential to affect the abdominal lymphatic drainage could change the cisternal dimensions.
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MRI Technique
The images of the patients in whom MRCP had been performed were
retrospectively analyzed to evaluate the cisterna chyli. MRCP was performed
with a 1-T system (Signa LX Horizon, GE Healthcare) using a torso phased-array
coil. The patients were asked to fast at least 5 hr before the examination.
All sequences obtained for MRCP were used to interpret the lymphatic channels
except the thick-collimation (single-section) sequence.
Heavily T2-weighted thin-collimated images obtained in axial and coronal planes were used for measuring the dimensions of the cisterna chyli, establishing its morphology, and determining its position in relation to the midline. Three plane-localizing images and T2-weighted fast spin-echo axial images, routinely acquired in our MRCP protocol, were also reviewed in this study to locate the cisterna chyli with reference to the level of vertebrae.
MRCP was performed with a heavily T2-weighted sequence using a single-shot fast spinecho technique with respiratory gating. Initially, thin-collimation (5-mm thickness, contiguous) multisection acquisition was performed in the axial plane through the upper abdomen. After the common bile duct was localized in the axial plane, true coronal images were obtained to provide typical cholangiographic display with a section thickness of 3 mm and no intersection gap. The imaging parameters were the following: TR range (adapted automatically with software according to the patient's breathing pattern or number of slices)/TE range, 3,000–30,000/850–970; echo-train length, 25; bandwidth, 31.2 kHz; field of view, 36–46 cm; matrix size, 256 x 224–256 pixels; number of excitations, 0.5. The acquisition time for each MRCP sequence varied according to the patient's body volume and breathing rate. Additional T2-weighted fast spin-echo axial images (TR/TE, varied according to the patient's breathing pattern/102; echotrain length, 4–18) of the liver were obtained in all patients; they were used in conjunction with the localizers to display the position of the cisterna chyli. From the source image data set, maximum-intensity-projection (MIP) images of the cisterna chyli at the prespinal plane were generated mainly in the coronal plane.
Review of Data
A review of the MRCP images of 125 subjects was performed independently by
three radiologists who were blinded to patient history, clinical findings, or
the results of other tests. The images retrieved from optical disks were
analyzed at a workstation (Advantage Windows, version 3.1, Ultra 10, GE
Healthcare) according to uniform criteria that were defined and tabulated
before the reviews. A ductal or saccular hyperintense structure located in the
prevertebral region below the diaphragma was assumed to represent the cisterna
chyli. If it was present on the thin-collimated images, the properties of the
cisterna chyli were recorded on each reviewer's evaluation sheet. The
anteroposterior and transverse diameters of the cisterna chyli were measured
on heavily T2-weighted axial images or axial reformatted images at the level
of its maximal diameter. The position of the cisterna chyli in relation to the
midsagittal plane was classified into three groups using the vertebral body as
a reference (Fig. 1). The
presence of intestinal and lumbar lymphatic trunks was examined on both axial
images and reformations in the axial plane. The longitudinal diameter of the
cisterna chyli was measured on 3D coronal reconstructions obtained with a MIP
algorithm. The shape of the duct was established on 3D reconstructions, and
its various configurations were named with terms similar to those previously
defined at lymphangiographic examinations
[5]. After marking out the
levels of superior and inferior boundaries of the cisterna chyli with cursors
on MIP images, we used localizers and T2-weighted fast spin-echo axial images
to determine the level of the cisterna chyli with reference to the spine. Any
discrepancies between reviewers were resolved by consensus review. Additional
retroperitoneal abnormalities (scoliosis, retroperitoneal lymph node
enlargement, tortuosity of the abdominal aorta, an aneurysm of the abdominal
aorta, and a horseshoe kidney), if present, were also noted.
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Furthermore, data analysis was performed to establish whether any significant differences were present in the anteroposterior, transverse, and longitudinal diameters of the cisterna chyli in patients with and without abnormally affected lymphatic drainage. To evaluate this hypothesis, we grouped 41 patients of the 125 according to their final diagnosis as follows: group I (n = 19), patients with normal MRCP findings in whom further investigation showed no abnormality in any organ system (control group), and group II (n = 12), patients who had diseases that could affect the generalized lymphatic drainage of the abdomen. Of these 12 patients, five had portal hypertension due to liver cirrhosis, three had acute pancreatitis, three had malignant lymphoid disorders, and one had congestive heart failure. Group III (n = 10) comprised patients with obstructions in the extrahepatic bile ducts leading to dilatation of intrahepatic bile ducts and increase in local lymph flow. Of these patients, three had carcinoma of the pancreatic head, three had cholangiocarcinoma, two had choledocholithiasis, one had chronic pancreatitis, and one had a benign stricture in the distal common bile duct.
Statistical Analysis
The average of measurements obtained by three reviewers was used for
statistical analysis. The results were reported as means (± SD).
Normality assumption was met for three variables (anteroposterior, transverse,
and longitudinal diameters). For this reason, the differences between the mean
values of the diameters of the cisterna chyli obtained in the three groups
mentioned previously were compared using a one-way analysis of variance test.
A p value of less than 0.05 was considered statistically
significant.
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Configuration
The appearance of the cisterna chyli was variable, and classification by
shape was quite subjective. In 51 (42.5%) of 120 patients, it had a tubular
(linear) shape, but the shape may be plexiform (n = 23), deltaic
(n = 15), or other (n = 31; fusiform, inverted V, Y-shaped,
beaded, triangular sigmoidal, commalike, and nodular) (Figs.
4,
5,
6A,
6B,
7,
8).
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Location
The cisterna chyli was situated approximately in the midline in 70% of the
cases (Fig. 1). It was slightly
to the right side of the midline in 24 cases (20%) and to the left side in 17
cases (14.2%). It was located between the L1 and L2 levels in 40 cases
(33.3%). Its cephalic and caudal boundaries were at any level between the T10
and L4 vertebrae (Table 1).
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Dimensions
The mean craniocaudal length of the cisterna chyli was 33.45 ± 1.74
mm (range, 3.5–102 mm). The anteroposterior diameter ranged from 2 to 10
mm with a mean of 5.23 ± 0.13 mm. The mean transverse diameter was 5.23
± 0.15 mm (range, 2–10 mm). We could not find any significant
difference (p > 0.05) in the mean values of anteroposterior,
transverse, and longitudinal diameters of the cisterna chyli in the control
group and in the groups expected to have an increased flow into the cisterna
chyli (Table 2).
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Heavily T2-weighted MRI findings showed a much greater incidence of the cisterna chyli than was reported for lymphangiography and CT. In our study, we could identify the abdominal confluence of lymphatic trunks and cisterna chyli in 96% of the cases. The advantages high contrast and high signal intensity) provided by heavily T2-weighted MRI, thin collimation, and 3D reconstruction in the main orthogonal planes yielded a higher incidence of visualization than that in previously reported figures. Because of its retrocrural location, the ductal visibility was not degraded by possible overlap of other fluid-containing organs, diaphragmatic movements, and intestinal peristalsis.
The conventional lymphangiographic appearance of the cisterna chyli is variable; the basic forms are bulbous, plexiform, inverted Y, inverted V, a rope of pearls, or commalike [5]. It is generally defined as tubular, rounded, elliptic, or lobulated on cross-sectional images [6, 9, 10]. Because of its complex 3D shape, we encountered a variety of appearances on heavily T2-weighted images in our study. The cisterna chyli most often had a tubular (linear) morphologic appearance, but the miscellaneous configurations, including plexiform, deltaic, beaded, or triangular were also seen. Besides the presence of the contractions and the effect of the postprandial status, the perceptional differences of the observers may also change the name given to a specific morphology.
The combination of a single-shot fast spinecho sequence and the torso phased-array coil makes it possible to visualize ducts as small as 1 mm in diameter on MRCP [11]. Although they have very small diameters, the lumbar lymphatic trunks and intestinal trunk (lacteal) are the main intraabdominal tributaries of the cisterna chyli [2, 12]. The rate of detectability of the intestinal and lumbar trunks in our series was 13.6% and 70%, respectively. To our knowledge, no published report describes the radiologic appearance of the intestinal lymphatic trunks. The intestinal trunk was visualized anterior to the cisterna chyli where it pierces the diaphragmatic crus. Its mesenteric course could not be traced because of its fine caliber. The radiologic data concerning the lumbar lymphatic trunks are more detailed. These structures can be identified on both sides of the vertebral body. Williams et al. [13] reported that this channel can be detected in 4% of the CT examinations (a figure significantly lower than ours) as bilateral paraaortic fluid-dense structures measuring from 3 to 8 mm in diameter between the L1 and L3 levels. The dilatation of lumbar lymphatic trunks is generally assumed to be a disorder and should be differentiated from lymphadenopathy [10, 14, 15]. The left-sided cisterna chyli may have an appearance similar to that of the varicose left lumbar lymphatic trunk [6].
The lymphatics of the liver also receive attention in conditions leading to hepatic periportal lymphedema [17]. More than 80% of the lymph from the liver is drained by collecting vessels that run along the portal triad. These collecting vessels eventually drain into the cisterna chyli [18]. We observed deep hepatic lymphatics in a patient with acute nonlymphocytic leukemia who had periportal cuffing on MRI (Fig. 6B).
The size of the cisterna chyli also shows a wide range of variations. Rosenberger and Abrams [5] reported that the cisterna chyli was usually less than 5 cm in length. In 27% of their cases, it was greater than 5 cm. In our study population, the mean length of the cisterna chyli was 3.3 cm, ranging from 0.3 to 10 cm. We determined that the anteroposterior and transverse diameters were very close to each other (0.5 cm) with a range between 2 and 10 mm. These data agree with those in article by Smith and Grigoropoulos [6].
It is important to determine whether a cisternal diameter greater than the mean values is an indicator of a disorder or a normal variation. In some instances, an appearance similar to a lymphocele formed by a cluster of lymphatics can be seen in healthy individuals [5]. The dimensions can be influenced by the phases of the respiration and postprandial status. We examined the patients after 5 hr of fasting and acquired the data during the same phase of the respiration (the scan is triggered at end-expiration). The state of hydration [9] and lymphatic contractions [5, 12] can also influence the size and shape of the cisternachyli.An increase in lymph drainage into the cisterna chyli is expected in portal hypertension due to cirrhosis [4, 19], congestive heart failure [17], acute pancreatitis [20, 21], and malignant lymphoid disorders [20]. Experimental ligation of the common bile duct has also increased lymph flow up to three times its value before ligation [18]. Depending on these data, we grouped and compared the mean values of anteroposterior, transverse, and longitudinal diameters of the cisterna chyli in three different groups and found no significant difference between the data of the control group and that of the patients expected to have an increased lymphatic drainage into the cisterna chyli. Because of the wide range of normal variations, size has not been useful as a single determinant of disease. In addition, our study was not designed to analyze the dimensional changes of the cisterna chyli in specific pathologic conditions. Consequently, the groups were rather heterogenous, and the number of the patients was small.
The cisterna chyli is anatomically described as situated at the level of the L1 and L2 vertebrae [2]. In 74 of 204 cases, Rosenberger and Abrams [5] found it to be located at the same level at which Smith and Grigoropoulos [6] detected it, a variable location between T11 and L2 (n = 7), and Gollub and Castellino [9] determined its location as the T12–L1 interspace in 11 of 18 cases. The most frequent location in our study was at the level between the L1–2 vertebrae, which is consistent with prior observations.
An enlarged necrotic lymph node or tumor recurrence may mimic the cisterna chyli on cross-sectional techniques [9, 10]. The retroperitoneal structures, which appear hyperintense on heavily T2-weighted images, include the ureter, ascending lumbar veins, and the gonadal vein with slow flow. According to our observations, the inferior mesenteric vein, the left-sided inferior vena cava, and the retroaortic left renal vein have no potential to simulate lymphatic ducts on heavily T2-weighted images, especially when the images reformatted in orthogonal planes were analyzed.
In conclusion, the cisterna chyli seems to be present on most heavily T2-weighted images. However, the contributing lymphatics normally vary so widely in shape, orientation, and size that few appear exactly alike on heavily T2-weighted images, and they are usually not seen in their entirety on a single source image. After reconstruction with an MIP algorithm, the details regarding the morphology of the abdominal confluence of the lymph trunks can be visualized easily and the full length of the ducts can be depicted, similar to structures seen on conventional lymphangiograms. Any disorder does not necessarily lead to dilatation of these lymphatic structures. Awareness of their appearances increases their recognition and allows differentiating them from normal and abnormal structures.
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-glutamyltransferase. Coronal
maximum-intensity-projection image shows several branches of lymphatics
joining slightly to left of aorta to form plexiform interlacement
(arrows).