|
|
||||||||
Ann Thorac Surg 2005;79:1866-1871
© 2005 The Society of Thoracic Surgeons
a Department of Thoracic Surgery, Numazu City Hospital, Numazu, Shizuoka
b First Department of Surgery, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan
Accepted for publication December 20, 2004.
* Address reprint requests to Dr Asai, Department of Thoracic Surgery, Numazu City Hospital, 550 Harunoki Higashi-shiiji, Numazu, Shizuoka, 410-0302 Japan (E-mail: asaik{at}msc.biglobe.ne.jp).
| Abstract |
|---|
|
|
|---|
METHODS: Chest computed tomographic images and medical records of 725 patients were retrospectively reviewed. The frequency, drainage pattern, diameter, and associated anatomical characteristics of the UVPBI were assessed, and our right thoracotomy cases with the UVPBI were examined.
RESULTS: The UVPBI was found in 41 (5.7%) of 725 computed tomography cases, and in 9 (3.9%) of 230 right thoracotomy cases. Three UVPBI drainage sites were observed: (1) the superior pulmonary vein group, 55%; (2) the inferior pulmonary vein group, 41%; and (3) the superior segmental vein group, 4%. The diameter of the UVPBI at the level of the bronchus intermedius ranged from 1 to 7 mm (4.1 ± 1.6 mm). The diameter of the UVPBI in the superior pulmonary vein group was significantly greater than that in the inferior pulmonary vein group (p < 0.01). The prevalence of a central vein was 43.9% for all UVPBI cases and 15.8% for large UVPBI cases (
5 mm in diameter). Of the 9 right thoracotomy patients, 1 suffered UVPBI injury; this patients UVPBI was not identified either preoperatively or intraoperatively.
CONCLUSIONS: The UVPBI is not as rare as was previously believed. It can be a main drainage route of the right upper lobe. Preoperative identification of this venous variation by computed tomography is useful for safe and accurate surgical procedures.
| Introduction |
|---|
|
|
|---|
| Patients and Methods |
|---|
|
|
|---|
The CT analysis for UVPBI identification consisted of the following three processes: (1) evaluation of the presence of nodular opacities attached posterior to the bronchus intermedius; (2) confirmation that the nodular opacities were veins by tracing the continuity of the nodule both cranially and caudally on contiguous CT slices; and (3) determination as to which lobe from which the vein drained (ie, the right upper or lower lobe). Depending on the drainage lobe, the vein was classified as either a UVPBI or as a right lower lobe vein posterior to the bronchus intermedius (LVPBI). The LVPBI was regarded as a branch of the right superior segmental vein (V6).
The UVPBI was rigorously limited to the pulmonary vein, which could "apparently" be followed peripherally into the lung parenchyma of the right upper lobe. Furthermore, after identifying the UVPBI, we grouped them according to their courses towards the left atrium (LA) beyond the posterior wall of the bronchus intermedius. We evaluated the frequency of the UVPBI both in the whole population and in patients who had undergone a right thoracotomy, and we also measured the diameter of the UVPBI in each course group. In UVPBI cases, paying special attention to the fact that the central vein was prevalent in the right upper lobe, which was easily identified by CT, we checked for the presence of a central vein to determine the influence of the UVPBI on the whole drainage pattern in the right upper lobe, to the extent that we could determine this from CT study. The diameter of the UVPBI was measured at the level posterior to the bronchus intermedius. Whenever the nodular opacity was not round, the short-axis diameter was used for measurements. When the bronchus intermedius and the attached nodular opacities were observed in two or more contiguous CT slices, the maximum diameter was used.
From a total of 780 computed tomographic images, 55 were excluded because of the absence of normal lung parenchyma necessary to identify anatomical structures in the relevant area. Thus, the study consisted of 725 eligible computed tomographic examinations (457 men, 268 women; age range, 6 to 89 years; mean age, 60 years). The reasons for exclusions were as follows: right pneumothorax (19), pleural effusion (3), tumor (11), inflammation (7), bulla (4), contusion (5), previous right-side pulmonary resection (4), right-sided thoracic aorta (1), and dextrocardia (1).
Of the total 725 patients, 422 (58.2%) underwent surgery, 230 (31.7%) had a right thoracotomy (including surgical procedures by thoracoscopy and median sternotomy), and 137 (18.9%) had a right-sided major pulmonary resection (segmentectomy, lobectomy, and pneumonectomy).
All vessel diameter measurements were recorded as mean ± standard deviation. Students t test and Fishers exact probability test were used for comparisons between groups. A p value of less than 0.05 was considered statistically significant.
| Results |
|---|
|
|
|---|
UVPBI was broadly classified according to its course towards the LA beyond the posterior wall of the bronchus intermedius. The superior pulmonary vein (SPV) group included cases in which the UVPBI ran horizontally into the mediastinum. In the remaining UVPBI cases, the UVPBI ran vertically into the inferior pulmonary vein (IPV) or V6 while in contact with the posterior wall of the bronchus intermedius and the lower lobe bronchus. These cases were classified into two groups: (1) the IPV group (when the UVPBI joined the inferior pulmonary vein), and (2) the V6 group (when a common trunk of UVPBI and V6 joined the LA independently). Thus, the UVPBI cases comprised three drainage variation groups: (1) SPV group, (2) IPV group, and (3) V6 group (Fig 1). Concerning the SPV group, since the exact course of the UVPBI within the mediastinum could not be detected by the lung window setting CT study, that portion of its course had to be deduced and supported by our limited contrast-enhanced, thin-section CT study, previous studies, and case reports.
|
5 mm in diameter) than for cases with a small UVPBI (< 5 mm in diameter) (p < 0.01). In particular, in large UVPBI cases within the SPV group, the prevalence of a central vein was only 8.3%. All UVPBI cases were drainage veins from the posterior segment.
|
|
|
|
| Comment |
|---|
|
|
|---|
Identifying pulmonary vessels by CT, especially at the hila, can sometimes be very difficult because of their complex anatomy. While three-dimensional images can more clearly depict pulmonary vessels [13], CT can also identify pulmonary vessels in certain areas. For instance, CT can clearly depict the posterior wall of the bronchus intermedius, sharply outlined by air in the bronchial lumen and lungs, and usually no other structure is behind it, except lung parenchyma. When CT visualizes a nodular opacity behind the tangentially depicted posterior wall of the bronchus intermedius, the UVPBI or LVPBI can be identified without much difficulty by careful tracing of the continuity of the nodule cranially and caudally.
Before the advent of CT, Boyden [14] in 1955 and Yamashita [15] in 1978 described the details of the segmental anatomy of the lung in their textbooks. In his description of 50 cadaver specimens, Boyden [14] reported one case (2%) of segmental vein 2 (V2) draining into the IPV, which he named the posterior segment of the right upper lung (S3); therefore he actually called the vein V3, not V2, in his textbook) [14]. Similarly, Yamashita [15] stated that the frequency of V2 draining into the IPV was 2.4% (4 cases out of 170 cadaver specimens). The frequency of UVPBI in the IPV group reported in these studies agrees with our data. However, neither author mentioned the drainage pattern into the SPV and the LA, posterior to the bronchus intermedius.
Computed tomography studies of the UVPBI consist of only a few series [911]. In the largest one, Kim and colleagues [9] analyzed nodularity in the posterior wall of the bronchus intermedius on 280 normal CT scans. According to their report, the frequency of UVPBI was 3.6%, whereas that of LVPBI was 1.7%. Thus, the overall prevalence of pulmonary veins posterior to the bronchus intermedius was 5.3%. In addition, with respect to the drainage pattern of the UVPBI, they reported that 30% (7 of 10) drained into the SPV and 70% (3 of 10) drained into the IPV. Jardin and Remy [11] reported that the frequency of the UVPBI in the IPV group was 9.3% (10 cases from 107 CT images of the right lower lobe). In all the reported cases in which the UVPBI was surgically confirmed, the preoperative CT also clearly detected the UVPBI [1, 2, 16].
Venous drainage patterns of the right upper lobe are usually classified as follows according to the degree of presence of a central vein: central vein type (V1 and V2+3), semi-central vein type (V1+2 and V3), or non-central vein type. Of these, the central vein type is most common, with a reported frequency of 78.3% to 88% [15, 17]. The central vein is easily identified by routine CT. If the central vein is present, it is usually located tangentially within the angle formed by the bifurcation of the right upper lobe bronchus into B2 and B3. The CT level of this bifurcation is the key slice for identifying the central vein. In our study, the presence of UVPBI, especially the presence of a large UVPBI with drainage to the SPV, was significantly associated with a reduced frequency of a central vein. These data suggest that some of the UVPBI are the dominant drainage route of the right upper lobe, especially of the posterior segment, and that a venous drainage pattern containing a large UVPBI represents another independent type.
The most probable operative procedure causing UVPBI injury is the dissection of the posterior aspect of the major fissure. Dissection of the subcarinal, right hilar, or interlobar lymph nodes can also cause UVPBI injury. These situations primarily involve right upper or lower lobectomies. Furthermore, because the UVPBI runs just inside the mediastinal visceral pleura, if the pleural space cannot be identified due to adhesions between the visceral and parietal pleurae, special care must be taken when dissecting the adhesion. Recently, video-assisted thoracic surgery lobectomy has been gaining popularity as a potential alternative to conventional thoracotomy for early stage lung cancer [18, 19]. Vascular injury within such minimally invasive approaches would make hemostasis difficult and force the surgeon to convert to a larger thoracotomy. In particular, massive bleeding from an unknown origin could rapidly lead to a critical situation. The UVPBI and some other vessel variations may thus pose a great danger during video-assisted thoracic surgery. In addition, during median sternotomy or an anterior thoracotomy, because the visibility around the UVPBI is poor, careful manipulation is required. In most cases, dividing the UVPBI first may make subsequent surgical maneuvers safer and easier. However, in cases of a large UVPBI in the SPV group, and especially with a limited pulmonary reserve, preserving the UVPBI may be preferable during a right lower lobectomy. We found two of the UVPBI in the V6 group on CT. To our knowledge, this drainage variation has only been reported by Maciejewski [20]. For this group, he emphasized that V6 and V2 must be ligated separately during lobectomy. The importance of the UVPBI during esophageal resection as well as pulmonary resection, has been recognized [16].
Our study has several limitations. First, unlike thin-section CT, it is not always possible to completely discriminate between the upper lobe and the lower lobe on routine computed tomographic images, even if the lung has a complete interlobar fissure [21]. In the present study, we limited the UVPBI strictly to those veins that were apparently derived from the upper lobe. Thus, the true frequency of the UVPBI might actually be higher than our estimation because some of the veins we categorized as LVPBI might actually have been UVPBI. Second, two scan protocols were utilized in our CT examination: 5-mm collimation at 10-mm intervals, or 10-mm collimation at 10-mm intervals. The first of these two protocols might have made it difficult to detect the horizontal component of the UVPBI, especially in the SPV group, because of the 5-mm gap between two contiguous sections. Finally, because we analyzed computed tomographic images only at lung window settings, we could not visualize the exact courses of the UVPBI within the mediastinum. Thus, our SPV group might also include another group in which the UVPBI drains into the LA independently, a drainage course which Spaggiari and colleagues [1] have previously reported. Determination of a more detailed course of the UVPBI within the mediastinum, especially in the SPV group, would require additional contrast-enhanced CT studies.
In conclusion, the UVPBI is not as infrequent as was previously believed. It can be the main drainage route of the right upper lobe. Preoperative identification of this variation is useful for decreasing the incidence of unexpected intraoperative bleeding. Computed tomography is an effective means of identifying the UVPBI and anticipating its course to the LA. A somewhat greater awareness of anatomical variations while interpreting CT studies may make pulmonary resection safer and more anatomically accurate.
| Acknowledgments |
|---|
|
|
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
T. Nakamura, M. Koide, H. Nakamura, and F. Toyoda The common trunk of the left pulmonary vein injured incidentally during lung cancer surgery. Ann. Thorac. Surg., March 1, 2009; 87(3): 954 - 955. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Endo, H. Tsubochi, T. Nakano, and Y. Sohara A dangerous venous variation in thoracoscopic right lower lobectomy. Ann. Thorac. Surg., February 1, 2009; 87(2): e9 - e10. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |