Anatomy of the minor fissure: evaluation with thin-section CT

Study on Anatomical Variations in Fissures of Lung by CT Scan

Introduction Refinements in the modern computed tomography (CT) imaging techniques have led to anatomical variations in the fissures of lung being diagnosed more frequently. So far, majority of the studies conducted are cadaveric. There is paucity of studies in this aspect based on chest CT images. Hence, we undertook this study to find the anatomical variations in the fissures. Prior detection of anatomical abnormalities is important to reduce postoperative complications in lung resection surgeries.

Materials and Methods This was a cross-sectional study conducted over a period of 2 years. Data were collected from the patients who underwent CT scan thorax. Patients in whom normal anatomy of lung was distorted and cases where both lungs were not visualized completely were excluded from the study. All the CT images were reviewed by a single radiologist. The presence or absence of the normal and accessory pulmonary fissures, as well as the continuity of each fissure, was recorded by the radiologist. Data were compiled and analyzed.

Results The study population consisted of 394 (70.4%) males and 166 (29.6%) females, totaling 560 cases. Fissural variations were detected in 22.9% (n = 128). Also, 17.5% (n = 98) fissural variations were seen in males and 5.4% (n = 30) fissural variations were seen in females. Further, 54.7% (n = 70) of variations were detected in the right lung and 45.3% (n = 58) in the left lung. The most common fissural variation noted was right incomplete oblique fissure with a frequency of 8.4% cases (n = 47). The most common accessory fissure detected was inferior accessory fissure. Total 22 cases were detected in both the lungs, 17 cases in male and 5 in female.

Conclusion Anatomical variations in fissures were found to be more in the right lung than the left lung. Accessory fissures were detected in higher incidence on the right side.

Accessory and Incomplete Lung Fissures: Clinical and Histopathologic Implications

OBJECTIVE

This article reviews the anatomy, histology, and disease processes of pulmonary fissures, with emphasis on clinical implications of accessory and incomplete fissures.

CONCLUSION

Accessory and incomplete pulmonary fissures are often overlooked during routine imaging but can have profound clinical importance. Knowledge of fissure anatomy could improve diagnostic accuracy and inform prognosis for oncologists, interventional pulmonologists, and thoracic surgeons.

Preoperative delineation of pulmonary fissural anatomy at multi-detector computed tomography in children with congenital pulmonary malformations and impact on surgical complications and postoperative course

BACKGROUND

Delineation of the anatomy and integrity of the pulmonary fissures at CT is important because anomalous or incomplete fissures might increase the risk of surgery and of postoperative complications.

OBJECTIVE

To preoperatively evaluate the integrity of the pleural fissures in children with congenital lung malformations and determine whether anomalous fissural anatomy is a risk factor for a more complicated surgery and postoperative course.

MATERIALS AND METHODS

We reviewed preoperative multi-detector CT scans of consecutive children who underwent open or thoracoscopic resection of a congenital pulmonary malformation from 2008 to 2018, to determine the integrity of the fissural anatomy, and compared these findings with the surgical report. We correlated postoperative factors including operating room time, days in hospital and chest tube with the operating room documented fissural integrity.

RESULTS

We saw a significant association between the radiologically determined fissural integrity at CT and the operative findings independently for the right, left and both lungs combined (P<0.001). The sensitivity of CT to determine fissural integrity was 76.9%, specificity 95.2%, positive predictive value 95.2%, negative predictive value 76.9%, and accuracy 85.1%. There was a statistically significant association between size of the pulmonary malformation and the integrity of the fissure(s) (P=0.024). Larger lesions also resulted in a significantly longer hospitalization (P=0.024).

CONCLUSION

Chest CT showed high accuracy for delineating fissural anatomy in children with congenital pulmonary malformations, with a good interobserver correlation. Incomplete lung fissures were found more often in children with larger congenital pulmonary malformations. In addition, larger lesions were associated with longer hospital stays. Therefore, children with incomplete fissures may have a longer postoperative course. Analysis of the fissural anatomy should be included in the CT report.

Volumetric thin-section CT: evaluation of pulmonaryinterlobar fissures

PURPOSE

We aimed to perform an imaging analysis of interlobar fissures and their variations using thin-section computed tomography (CT).

METHODS

Volumetric thin-section CT scanning was performed in 208 subjects. Interlobar fissures were observed on axial images, and reconstructed coronal and sagittal images were observed by multiplanar reformatting (MPR). The vessel distributions were verified by maximal intensity projection (MIP). On the axial images, the interlobar fissures were characterized by lines of hyperattenuation, bands of hyperattenuation, avascular zones, and mixed imaging. The interlobar fissures were divided into seven grades according to the percentage of defects over the entire fissure.

RESULTS

On the axial images, of all interlobar fissures without avascular zones, 70.2% of the right oblique fissures (ROFs) and 94.2% of the left oblique fissures (LOFs) appeared as lines, and 83.2% of the horizontal fissures (HFs) appeared as bands. All of the interlobar fissures appeared as lines on the coronal and sagittal images. Of all cases, 17.8% showed fully complete interlobar fissures for all three fissures. Incomplete fissures included 41.3% of ROFs, 58.2% of HFs, and 45.2% of LOFs. In ROFs and LOFs, discontinuity was most frequently below 20%, while in HFs discontinuity was most frequently 41%-60%. The most common classification of incomplete interlobar fissures was a discontinuous avascular zone.

CONCLUSION

Incomplete interlobar fissures are common variations of interlobar fissures. Techniques including volumetric thin-section CT, MPR, and MIP can assist in the diagnosis of incomplete interlobar fissures.

Visibility and variability of pleural fissures on normal digital chest radiographs of 1,000 healthy adults

PURPOSE

To investigate the visibility and variability of pleural fissures on digital chest radiographs.

METHODS

Posteroanterior digital chest radiographs of 566 males and 434 females were retrospectively reviewed for the frequencies and/or appearances of various pleural fissures.

RESULTS

The right only, left only and bilateral minor fissures were visible in 722 (72.2 %), 1 (0.1 %) and 7 (0.7 %) subjects, respectively. The right minor fissures were visible as more than one line in 219 (30.0 %) subjects, i.e., 2, 3 and 4 lines in 214 (29.3 %), 4 (0.5 %) and 1 (0.1 %), respectively. The 955 visible right minor fissures exhibited variable length (<1/3 of right hemithorax, 17.8 %; 1/3-2/3, 60.1 %; >2/3, 22.1 %), alignment (medial higher 40.9 %; lateral higher 54.2 %; horizontal 4.8 %) and contour (convex upward 68.6 %; convex downward 2.7 %; flat 24.9 %; sigmoid 3.8 %). Superolateral major fissures were visualized in 14.8 % (right only 3.0 %; left only 9.0 %; bilateral 2.8 %), superomedial major fissures in 0.3 % (right 0.1 %; left 0.2 %), vertical fissures in 0.5 % (right 0.2 %; left 0.3 %), inferior accessory fissures in 5.4 % (right 4.8 %; left 0.6 %), right superior accessory fissures in 1.2 % and azygos fissures in 0.2 %.

CONCLUSION

The right minor fissure was most frequently visible and exhibited variable appearances. Other pleural fissures were occasionally seen.

Pulmonary fissure integrity and collateral ventilation in COPD patients

Purpose

To investigate whether the integrity (completeness) of pulmonary fissures affects pulmonary function in patients with chronic obstructive pulmonary disease (COPD).

Materials and Methods

A dataset consisting of 573 CT exams acquired on different subjects was collected from a COPD study. According to the global initiative for chronic obstructive lung disease (GOLD) criteria, these subjects (examinations) were classified into five different subgroups, namely non-COPD (222 subjects), GOLD-I (83 subjects), GOLD-II (141 subjects), GOLD-III (63 subjects), and GOLD-IV (64 subjects), in terms of disease severity. An available computer tool was used to aid in an objective and efficient quantification of fissure integrity. The correlations between fissure integrity, and pulmonary functions (e.g., FEV1, and FEV1/FVC) and COPD severity were assessed using Pearson and Spearman's correlation coefficients, respectively.

Results

For the five sub-groups ranging from non-COPD to GOLD-IV, the average integrities of the right oblique fissure (ROF) were 81.8%, 82.4%, 81.8%, 82.8%, and 80.2%, respectively; the average integrities of the right horizontal fissure (RHF) were 62.6%, 61.8%, 62.1%, 62.2%, and 62.3%, respectively; the average integrities of the left oblique fissure (LOF) were 82.0%, 83.2%, 81.7%, 82.0%, and 78.4%, respectively; and the average integrities of all fissures in the entire lung were 78.0%, 78.6%, 78.1%, 78.5%, and 76.4%, respectively. Their Pearson correlation coefficients with FEV1 and FE1/FVC range from 0.027 to 0.248 with p values larger than 0.05. Their Spearman correlation coefficients with COPD severity except GOLD-IV range from −0.013 to −0.073 with p values larger than 0.08.

Conclusion

There is no significant difference in fissure integrity for patients with different levels of disease severity, suggesting that the development of COPD does not change the completeness of pulmonary fissures and incomplete fissures alone may not contribute to the collateral ventilation.

Identification of pulmonary fissures using a piecewise plane fitting algorithm

We describe an automated computerized scheme to identify pulmonary fissures depicted in chest computed tomography (CT) examinations from a novel perspective. Whereas CT images can be regarded as a cloud of points, the underlying idea is to search for surface-like structures in the three-dimensional (3D) Euclidean space by using an efficient plane fitting algorithm. The proposed plane fitting operation is performed in a number of small spherical lung sub-volumes to detect small planar patches. Using a simple clustering criterion based on their spatial coherence and surface area, the identified planar patches, assumed to represent fissures, are classified into different types of fissures, namely left oblique, right oblique and right horizontal fissures. The performance of the developed scheme was assessed by comparing with a manually created "reference standard" and the results obtained by a previously developed approach on a dataset of 30 lung CT examinations. The experiments show that the average discrepancy is around 1.0mm in comparison with the reference standard, while the corresponding maximum discrepancy is 20.5mm. In addition, 94% of the fissure voxels identified by the computerized scheme are within 3mm of the fissures in the reference standard. As compared to a previously developed approach, we also found that the newly developed scheme had a smaller discrepancy with the standard reference. In efficiency, it takes approximately 8 min to identify the fissures in a chest CT examination on a typical PC. The developed scheme demonstrates a reasonable performance in terms of accuracy, robustness, and computational efficiency.

Computerized assessment of pulmonary fissure integrity using high resolution CT

PURPOSE

Knowledge of pulmonary interlobar fissure integrity is of interest in a number of clinical and investigational applications. The authors developed and tested a high resolution CT based automated computerized scheme for this purpose.

METHODS

The fissure integrity assessment scheme consists of the following steps: (1) Fissure detection, (2) individual fissure identification, (3) fissure type determination, (4) "complete" interlobe surface estimation, and (5) fissure integrity estimation. For evaluation purposes, 50 anonymized chest CT examinations were ascertained and the complete and "incomplete" regions of the fissures of interest were manually marked by two experienced radiologists. After applying the scheme to the same examinations, differences among fissure percent completeness estimates based on the radiologists' manual markings and the automated computerized scheme were computed and compared.

RESULTS

Average differences in estimated fissure percent completeness (integrity) between the results of the computerized scheme and that based on each of the two radiologists' markings were 6.88% +/- 5.86%, 9.57% +/- 7.77%, and 4.19% +/- 5.64% for the right major fissures, the right minor fissures, and the left major fissures, respectively. The differences between results based on radiologists' markings for the same fissures were 4.27% +/- 3.32%, 7.02% +/- 5.54%, and 4.23% +/- 4.93%, respectively. The difference among the three matched measurement sets for each fissure were statistically significant (Friedman's test, p < or = 0.005) but paired comparisons showed that much of the observed difference was related to inter-reader differences rather than reader-computerized scheme differences. Computerized estimates were correlated with each of the radiologist's estimates (Spearman, p < 0.0001).

CONCLUSIONS

While variability between readers-based estimates of fissure integrity was smaller than differences between the computerized scheme and each of the readers, the result reported here are quite encouraging in that the magnitude of these differences were in the same magnitude, demonstrating the feasibility of using a computerized scheme for this purpose.

Correlative anatomy for thoracic inlet; glottis and subglottis; trachea, carina, and main bronchi; lobes, fissures, and segments; hilum and pulmonary vascular system; bronchial arteries and lymphatics

Because it is relatively inexpensive and universally available, standard radiographs of the thorax should still be viewed as the primary screening technique to look at the anatomy of intrathoracic structures and to investigate airway or pulmonary disorders. Modern trained thoracic surgeons must be able to correlate surgical anatomy with what is seen on more advanced imaging techniques, however, such as CT or MRI. More importantly, they must be able to recognize the indications, capabilities, limitations, and pitfalls of these imaging methods.

Lung resection for primary bronchial carcinoma in a patient with complete situs inversus

Complete situs inversus is a rare syndrome with a frequency estimated at 1-2/10,000 births. Situs inversus may go unrecognized until discovery during emergency surgery or investigation of symptoms. We present a case of confirmed adenocarcinoma of the left lung, treated by upper lobectomy. The computed tomography (CT) scan of the thorax showed a mirror-image of the organs and vessels, confirmed by aortography and pneumoangiography. The heart was structurally normal. Abdominal CT scan showed a mirror-image of the abdominal organs. At thoracotomy, the gross appearance of the left lung and the arrangement of the pulmonary vessels and the bronchi corresponded to that normally found on the right side. Preoperative diagnosis of situs inversus in patients undergoing surgical treatment is important for operative technique and prevention of vessel injury. Preoperative angiographic examination is mandatory in patients with situs inversus undergoing lung resection.

Visualization of Normal Pulmonary Fissures on Sagittal Multiplanar Reconstruction MDCT

OBJECTIVE

Delineation of the interlobar fissures on multiplanar reconstruction (MPR) images is useful to assess masses at the fissures for invasion into adjacent lobes. We performed this study to determine the appropriate MDCT protocol to visualize the interlobar fissures on sagittal MPR images.

MATERIALS AND METHODS

For the phantom studies, radiographic film was used to replicate the interlobar fissures. For the clinical studies, we obtained MDCT scans of 130 patients with normal interlobar fissures. Visualization of the interlobar fissures on sagittal MPR was assessed using the following scanning parameters: scan collimations of 0.5, 1, 2, and 3 mm with helical pitches of 1 and 1.5 for the phantom studies; and scan collimations of 0.5, 1, 2, and 3 mm with a helical pitch of 1.5 and a scan collimation of 2 mm with a helical pitch of 1 for the clinical studies.

RESULTS

To visualize fissures as a sharp line, a 0.5- or 1-mm collimation was required for the major fissure and 0.5 mm for the minor fissure in the phantom studies. In the clinical studies, 0.5-mm-collimation MPR images depicted interlobar fissures as a sharp line in all cases. Fissures on MPR images using 1-, 2-, and 3-mm collimations appeared as a sharp line in 77.5-95.0%, 0-43.3%, and 0% of cases, respectively.

CONCLUSION

Volume data obtained using a 1-mm collimation are required to visualize all the interlobar fissures as a sharp line on sagittal MPR images except the minor fissure and superior portion of the right major fissure, for which a 0.5-mm collimation is required.

The morphological features of major and accessory fissures observed in different lung specimens

The current study reports the presence of accessory fissure and anomalies in the major fissure and lobation in both the right and left lungs. The results indicated that out 102 lung specimens observed in the dissection room 37.26% appeared to have fissural or lobation anomalies and 63% of the anomalies were described in the right lung. Fissural anomalies accounted for 28.44% while the lobation anomalies were observed in 8.82% of the specimens. The abnormal fissure that were observed included the left minor fissure 10.78%, incomplete horizontal fissure 7.84%, diaphragmatic fissure 7.84%, right minor fissure 0.98% and azygos fissure 0.98%. Further observation revealed that 5.88% of the right lungs appeared to have two lobes and 2.94% of the left lungs had three lobes. The current study indicates that the right lung is commonly affected with fissural and lobation anomalies and that the left minor fissure is the commonly occurring fissural anomaly. Documentation and familiarization of these anomalies remain to be important for making correct radiological diagnosis and also for proper surgical management of lung pathology.

High Resolution CT Anatomy of the Pulmonary Fissures

RATIONALE AND OBJECTIVES

Pulmonary interlobar fissures are important landmarks for proper identification of normal pulmonary anatomy and evaluation of disease. The purpose of this study was to define the radiologic anatomy of the pulmonary fissures using high resolution computed tomography (HRCT) in a large population.

METHODS

HRCT of the lungs from aortic arch to diaphragm was performed in 622 patients, with a slice thickness of 1 mm and slice interval of 10 mm. Major, minor, and accessory fissures were studied for their orientation and completeness.

RESULTS

Both major fissures were mostly facing laterally in their upper parts (100% and 89% right and left, respectively). The left major fissure faced medially (69%) while the right major fissure faced lateral (60%) in their lower parts. The right major fissure was more often incomplete (48% as compared with 43% on the left, P < 0.05). Minor fissures were convex superiorly with the apex in the anterolateral part of the base of the upper lobe, and were incomplete in 63% of cases. Azygos, inferior accessory, superior accessory, and left minor fissures were also seen in 1.2%, 8.6%, 4.6%, and 6.1% of the cases, respectively.

CONCLUSION

The pulmonary fissures are highly variable and the right major fissure differs considerably from the left. The fissures are often incomplete.

HRCT evaluation of the accessory fissures of the lung

INTRODUCTION

The purpose of this study was to classify the accessory fissures of the lung and to assess their frequency by using high-resolution CT.

METHODS AND PATIENTS

HRCT scans of 115 patients were prospectively reviewed. 1 mm thin sections were obtained at 10 mm intervals with a scan time of 1.9 s. The fissure and its relationship to the segmental bronchovascular structures were then evaluated on transverse sections.

RESULTS

Forty-four accessory fissures were detected in 35 of 115 patients. The most common accessory fissure was the inferior accessory fissure (12%). The second most common accessory fissure was the left minor fissure (8%). The right superior accessory fissure (5%), the accessory fissure between the medial and lateral segments of the right middle lobe (5%), and the accessory fissure between the superior and inferior segments of the lingula (5%) were seen in equal frequencies. Also, intersegmental accessory fissures, namely the fissure between the anterobasal and laterobasal of both the right (1%) and the left (2%) lower lobes were detected. We found only one subsegmental accessory fissure.

DISCUSSION AND CONCLUSION

The inferior accessory fissure and the left minor fissure were the most common accessory fissures in our study.

Variation in major pulmonary fissures: incidence in fetal postmortem examinations and a review of significant extrapulmonary structural abnormalities in sixty cases

A retrospective study of 1513 fetal postmortem examination reports from 1967 to 1996 yielded 35 cases with anomalous major pulmonary fissures (2.3%), to which a further 25 cases were added from fetal postmortem examinations performed between 1929 and 1966. Of 60 cases with anomalous fissures, 43 had an absent right horizontal fissure and 8 had a supernumerary left horizontal fissure; the remaining 9 showed various patterns in which one lung lacked major fissures. Histological examination in 29 cases did not reveal any additional pulmonary abnormality and pulmonary maturity was appropriate for gestational age. Additional malformations were present in 40 cases and these were frequently multiple, the most common being central nervous system, cardiovascular, and genitourinary system defects; notable heart malformations (10 cases); hydrocephalus (5 cases); and cystic renal dysplasia (4 cases). Chromosomal abnormalities were demonstrated in six cases although this figure does not reflect their prevalence, as many cases predate the availability of karyotyping. In seven cases, including three with polysplenia syndrome and one with situs inversus totalis, there was evidence of an underlying abnormality of left-right asymmetry, and in 13 cases there was documented pulmonary hypoplasia.

Septal structure of incomplete interlobar fissures of the lung

RATIONALE AND OBJECTIVES

Some septal structures have been observed in the areas of incomplete interlobar fissures (IIFs) in resected lungs. We describe the anatomy of IIFs with or without the presence of septal structures.

METHODS

Twenty fused areas from 16 autopsy cases were examined histologically. Other septal structures outside the areas of IIFs also were examined.

RESULTS

In 10 of the 20 fused areas, there was a mixture of septal structures with and without defects. In the remaining 10, there were no septal structures. The septal structures consisted of two inner layers from both lobes. Other septal structures examined were the same as ones observed in the IIFs.

CONCLUSION

Linear shadows seen at interlobar fissures and on computed tomography scans do not necessarily depict the presence of complete interlobar fissures. The absence of linear shadows does not necessarily imply the absence of septal structures.

Radiology of the pleural fissures

The pleural fissures, formed by a double layer of visceral pleura, represent extensions of the pleural space between lobes of the lungs. The fissures are frequently an anatomic barrier to the spread of inflammatory or neoplastic disease. Identification of the fissures is important for the accurate localization of lung parenchymal or pleural pathology. The plain radiographic and computed tomographic (CT) imaging of normal and variant fissural anatomy, as well as of some abnormalities that may affect the fissures will be reviewed and illustrated.

Radiological features of asbestos-related visceral pleural changes

The radiological manifestations of asbestos-related visceral pleural changes are described. Generally, visceral pleural reactions follow the mesothelial cells response to various injurious substances, including asbestos, and even saline. The changes are nonspecific. They may occur subsequent to pleural reactions associated with many conditions, which include tuberculosis, viral pleurisy, malignancy and lymphoma, lupus, or rheumatoid-induced effusions, cardiac failure, and pulmonary embolism, among other etiologies. The failure to absorb the fibrinous exudate on the visceral pleural surface can lead to the development of diffuse fibrosis of the serosal surface, interlobar pleural thickening, localized pleural filaments (strands), subpleural wedge, and lenticular-shaped masses, and could be the forerunner of lobular atelectasis (pseudotumor) formation. Some of the features are recognized on posteroanterior chest radiographs and the counterparts corroborated with the use of routine and high-resolution computed tomography studies.