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| ORIGINAL ARTICLE |
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| Year : 2022 | Volume
: 11
| Issue : 4 | Page : 204-210 |
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Morphometric study of fissures of lung with its clinical implications
Sabita Singh1, Jeneeta Baa1, Arpita Soy1, Mamata Sar2, Dibya Prabha Bara1
1 Assistant Professor, Department of Anatomy, V.S.S. Institute of Medical Science and Research, Burla, Odisha, India
2 Professor and HOD, Department of Anatomy, V.S.S. Institute of Medical Science and Research, Burla, Odisha, India
| Date of Submission | 14-Sep-2022 |
| Date of Decision | 09-Oct-2022 |
| Date of Acceptance | 13-Oct-2022 |
| Date of Web Publication | 29-Oct-2022 |
Correspondence Address:
Dibya Prabha Bara
Assistant Professor, MD Anatomy, Department of anatomy, V.S.S. Institute of Medical Science and Research, Burla, Odisha
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/NJCA.NJCA_157_22
Background: Complete or incomplete fissures divide the lung into lobes. Fissures can also be absent in the lung. Quantitative assessment of the completeness of fissures can be helpful for surgeons and radiologists during invasive procedures related to the lung. Hence, the present study was undertaken to record the extent of completeness of fissures, contour of the fissural surface of lobes, and accessory fissures. Methodology: The present study was done on 78 (right-40 and left-38) formalin-fixed random lung specimens obtained from adult cadavers. Results: Majority of oblique oblique fissures were incomplete (left-60.5% and right-60%). The absence of fissures was mainly seen in horizontal fissures (25%). Quantitative assessment for the degree of pulmonary fissure completeness showed that G0 and G3 were found more in the right oblique fissure (ROF) and horizontal fissure, G1 and G2 more in the left and ROF, respectively. Fissural surface of lower lobe was concave in the upper part and convex in the lower part, whereas fissural surface of middle lobe was convex in the majority of cases. Accessory fissures were found in 21.8%. Azygos fissure was present in two right lungs. A strong correlation was found between the depth of oblique fissure and the thickness of left lung. Conclusion: High frequency of incomplete fissures was found. Accessory fissures were commonly observed in the right lung. A wide range of variations in the completeness of fissures was noticed between the present and previous studies. Hence, surgeons and radiologists should be alert of these variations for surgical planning and interpretation of radiological images.
Keywords: Accessory fissure, horizontal fissure, lung fissure, oblique fissure, pulmonary fissure completeness
How to cite this article:
Singh S, Baa J, Soy A, Sar M, Bara DP. Morphometric study of fissures of lung with its clinical implications. Natl J Clin Anat 2022;11:204-10 |
How to cite this URL:
Singh S, Baa J, Soy A, Sar M, Bara DP. Morphometric study of fissures of lung with its clinical implications. Natl J Clin Anat [serial online] 2022 [cited 2023 Mar 29];11:204-10. Available from: http://www.njca.info/text.asp?2022/11/4/204/359878 |
| Introduction | |  |
The lungs are paired respiratory organs located in the thorax. The right lung is divided into upper, middle, and lower lobes by oblique and horizontal fissures. The left lung is divided into upper and lower lobes by an oblique fissure. The oblique fissure extends from the costal to the mediastinal surfaces separating the lower lobe from the middle and superior lobe except at the hilum. Horizontal fissures extend from oblique fissure at the mid-axillary line up to the anterior border at the fourth costal cartilage separating the middle lobe from the upper lobe.[1] Uniform expansion of the lung during respiration is possible due to fissures which help in air intake in greater amounts.[2]
Lung fissures can be complete, incomplete, or absent. Complete fissures separate the lobes wholly but not at the hilum, whereas parenchymal fusion between the lobes is present in incomplete fissures. There is a varied extent of parenchymal fusion leading to the different degrees of completeness of fissures and fusion of lobes in the case of incomplete fissures.[3] Knowledge of variations in fissure configuration is mandatory for locating the lobes and bronchopulmonary segment.[4] During video-assisted thoracoscopic lobectomy, the degree of pulmonary fissure completeness has to be considered by thoracic surgeons.[5]
The upper and lower part of the fissural surface of the lower lobe of both lungs is usually concave and convex, respectively. The fissural surface of the middle lobe of the right lung can be concave, convex, or flat. Knowledge of the contour of the fissural surface can help to explain the radiographic appearance of interlobar fluid and prevent misinterpretation.[6]
Accessory fissures may also present in the lungs which usually show the junctions of bronchopulmonary segments. Accessory fissures are of three types – superior accessory fissure (SAF), inferior accessory fissure (IAF), or left minor fissure (LMF). The accessory fissures can be present as a notch or incomplete fissure or even as a complete fissure. It is visible as a thin white line, which appears similar to an oblique or horizontal fissure radiologically.[7] It might be not detected on computed tomography (CT) scans due to incompleteness of fissure.[8]
Most of the anatomical study on the fissures of the lung was focused on its type rather on its morphometry. The extent of depth of the oblique fissure is more useful clinically than its length during thoracic surgery for surgery of the pulmonary artery at the depth of the oblique fissure.[9] Hence, this study on the classical lung fissures was conducted to record the extent of completeness, contour of lobes along the fissures as well as accessory fissures. This study is also an attempt to find the relation between circumference and depth with the thickness of the lung.
| Materials and Methods | | |
The present study was done on 78 (right-40 and left-38) cadaveric lungs obtained from the dissection hall and museum of the Department of Anatomy V. S. S. Institute of Medical Science and Research, Burla. Ethical committee approval for this study was taken, and the ethical clearance number is 005-2022/I-F-O/13 (17-05-2022).
The lungs having pathological lesions, marks of previous surgery, fibrosis, and having any cuts during the removal of lungs were excluded from the study. The morphometric parameters of fissures were recorded and tabulated.
Fissures were categorized based on the classification proposed by Craig and Walker as Type I, Type II, Type III, and Type IV.[3] In this study, the Type III had been further subdivided as Type IIIa-Visceral cleft evident for a part of the fissure but reaching up to the hilum and Type IIIb-Visceral cleft evident for a part of the fissure with parenchymal fusion.
The degree of completeness of the fissure was calculated as the depth of fissure/thickness of the lung in percentage. Thus, the completeness of fissures was quantified and also graded (G0–G4) as per classification by Li et al.[9]
- Grade 0 (G0) – complete fissure which separate the lobe completely.
- Grade 1 (G1) – more than 70% completeness of the interlober fissure
- Grade 2 (G2) – 30%–70% completeness of the interlobar fissure
- Grade 3 (G3) – absent fissure or less than 30% completeness of the interlobar fissure.
The depth of fissures was recorded by introducing a digital vernier caliper perpendicular to the surface at the midpoint of the fissure on the costal surface. Thickness was taken as the distance between the mediastinal (center of the hilum) and the costal surface (midpoint of an oblique fissure at costal surface). Circumference was also recorded to find out if any relations exist between circumference and depth with the thickness of the lung. Circumference was measured starting from the anterior border of the hilum at its maximum width, crossing the midpoint of the oblique fissure on the costal surface, and again ending at the hilum. Fissural surfaces of the lower lobe were divided into the upper part and lower part taking its midpoint on the costal surface of the lungs.
Statistical analysis
Data which were in numbers was calculated and recorded as a minimum and maximum values. Furthermore, mean values, standard deviations, and percentages were calculated. Statistical correlations were made between (i) the circumference and thickness of the lung and (ii) the depth of fissure and thickness of the lung by calculating the Coefficient of determination (R2) in a scatter plot. The strength of the association was measured by calculating Pearson's correlation coefficient.
| Results | | |
Out of 38 left lungs, left oblique fissure (LOF) was complete in 12 (31.6%), incomplete in 23 (60.5%), and absent in 3 (7.9%) lungs. Out of 40 right lungs, the right oblique fissure (ROF) was complete in 16 (40%) and incomplete in 24 (60%). The horizontal fissure (HF) was complete in 11 (27.5%), incomplete in 47.5 (19%), and absent in 10 (25%) lungs. These fissures were classified as per Crag and Walker classification [Table 1], [Table 2], [Table 3] and [Figure 1], [Figure 2], [Figure 3]. The completeness of fissures was quantified as per Shuangjiang Li et al.[9] and summarized in [Figure 4]. | Figure 1: Left lungs showing different types of oblique fissures seen from costal surface; (a) type I, (b) type II, (c) type IIIa, (d) type IIIb, (e) type IV
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 | Figure 2: Right lungs showing different types of oblique fissures seen from costal surface; (a) type I, (b) type II, (c) type IIIa, (d) type IIIb
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 | Figure 3: Right lungs showing different types of horizontal fissures seen from costal surface; (a) type I, (b) type II, (c) type IIIa, (d) type IIIb, (e) type IV
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 | Figure 4: Bar graph showing degree of oblique and horizontal pulmonary fissures Completeness. LO: Left oblique fissure, RO: Right Oblique fissure, RT: Right Transverse fissure (Horizontal Fissure)
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Accessory fissures were found in 17 lungs (21.8%) [right lung-IAF-9 (22.5%), left lung-IAF-2 (5.3%), and LMF-6 (15.8%)] [Figure 5]. SAF was not observed in any lungs. Azygos fissure was present in two right lungs [Figure 5]f. Besides this, four right lungs have accessory fissures in locations other than for SAF, IAF, and LMF. | Figure 5: Lungs showing accessory fissures (white arrow); (a) IAF in left lung, (b) IAF in right lung, (c) LMF in left lung, (d and e) accessory fissures in other locations, (f) Azygos fissure (yellow arrow) and accessory fissure (white arrow). IAF: Inferior accessory fissure, LMF: Left minor fissure
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Various fissural surfaces of the oblique and horizontal fissures of lungs are described in [Table 1],[Table 2],[Table 3] and shown in [Figure 3]a, [Figure 3]b, [Figure 3]c, [Figure 3]d, [Figure 3]e, [Figure 6]a, [Figure 6]b, and [Figure 7]a, [Figure 7]b, [Figure 7]c, [Figure 7]d, [Figure 7]e. | Figure 6: Left lungs showing fissural surface (upper-lower part) of lower lobe; (a) concave convex, (b) flat flat; Right lungs showing fissural surface of middle lobe, (c) concave, (d) convex, (e) flat
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 | Figure 7: Right lungs showing fissural surface (upper-lower part) of lower lobe; (a) concave convex, (b) convex convex, (c) convex concave, (d) convex flat, (e) flat flat
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Mean with standard deviations and range of the length, depth of fissures and circumference, and thickness of lung were calculated [Table 4]. A linear relation between the depth of the oblique fissure and the thickness of the lung was found in the left side and was strongly correlated (Pearson's correlation coefficient-0.43, P < 0.01) [Figure 8]. Such a relation was not seen in the right side. No correlation was found between circumference and thickness in any of the lungs. | Figure 8: Scatter plot showing statistical relation between thickness of left lung and depth of left oblique fissure
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 | Table 4: Dimensions of lung fissures, circumference and thickness of lung
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| Discussion | | |
Repeated branching of secondary bronchi results in the development of lungs. Bronchopulmonary segments are formed by repeated branching for several generations. Lung develops from the fusion of bronchopulmonary buds during development except at fissures by which lobes and fissures are formed.[10] Abnormal fusion of the buds results in variations of lobes and fissures.[11] In the present study, the incomplete fissure was found in greater frequency (LOF-60.5% and ROF-60%) than the complete fissure (LOF-31.6% and ROF-40%) [Table 1], [Table 2], and [Figure 1], [Figure 2]. Various authors also reported incomplete fissure in the majority of cases; incomplete LOF by Frija et al.(77%) and Glazer et al.(52%);[10],[12] Incomplete ROF by Glazer 1991 (64%), Dutta et al.(61.5\4%), Jacob and Pillay (50%), and Magadum et al.(60%)[12],[13],[14],[15]; Incomplete right horizontal fissure by Medlar (62.3%), Meenakshi et al.(63.3%), Bergman et al.(67%), and Prakash et al.(57.1%).[4],[16],[17],[18] Dutta et al. found a greater frequency of incomplete oblique fissures on the right side. It might be due to early fusion of the fissures during the embryonic period resulting in lung parenchymal fusion along the bottom of the fissure.[13] LOF was absent in three (7.9%) cases but none of the right lungs had absent oblique fissures. However, the absent oblique fissure was reported by Medlar in 7.3%, 4.8% and by Prakash et al. by 10.7%, 7.1% of left and right lungs, respectively.[16],[18]
Parenchymal fusion occurs between lung lobes gives passage to the spread of disease and collateral air drift.[19] In incomplete fissures, an atypical type of pleural effusion can be resulted by lung collapse in endobronchial lesions.[4] Many authors reported absent horizontal fissures except Mamatha et al.[20] In our study, the absent horizontal fissure was found in 25% [Figure 3]e. Lymphatic drainage of the lung passes from the pleura toward the lung. Change in depth and course of oblique fissures also results in a change in visceral pleura course which can alter the arrangement of lymphatics of the lungs.[21] Knowledge about incomplete fissures is essential for lobar resection planning due to the possibility of air leaks in lobar fusion.[19]
As per Crag and Walker classification, Kc et al. reported that the majority of LOFs were of Type III (51.9%) in contrast to other studies which showed a higher frequency of Type I.[22] In this study, also maximum LOF was of Type III (52.6%). Literature shows that Type I ROFs and horizontal fissures were more in number except in our case, where both of these fissures were of Type III. Type IV fissure is commonly present in horizontal fissures. This Type IV ROFs was seen in the present study and Nene et al.[Table 5].[24] | Table 5: Comparison of pulmonary fissure completeness (Craig and Walker's classification) by various author
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Li et al. reported different degrees of pulmonary fissure completeness in a retrospective analysis of 563 patients undergoing video-assisted thoracoscopic lobectomy for nonsmall-cell lung cancer. Findings of their study in terms of the extent of pulmonary fissure completeness were similar to the present study where G0 and G3 were found more in ROF and HF. However, in the present study, we found G1 more in the LOF and G2 in the ROF [Figure 4]. The morbidity rate increased significantly in patients with incomplete pulmonary fissures as compared to complete pulmonary fissures. Increased frequency of pneumonia, pleural effusion, prolonged air leak, and subcutaneous emphysema were found in the case of incomplete pulmonary fissures. Duration of hospital stay and pleural drainage were also increased.[9]
In a study of 100 fixed (left-50 and right-50) inflated lungs by Raasch et al., the upper part fissural surface of the lower lobe was usually concave (left-88% and right-52%) and the lower part was convex (left-82% and right-55.8%).[6] In the present study also, similar findings were observed, in which the upper part was mostly concave and the lower part convex [Figure 6]a, [Figure 6]b, [Figure 6]c, [Figure 6]d, [Figure 6]e and [Figure 7]a. The maximum fissural surface of the middle lobe was found convex (66%) and few cases were concave 8% by Raasch et al. but none was flat.[6] In the present study, the majority of the fissural surface of the middle lobe was convex (65%), but in 5% of cases, the surface was flat [Figure 6]d and [Figure 6]e.
Dutta et al. reported that the length of oblique fissures was 27.32 ± 7.29 cm (11 cm–40.5 cm) in the right lung and 30.15 ± 6.26 cm (20.5 cm–43 cm) in the left lung, whereas Bhimai Devi et al. reported the length of the oblique fissure was of range 7 cm–28 cm in the right lung and 13 cm–28 cm.[13],[23] In the present study, the length of oblique fissures was 30.42 ± 11.7 cm (20 cm–44 cm) in the right lung and 31.2 ± 5.2 cm (19 cm–43 cm) in the left lung. In addition, the length transverse fissure was also measured (6.7 ± 5.2 cm; 3 cm–20 cm) [Table 4]. This showed that the length of fissures showed a wide variation.
In a study by Dutta et al., the depth of the oblique fissure was maximum as 5.73 ± 1.41 cm.[13] In the present study, the depth of the oblique fissure was similar (LOF-4.6 ± 1.9 and ROF-5.6 ± 1.5) [Table 4]. The thickness of the lung was strongly correlated with the depth of the oblique fissure in the left side [Figure 8]. However, these relations were weak in the right side. Hence, further studies are needed to establish these relations.
Accessory fissure varies in depth and is lined by visceral pleura.[7] Nonobliteration of spaces which should be usually obliterated results in the formation of the accessory fissure.[4] It can present as a notch or complete fissures. Accessory fissures previously found were of three types – SAF, IAF, and LMF. SAF and IAF separate apical and medial basal segments from the rest of the segment of the lower lobe, respectively. Lingula separated from the left upper lobe by LMF. Accessory fissures are usually missed during CT scans or can be misinterpreted. Linear atelectasis areas, walls of bullae, or pleural scars are commonly confused with accessory fissures. Accessory fissures may alter the lung collapse which creates difficulty in the diagnosis in the endobronchial lesion. Accessory fissures can also prevent the spread of infection.[7] Nene et al. and Magadum et al. reported IAF in 14%, 5% of the right lung, 24%, 8% left lung, and LMF in 26%, and 7.5%, respectively.[15],[24] According to Godwin and Tarver, an accessory fissure can also present in locations other than that of SAF, IAF, and LMF.[7] In the present study also, accessory fissures were found in other locations [Figure 5]d and [Figure 5]e.
The medial part of the upper lobe can be incompletely separated into medial and lateral parts by azygos fissures which can present vertically or obliquely of varying depth. Azygos veins are present in the bottom of this fissure which is suspended by mesentery formed by mediastinal pleura. The medial part of the upper lobe is called the lobe of azygos vein which is usually supplied by apical bronchus.[1] A case of azygos fissure was reported out of 27 right lungs studied by Kc et al.[22] Two right lungs had azygos fissures out of 40 right lungs in our study [Figure 5]f.
Limitation
This study was done in 78 cadaveric lungs. Hence, it needs to be done in more cadavers by further researchers.
| Conclusion | | |
High frequency of incompleteness of both oblique and transverse fissures was found in the present study. The absence of fissures was mostly seen in horizontal fissures. Accessory fissures were mostly incomplete with higher frequency in the right lung. Quantitative assessment of the completeness of fissures can be more helpful for surgeons and radiologists during invasive procedures related to the lung. The present study and their comparison with previous studies showed wide variations in the completeness of fissures. It shows that the development of fissures can be affected genetically or the environment may influence it. A strong correlation was found between the depth of LOF and the thickness of the left lung. Prior anatomical knowledge is essential for surgeons for prior effective surgical planning and for radiologists for accurate interpretation.
Acknowledgments
The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase humankind's overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude.[28]
We would like to thank Dr. Aliva Patra, Assistant Professor, Community Medicine, VIMSAR, Burla, for her contribution for statistical analysis. Furthermore, we would like to thank the staff of the dissection hall for their technical assistance for specimen collection.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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