A Study on Morphological Variations of Fissures and Lobes of Human Lungs with its Clinical Signicance

Background Fissures of lungs facilitate the movement of lobes which helps in expansion of lungs during breathing. The ssures may be complete, incomplete or absent. Sometime the accessory ssures may also present. Awareness of variations is essential during segmental resections as well as during radiological interpretation of lungs. Hence, the present study was aimed to study the morphological variations in ssures and lobes. Material and Methods This study consisted of sixty nine human lungs with irrespective of sex which were available in the department of anatomy of various medical colleges. All lung specimens were carefully observed and recorded for the presence of any variations in ssures and lobes. Results The present study revealed that the absence of horizontal ssure was observed in 7.89% of right lungs, while no specimen showed absence of oblique ssure on both lungs. Incomplete oblique ssure was recorded 35.48% of left lungs and 28.95% of right lungs. In addition, 22.58% of right lungs and 23.68% of left lungs showed presence of accessory ssure and lobes. The incomplete and absence of horizontal ssures were more common abnormalities observed in this study. The accessory ssures were more common in lower lobe of right lungs whereas they were more common in upper lobe of left lungs.


Introduction
A pair of lung is important organs of respiratory system, located in the thoracic cavity. There are presence of two ssures (oblique and horizontal) on the right lung which divide it into upper, middle and lower lobes. There is only one oblique ssure on left lung which divides it into upper and lower lobes [1]. The ssures may be complete when they are attached to each other at the hilum of lung or they may be incomplete when there is parenchymal tissue present between the lobes. The ssures allow the movement of lobes which also provide distension and uniform expansion of lung [2]. A study suggested that ssures are important landmarks for proper identication of normal morphology and diagnosis of disease [3]. In many clinical cases, localization of segment is essential. Presence of accessory ssures has to be considered for the pre-operative planning and strategy for pulmonary lobectomy and surgical resections involving individual segment [4]. The accessory ssures frequently fail to be detected on computed tomography scans, because of their incompleteness [5]. The knowledge of anatomical variations of the lobes and ssures of lung is important for identifying broncho-pulmonary segments and surgical resections involving individual segment [6]. Hence the present study was aimed to study variations in ssures and lobes of lung with their clinical importance which may help the clinicians during their clinical practices.

Materials and Methods
The cross-sectional and observational study was conducted on 69 formalin xed human lungs (38 right and 31 left) with unknown sex. The sample size was calculated by using G-power formula with condence level 95% and standard error 0.05. Lung specimens were collected from the department of anatomy, Kathmandu University School of Medical Sciences, Dhulikhel, Kathmandu Medical College, Duwakot and Nepal Medical College, Attarkhel during the period of April 2017-December 2017. All specimens were carefully observed and recorded for the presence of any variations such as complete or incomplete oblique and horizontal ssures, absence of ssure, presence of accessory ssure or lobe. A good physical condition or without any damage of lungs were included in the study. The lungs having pathological lesions, marks of previous surgery, damaged during removal with gross abnormalities were excluded from the study. The ethical approval for the study was taken prior to the study.

Right lungs
Out of 38 lungs, only 6 (15.79%) lungs were found anatomically normal with complete both oblique and horizontal ssures as shown in table 1. The right lung showed the oblique ssure was complete in 27 (71.05%) specimens as shown in gure 1 and incomplete in 11 (28.95%) specimens as illustrated in gure 2. Absence of oblique ssure was not recorded. The horizontal ssure was found complete in 11 (28.95%) as shown in gure 1, incomplete in 24 (63.16%) as shown in gure 3 and absent in 3 (7.89%) specimens as shown in gure 4. The presence of accessory ssures and lobes were also recorded in 9 (23.68%) specimens as shown in table 2. Out of these, 2 (5.26%) specimens had accessory ssures in upper lobe as shown in gure 1, 1 (2.08%) specimen had accessory ssure in middle lobe as shown in gure 6, 4 (10.53%) had accessory ssure in lower lobe as shown in gure 4 and 5; and 1 (2.08%) specimen had accessory ssure in diaphragmatic surface as shown in gure 6. Four lobes were also recorded in 1(2.08%) specimen as shown in gure 7.

Left lungs
Out of 31 lungs, it was found normal in 14 (45.16%) specimens as shown in table 1. The oblique ssure was found complete in 20 (64.52%) specimens as shown in gure 9 and incomplete in 11 (35.48%) specimens as shown in gure 8. As shown in table 2, 2 (6.45%) specimens showed accessory ssure in upper lobe as shown in gure 9. Accessory lobe was found in 3 (9.68%) specimens as shown in gure 10, incomplete two lobes were recorded in 1 (3.23%) specimen as shown in gure 11 and incomplete three lobes were also recorded in 1 (3.23%) specimen as shown in gure 12.

Discussion
The lungs are developed from the respiratory diverticulum (lung bud), an outgrowth from the ventral wall of the foregut. First the right and left principal bronchi (bronchial bud) are developed which divides into three secondary bronchial buds on right side and two on left side. Later they develop bronchopulmonary segments [7]. The spaces between the individual bronchopulmonary segments are obliterated except along the line of division of principle bronchi where the deep complete ssures remain dividing the right lung into three lobes and left lung into two lobes.
Fissures are obliquely and horizontally placed in right lungs; and only obliquely placed in left lungs [8].
The lungs are made up of bronchopulmonary segments which form lobes and they are separated from each other by ssures. Each segment has its own tertiary or segmental bronchus [1]. In case of any disease of lungs, initially it would be conned to its own bronchopulmonary segment and then extend to its lobe [9]. The defective development of lung brings about the variations which are incomplete ssure, absence of ssures; and presence of accessory ssures and lobes [2]. Incomplete ssure or absence of ssures could be due to obliteration of ssures either partially or completely. Accessory ssure would be the result of nonobliteration of spaces which are normally obliterated [9]. Due to monopodial branching of principal bronchi, the accessory bronchi and lobes are seen in lungs [10].

Right lungs
In the present study, the oblique ssure was complete in 71.05% and horizontal ssure was complete in 28.95%. It seemed that the variation on completeness occurred frequently on horizontal ssure of right lungs than oblique ssure in a population. The similar ndings were also reported by Thapa and Desai in which they found the incidence of complete oblique ssure in 70% and complete horizontal ssure in 30% [11]. Similarly, Dhanalakshmi et al noticed the incidence of complete oblique ssure in 68% and complete horizontal ssure was in 30% [12]. The knowledge of ssure may signify for identication of lesion within the lungs.
In the present study, oblique ssure was incomplete in 28.95% of specimens which is also supported by studies in which 30% [11] and 30.43% [13] were reported. While, Nene et al (6%) and Tallapaneni (6.66%) revealed lesser incidence of this ssure [4,14] and in contrast Prakash et al (39.30%) found higher incidence of this ssure [15]. Meenakshi et al reported 63.30% [16] of incomplete horizontal ssure which is in accordance with the present study. In contrast, a study was done by Jacob and Pillay who reported 83.4% of this ssure [5] which is higher than the present study. While the researchers also reported very low incidence (8%) of this ssure [4]. Horizontal ssure was absent in 7.89% of specimens in the present study which is also supported by a study conducted by Prakash et al who found 7.10% [15]. In contrast, this ssure was absent in 45.20% [17] which is higher than the present study. While George et al recorded 3.07% [18] which is lower than the present study. But a study was done by Mamatha et al who could not nd any lung with absence of this ssure [19].
In the present study, the accessory ssures and lobes were recorded in 23.68% of specimens. Among them, majority of these ssures were found in lower lobe (10.53%), followed by upper lobe (5.26%), middle lobe (2.08%) and diaphragmatic surface (2.08%). Similarly studies have also reported 4.34% of these ssures in upper lobe [13]. Nene et al [4] revealed 14% of accessory ssures in lower lobe which is almost similar with the ndings (13.16%) of present study. However, KC et al recorded in 21.73% [13]. Few studies did not report any accessory ssures in lower lobe [15,16]. The right lungs usually present three lobes which are separated from each other by oblique and horizontal ssures. In the present study, it was found that 7.89% specimens had only two lobes due to absent or obliteration of horizontal ssure. Specimens with four lobes were also recorded in 2.08% due to presence of accessory ssures. Unver et al have reported the incidence of single lobe in 0.95%, two lobes in 1.90%, three lobes in 95.23% and four lobes in 1.90% [20].

Left lungs
In the present study, complete oblique ssure was recorded in 64.52% of specimens. Similarly, Thapa and Desai; and Dhanalakshmi et al reported the incidence of this ssure in 60% [11] and 62% [12] respectively. In a study, this ssure was found in 73.33% [14] which is higher than the present study.
In the present study, 35.48% of incomplete oblique ssure was obtained. Similar studies were conducted by Mamatha et al and Prakash et al; and they reported 35% [19] and 35.70% [15] respectively. The authors had also reported 46.60% [16] which is higher than the present study. While an author concluded very low (10.60%) [17]. In this study, absence of oblique ssure was not recorded in left lungs. Similarly absence of this ssure was also not reported by few authors [11]. Whereas Mamatha et al recorded in 5% [19] and Prakash et al found in 10.70% [15].
In the present study, accessory ssures were only observed in upper lobe (6.45%) which is in accordance with a study [15]. In the present study, an accessory lobe was found in 9.68%, incomplete two lobes were recorded in 3.23% and incomplete three lobes were also recorded in 3.23% specimens. Whereas variations in lobe were also reported in a study in which the incidence of single lobe in 0.95%, two lobes in 98.10% and three lobes in 0.95% were recorded [20].
The information on presence of accessory ssures would be helpful for medical personnel to differentiate anatomical and pathological changes. An accessory ssure prevents infection to spread and gives good interpretation for differentiating among atelectasis or consolidation [21]. Radiologically an accessory ssure is often mistaken as a lesion [22].

Conclusion
In the present study, the incomplete and absence of horizontal ssures were found more common variations. The accessory ssures were more common in lower lobe of right lungs and upper lobe of left lungs. The accurate knowledge of variations in ssures and lobes of lungs in a particular population might help the radiologist and clinician to make appropriate diagnosis. It might help the surgeon while performing segmental resection of lung.