A thin line in the right lower lung field: which fissure ?

Clinical History

An adult male patient underwent a plain chest x-ray for a routine work check up, which revealed the presence of a thin ondulating line in the medial aspect of the lower right pulmonary field, in the paracardiac region.

Imaging Findings

Plain chest x-ray radiograph perfomed as a routine work check up, in an otherawise healthy male patient.

Discussion

In this case (figures 1 and 2) we discuss the importance and prevalence of the fissures of the lower right lung region, and whether the thin line seen in this case (Figure 1-2) is an inferior accessory fissure, an accessory fissure of the right middle lobe, or a sagittally oriented anterior minor fissure. The minor fissure of the right lung separates the middle lobe from the upper lobe, and its anterior aspect of the minor fissure tends to be more caudal than the posterior aspect, thus causing the appearance of two parallel lines in the frontal chest x-ray examination (1).   It is well known that the inferior accessory fissure is the most commonly seen accessory fissure, as reported from autopsy studies, plain x-ray radiographs of the chest (2), CT of the thorax (3) and HRCT of the lungs (5), its frequency on HRCT being reported at 20% in the right lung (4). The inferior accessory fissure, which separates the mediobasal segment of the lower lobe from the remainder of the lower lobe, originates from the posterior aspect of the major fissure and runs from superomedial to inferolateral (3) occasionally extending supero-medially and even reaching the hilum, thus in our opinion, with a fairly different course than on this case.   The accessory fissure of the middle lobe, seen in 2% of HRCT (4), is an accessory fissure between the lateral and medial segment of the middle lobe. Whether the fissure seen in this case is really an accessory fissure of the middle lobe could be determined with absolute certainty only with a CT examination; we consider this hypothesis unlikely though, because the course of the accessory fissure of the middle lobe is more lateral, as seen on other published cases (5,6). It appears as a vertical line, usually straight or slightly ondulated, arising at the costal surface of the middle lobe and running towards the hilum from an anterolateral position to a posteromedial one (4).   The third possibility, which we consider the possible right answer for this fissure, is a sagittally oriented anterior minor fissure, which has been reported firstly by Gross in 1988 and confirmed by CT by the same author (7). The importance of considering the different possible answers we have exposed lies in the fact that in each of them lies the potential of a wrong diagnosis. It might be taken for a scarring or atelectasic line thus representing the outcome of a previous disease condition, or a misplaced major or minor fissure, thus implying a volume loss. The most serious diagnostic mistakes might arise when there is a pathologic condition in the adjacent lung parenchyma, as right upper lobe disease (in the case of the sagittal anterior minor fissure) may simulate a mediastinal mass, or disease in the medial segment of the middle lobe (should it be mistaken for an accessory middle lobe fissure), or even disease affecting the lower lobe, if it were mistaken for an inferior accessory fissure.

Differential Diagnosis List

Final Diagnosis

Sagittaly oriented anetrior minor fissure.

URL:	https://www.eurorad.org/case/5202
DOI:	10.1594/EURORAD/CASE.5202
ISSN:	1563-4086