Bronchoscopy and bronchography revealed a very rare abnormality in the embryonal anatomy of the right bronchial tree in a 54-year-old woman with cough. There was a proximal migration of the apical branch of the right upper bronchus toward the trachea and a distal migration of the two other branches toward the middle lobe bronchus. The proximal migration was accompanied by a narrowing of the trachea. This case is considered an extremely rare embryonal variation in the development of the right bronchial tree.
During the embryonal formation of the bronchial tree, nature carries out her work with a degree of fantasy and a great element of variation. Atwell has suggested that in approximately 10 percent of the patients in whom he carried out bronchography, there were some departures from what might be considered the normal anatomy of the bronchial tree. They are mostly discrete forms of premature or late branching of segmental or subsegmental bronchial branches, or of transpositions in the proximal or distal directions of bronchial segments or subsegments. In only approximately three cases per thousand are superfluous bronchi found and an accessory lung is extremely rare.
The most usual congenital abnormality of the bronchial tree on the right side is the tracheal bronchus. This is normally present in pigs and in ruminants such as cows and sheep, but it is also formed in man in the embryonal stages. However, it is normally completely reabsorbed during the first week of extrauterine life. The right tracheal bronchus, sometimes described as the lobus porcinus or "pig lobe," exists either as an original superfluous bronchus or as a proximal migration of the apical branch of the right upper lobe.[2,4,5] The right upper lobe seems generally to be the place of predilection for congenital anomalies of the bronchial tree.
We describe here a patient with a curious anatomic variant in the distribution of the bronchial branches on the right side in which one segmental branch, probably the posterior one, migrated from the upper lobe toward the trachea and the other two bronchi migrated distally toward the main lower lobe bronchus where they fused together, so that no real right upper lobe could be developed.
On April 16, 1991, a 54-year-old housewife, mother of a healthy 24-year-old daughter, consulted us because ever since an episode of respiratory infection in December 1990, she had continually been short of breath and had had a nonproductive cough. She wheezed and had the feeling that there was something partially blocking the trachea.
Moreover, she had complaints of breathlessness on the slightest exertion and was hyperreactive to cigarette smoke, perfumes, and cold air.
Her history did not reveal any particular diseases and she had not suffered from asthma or hay fever. She was known to have agenesis of the right kidney.
Physical examination showed a woman with a slightly prolonged expiratory phase, but otherwise no abnormalities could be elicited.
The chest radiograph showed no abnormalities but the Mantoux reation was positive.
Laboratory investigations revealed no abnormal results, although allergy tests on the skin showed a weak positive reaction to pollen of spring tree blossom.
Lung function tests disclosed the following results: vital capacity (VC), 2,740 ml (94 percent of predicted value); total lung capacity (TLC), 4,220 ml (87 percent of the predicted value); residual volume, 35 percent of TLC; and [FEV.sub.1], 1,770 ml (73 percent of predicted value). The reversibility was 12 percent after 0.2 mg of formoterol in the form of an aerosol. Dco (single breath) was 86 percent of the predicted value. A nonspecific bronchial PC20 histamine threshold of 3.5 mg/ml was found (slightly lower than normal). The aspect of the volume-flow curve was not one of a high obstruction.
Because of the feeling of obstruction in the chest, bronchoscopy was carried out and showed an unusual bronchial exit on the right side of the trachea at approximately the 10-o'clock position at the level of the lowest third. Beyond this exit, the trachea was narrowed over a distance of approximately 3 cm. Slightly proximal of the apical branch of the right lower lobe bronchus, there was a rather large extrabronchial branch that should have been the right middle lobe bronchus. There were no other bronchial exits and no middle lobe bronchus could be found at all. The anatomy of the right lower lobe appeared to be normal and the left bronchial tree showed no abnormalities. A bronchogram was made on the right side and this confirmed a number of remarkable congenital abnormalities (Fig 1):
(1) There was a tracheal bronchus originating at the level of the lowest third of the trachea (in contrast to the usual findings of a tracheal bronchus that is either lateral or, more usually, anterially placed). The present abnormal exit was posterially placed at approximately the 10-o'clock position. This tracheal bronchus formed a sharp carina with the trachea, pointing in the first instance backwards and downwards. It diminished rapidly to half of the original diameter before setting off posteriorly, and then splitting further into a number of subsegmental bronchi supplying the posterior upper part of the chest.
(2) After the exit of the tracheal bronchus, the trachea showed a narrowing to approximately two thirds of its original diameter over a stretch of 3 to 4 cm.
(3) No actual upper lobe bronchus was found and no trace of this could be observed at the usual place.
(4) The middle lobe bronchus, which had an impressively large diameter, departed higher than usual, namely approximately 1 cm proximal to the departure of the apical bronchus of the right lower lobe. In its distal path it split after approximately 3/4 cm and via a collective channel sent two branches off that filled up the space in the chest normally occupied by the apical and anterior segments of the right upper lobe. Distal to this collective exit, the diameter of the middle lobe bronchus became normal and the distribution within the lateral and medial middle lobe branches was completely normal. The bronchi of the right lower lobe were entirely normal.
Because of what was seen at bronchoscopy and considering what can be observed even better in the right bronchogram, one can derive an impression of what embryologic misadventures this woman suffered, together with the right-sided renal agenesis. We know that the respiratory organs have their origin in the tubus cephalicus, more precisely in the conductus pulmonalis, and we know also that the bronchial tree develops by means of a process of repeated budding.
The siting of the two main bronchi becomes differential in the course of the fourth embryonal week. Five to 8 days, later the buds develop and form the lobar and then segmental bronchi. In this patient, something went wrong during the primary stage of the formation of the trachea: when this was two thirds formed it would seem that the developmental bud of the right lower lobe became active, in particular when laying down the posterior segmental branch. There was a mistaken attempt to develop the main carina at too early an embryonal stage. The bud for the development of the posterior branch of the right upper lobe lateroposteriorly to the trachea found that it had not laid down a right main bronchus but had formed a segmental branch. It then corrected its diameter and its direction of growth (no longer downwards at an angle of 45[degree], but posteriorly), bifurcated, and split its subsegmental branches off.
After the branching, the trachea grew further with the diameter of a main bronchus but then recovered its normal caliber and then developed further by forming a bud for the left bronchial tree and the remainder of the right side of the carina (thus without the bud of the posterior side of the right upper lobe). The left bronchial tree developed completely normally. The right main bronchus developed but nevertheless missed the embryonal stimulus to form an upper lobe (probably because the energy was already used up by the outgrowth of the trachea).
Somewhat prematurely, long before the right lower lobe and especially before its apical branch had developed, the right middle lobe bud advanced to produce a wider than normal diameter whereby the two remaining segmental branches of the upper lobe suddenly separated from the host bronchus and went their own ways after a short period of fusion. The lateral and medial middle lobe developed further quite normally.
In this patient, the tracheal bronchus is therefore almost certainly not a true "lobus porcinus." It did not leave laterally but posteriorly, it filled up the posterior space instead of the apical space, and moreover it formed a sharp carina with the trachea. The collective departure of the apical and anterior bronchial branches of the right upper lobe in the presence of a separate posterior branch is a relatively common variation, and Nagaishi found if in 24 percent of subjects. The most frequently noted variant is, however, the collective departure of the bronchi for all three upper lobe segments and this can be noted in 40 percent of cases. The bronchial distribution within the right upper lobe in our patient was not so unusual. The simultaneous occurrence of a proximal migration of the posterior branch and a distal migration of the anterior and apical branches, however, has to be considered as extremely rare.
 Atwell SW. Major anomalies of the tracheo-bronchial tree. Dis Chest 1967; 52:611-15
 Kertes I, Radics J, Serenyi P. Les anomalies de la division de l'arbre bronchique. Bronches 1960; 10:577-94
 Maesen FPV, Santana B, Lamers J, van den Brekel B. A supernumerary bronchus of the right upper lobe. Eur Respir J 1983; 64:473-76
 Boucher H, Souquet R, Roumagoux J, Petitjean R. Les anomalies dans la distribution et la morphologie des bronches. Presse Med 1960; 31:1213-21
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 Nagaishi C. Functional anatomy and histology of the lung Baltimore: University Park Press
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