right upper lobar bronchus anomalous origin at tracheal lower third level [17, 18].

•\ Lower accessory ssure: It was described by Nelson and is located in the lower lobe, separating segment 6 from the rest of the lobe (basal pyramid). When this occurs, the lung portion associated with this segment is called Fowler’s lobule.

Pleural Vascularization

Arterial andVenous

Irrigation [19, 20]

Parietal pleura arterial circulation comes from the aortic artery systemic territory, through small arterioles from intercostal arteries that irrigate the costal pleura and the diaphragmatic pleura most peripheral part; by internal thoracic and pericardial-phrenic arteries branches that supply the mediastinal pleura, and by cranial phrenic arteries branches that supply the diaphragmatic pleura central part.

However, the visceral pleura arterial blood supply comes primarily from the pulmonary or functional circulation, via pulmonary capillaries. This pulmonary territory peripheral circulation circuit receives systemic pulmonary communications from bronchial artery branches, through Leford’s precapillary anastomosis or Von Hayeck’s post-capillary anastomosis (Figs. 29.12, 29.13 and 29.14).

Parietal Pleura Lymphatic Drainage

The lymphatic system begins with tiny stomata, 8–10 μm in diameter, that are scattered on the pleural endocavitary surface, and that communicate in a dense lymphatic collectors network, equipped with endoluminal valves, (with negative pressures inside), draining into submesothelial lymphatic lacunae or cisterns. These lacunae have a collagen bers layer and mesothelial cells on the pleural side, and endothelial cells on the lacuna side. They can remove up to 20 times the volume of fuid formed under normal conditions, approximately up to 0.2 mL/kg/h.

v.br

a.br

A.P.

V.P.

Br. Seg.

Fig. 29.13  Subpleural pulmonary microcirculation. A.P.: peripheral pulmonary artery V.P.: peripheral pulmonary vein, a.br.: subsegmentary bronchial artery, v.br.: subsegmentary bronchial vein, Br.Seg.: subsegmentary bronchus

Following the general outline of the body, the parietal pleura lymphatic vessels form a dense subpleural network that drains most of the fuid, accompanying the intercostal, internal thoracic, pericardiophrenic, and superior phrenic veins along its course.

At the costal pleura, lymph collects in the intercostal lymph nodes on the posterior side, and by the internal thoracic vein lymph nodes on the anterior side.

The diaphragmatic pleura drains the lymph towards ganglion chains located in the mediastinum, and in the vicinity of the celiac trunk [21].

Visceral Pleura Lymphatic Drainage

Visceral pleura lymphatic circulation is more complex, draining through two systems:

\(a)\ A super cial subpleural network that circulates on the lung surface directly towards the pulmonary hilum.