Page 520 - Textbook of Pathology, 6th Edition

504 Pulmonary hamartomas are of 2 types: chondromatous and PLEURA
leiomyomatous.
Chondromatous hamartoma is more common and NORMAL STRUCTURE
usually asymptomatic. It forms a solitary, spherical mass, Visceral pleura covers the lungs and extends into the fissures
2-5 cm in diameter, usually at the periphery of the lung. while the parietal pleura limits the mediastinum and covers
Typically, it shows nodules of cartilage associated with the dome of the diaphragm and inner aspect of the chest wall.
fibrous and adipose tissue admixed with bronchial The two layers between them enclose pleural cavity which
epithelium.
contains less than 15 ml of clear serous fluid.
Leiomyomatous hamartoma has a prominent smooth
muscle component and bronchiolar structures. They are Microscopically, both the pleural layers are lined by a single
frequently multiple, 1-2 mm in diameter and are more layer of flattened mesothelial cells facing each other.
commonly located near the pleura. Underneath the lining cells is a thin layer of connective tissue.
Diseases affecting the pleura are nearly always secondary
to some other underlying disease. Broadly, they fall into
METASTATIC LUNG TUMOURS
inflammations, non-inflammatory pleural effusions,
Secondary tumours of the lungs are more common than the pneumothorax, and tumours.
primary pulmonary tumours. Metastases from carcinomas
as well as sarcomas arising from anywhere in the body may INFLAMMATIONS
spread to the lung by haematogenous or lymphatic routes, Inflammatory involvement of the pleura is commonly termed
or by direct extension. Blood-borne metastases are the most pleuritis or pleurisy. Depending upon the character of resultant
common since emboli of tumour cells from any malignant exudate, it can be divided into serous, fibrinous and
tumour entering the systemic venous circulation are likely serofibrinous, suppurative or empyema, and haemorrhagic
to be lodged in the lungs. Metastases are most common in pleuritis.
the peripheral part of the lung forming single or multiple,
discrete nodular lesions which appear radiologically as 1. SEROUS, FIBRINOUS AND SEROFIBRINOUS
‘cannon-ball secondaries’ (Fig. 17.40). Less frequently, the PLEURITIS. Acute inflammation of the pleural sac (acute
metastatic growth is confined to peribronchiolar and pleuritis) can result in serous, serofibrinous and fibrinous
perivascular locations which is due to spread via lymphatics. exudate. Most of the causes of such pleuritis are infective in
SECTION III
Most common sources of metastases in the lungs are: origin, particularly within the lungs, such as tuberculosis,
carcinomas of the bowel, breast, thyroid, kidney, pancreas, pneumonias, pulmonary infarcts, lung abscess and
lung (ipsilateral or contralateral) and liver. Other tumours bronchiectasis. Other causes include a few collagen diseases
which frequently metastasise to the lungs are osteogenic (e.g. rheumatoid arthritis and disseminated lupus
sarcoma, neuroblastoma, Wilms’ tumour, melanoma, erythematosus), uraemia, metastatic involvement of the
lymphomas and leukaemias. pleura, irradiation of lung tumours and diffuse systemic
infections (e.g. typhoid fever, tularaemia, blastomycosis and
coccidioidomycosis).
Pleurisy causes pain in the chest on breathing and a
friction rub is audible on auscultation. In most patients, the
exudate is minimal and is resorbed resulting in resolution.
Repeated attacks of pleurisy may result in organisation
Systemic Pathology
leading to fibrous adhesions and obliteration of the pleural
cavity.

2. SUPPURATIVE PLEURITIS (EMPYEMA THORACIS).
Bacterial or mycotic infection of the pleural cavity that
converts a serofibrinous effusion into purulent exudate is
termed suppurative pleuritis or empyema thoracis. The most
common cause is direct spread of pyogenic infection from
the lung. Other causes are direct extension from subdia-
phragmatic abscess or liver abscess and penetrating injuries
to the chest wall. Occasionally, the spread may occur by
haematogenous or lymphatic routes.
In empyema, the exudate is yellow-green, creamy pus
that accumulates in large volumes. Empyema is eventually
replaced by granulation tissue and fibrous tissue. In time,
tough fibrocollagenic adhesions develop which obliterate the
Figure 17.40 Metastatic deposits in the lung. Large parts of the cavity, and with passage of years, calcification may occur.
lung parenchyma are replaced by multiple, variable-sized, circumscribed The effect of these is serious respiratory difficulty due to
nodular masses which are grey-white in colour. Some of these show
areas of haemorrhage and necrosis. inadequate pulmonary expansion.