Acute interstitial pneumonia (Pneumonia interstitialis acuta) is a pathological process characterized by primary acute inflammatory involvement of the interstitial tissue of the respiratory divisions and alveolar walls. The disease is accompanied by secondary exudate formation within the lumens of bronchioles and alveolar spaces. In scientific and medical literature, this nosology is also found under the synonymous terms "acute pneumonitis" or "atypical pneumonia".
Primary involvementInterstitium of the respiratory divisions and alveolar wall
Nature of effusionSecondary appearance of exudate in alveoli and bronchioles
Pathology courseProlonged persistence of the pathogen in the body
Pleural involvementFrequent development of fibrinous pleuritis
Definition, Terminology, and Nosological Status
Acute interstitial pneumonia (also known as acute pneumonitis) occupies a special place among respiratory system pathologies. This process has the following terminological and clinicomorphological features:
Nosological forms: The disease can occur as a primary independent nosology or act as a secondary pathological process.
Literature designations: In scientific publications and manuals, this pathology is often called "atypical pneumonia". This name is explained by the fact that the disease differs significantly from classical pneumonias in its clinical presentation and applied therapeutic methods.
Features of the course: The pathogenetic profile of this condition is characterized by the prolonged presence (persistence) of the pathogen in the human body.
Macroscopic Appearance of Lung Pathology
Post-mortem examination and visual inspection of the organ reveal a complex of characteristic changes in the lung tissue and adjacent structures:
Bronchopneumonic pattern: A picture of bronchopneumonia developing with involvement of several lung lobes at once is observed.
Similarity to lobar involvement: In a certain proportion of cases, the macroscopic appearance of the organ has noticeable similarities to lobar pneumonia in the stage of gray hepatization.
Pleural involvement: A reactive process—fibrinous pleuritis—is recorded on the pleural leaves.
Microscopic Features and Histopathology
Histological examination of sections of the affected lung tissue determines the following key microscopic changes:
Vascular and tissue disorders: Pronounced hemorrhagic edema of the respiratory divisions is revealed.
Cellular infiltrate: Massive infiltration by cellular elements—macrophages and polymorphonuclear leukocytes—is traced in the alveolar septa.
Primary and secondary nature of changes: Primary acute inflammation is localized in the interalveolar septa and the interstitium of the respiratory divisions, while the formation of exudate inside the lumens of alveoli and bronchioles is secondary in nature.
Summary Characteristics of Pneumonia Forms
Terminological variant | Morphological essence | Morphogenetic features --- | --- | --- Acute interstitial pneumonia | Primary inflammation of the alveolar wall and interstitium | Secondary exudate in alveoli and bronchioles Acute pneumonitis | Synonym for interstitial pneumonia | Prolonged persistence of the infectious agent in the body Atypical pneumonia | Designation due to clinical picture and treatment | Resembles gray hepatization, yields fibrinous pleuritis
Mnemonic
INTERSTITIUM — Infiltration by macrophages and leukocytes, Native alveolar wall origin, Torpid course with pathogen persistence, Exudate secondary in bronchioles, Resulting in fibrinous pleuritis.
Frequently asked questions
What microorganisms are the most frequent pathogens of acute interstitial pneumonia?
Etiological factors of acute interstitial pneumonia include viruses, mycoplasmas, chlamydia, legionella, rickettsia, the agent of psittacosis, fungi, and pneumocystis. Viral variants can be caused by influenza viruses, parainfluenza viruses, and adenoviruses; the H1N1 strain poses a particular danger among influenza viruses. In some cases, the etiology remains undetermined, as in Hamman-Rich disease. A viral-bacterial nature of the disease is possible.
What are the typical morphological outcomes of acute interstitial pneumonia?
Morphological outcomes include the formation of moderately pronounced pulmonary interstitial fibrosis in the late stage and septoalveolar sclerosis with the progression of productive inflammation. Nonspecific interstitial pneumonia has a relatively favorable course and a fairly high survival rate. Hamman-Rich disease represents acute interstitial pneumonia of unknown etiology with a fatal outcome within 2–4 months from acute cor pulmonale and heart failure.
What pulmonary and extrapulmonary complications can develop in acute interstitial pneumonia?
Complications of usual interstitial pneumonia include the development of cor pulmonale and progressive cardiopulmonary failure.
Which lung structure is primarily affected in acute interstitial pneumonia?
Primary acute inflammation is localized in the interstitium of the respiratory divisions of the lung and directly in the alveolar walls. The formation of inflammatory exudate inside the lumens of alveoli and bronchioles occurs secondarily.
Why is acute interstitial pneumonia called "atypical"?
The term "atypical pneumonia" is used in the literature due to the characteristic features of the clinical picture of the disease and the use of specific treatment methods that differ from the therapy of classical pneumonias.
What are the key macroscopic manifestations of the pathology?
Macroscopically, bronchopneumonia involving multiple lobes is revealed, in some cases resembling lobar pneumonia in the stage of gray hepatization, as well as fibrinous inflammation of the pleura (fibrinous pleuritis).
Which cells infiltrate the alveolar septa on microscopy?
Histological microscopic examination reveals hemorrhagic edema, and infiltration by macrophages and polymorphonuclear leukocytes is determined in the alveolar septa.
Go deeper
Secondary nature of acute interstitial pneumonia in concomitant pathologies
The stage of gray hepatization in lobar pneumonia and its morphological similarity to interstitial pneumonia
Mechanisms of long-term persistence of pathogens in lung tissue
Features of therapy in the atypical course of acute pneumonitis