Bronchial obstruction, particularly with bronchogenic carcinoma obstructing a bronchus or bronchiole. Impaired drainage, distal atelectasis, and aspiration of blood and tumor fragments all contribute to the development of abscesses. An abscess also may form within an excavated necrotic portion of a tumor.
Septic embolism, from infective endocarditis of the right side of the heart.
In addition, lung abscesses may result from hematogenous spread of bacteria in disseminated pyogenic infection. This occurs most characteristically in staphylococcal bacteremia and often results in multiple lung abscesses.
Anaerobic bacteria are present in almost all lung abscesses, and they are the exclusive isolates in one-third to two-thirds of cases. The most frequently encountered anaerobes are commensals normally found in the oral cavity, principally species of Prevotella, Fusobacterium, Bacteroides, Peptostreptococcus, and microaerophilic streptococci.
MORPHOLOGYAbscessesrangeindiameterfromafewmillimeterstolargecavities5to6cmacross.Thelocalizationandnumberofabscessesdependontheirmodeofdevelopment.Pulmonaryabscessesresultingfromaspirationofinfectivematerialaremore common on the right side (withitsmoreverticalairways)thanontheleft,andmostaresingle.Ontherightside,theytendtooccurintheposteriorsegmentoftheupperlobeandintheapicalsegmentsofthelowerlobe,becausetheselocationsreflecttheprobablecourseofaspiratedmaterialwhenthepatientisrecumbent.Abscessesthatdevelopinthecourseofpneumoniaorbronchiectasiscommonlyaremultiple,basal,anddiffuselyscattered.Septicemboliandabscessesarisingfromhematogenousseedingarecommonlymultipleandmayaffectanyregionofthelungs.
Asthefocusofsuppurationenlarges,italmostinevitablyrupturesintoairways.Thus,thecontainedexudatemaybepartiallydrained,producinganair-fluidlevelonradiographicexamination.Occasionally,abscessesruptureintothepleuralcavityandproducebronchopleuralfistulas,theconsequenceofwhichispneumothorax orempyema. Othercomplicationsarisefromembolizationofsepticmaterialtothebrain,givingrisetomeningitisorbrainabscess.Onhistologicexamination,asexpectedwithanyabscess,thesuppurativefocusissurroundedbyvariableamountsoffibrousscarringandmononuclearinfiltration(lymphocytes,plasmacells,macrophages),dependingonthechronicityofthelesion.
The manifestations of a lung abscess are much like those of bronchiectasis and include a prominent cough that usually yields copious amounts of foul-smelling, purulent, or sanguineous sputum; occasionally, hemoptysis occurs. Spiking fever and malaise are common. Clubbing of the fingers, weight loss, and anemia may all occur. Abscesses occur in 10% to 15% of patients with bronchogenic carcinoma; thus, when a lung abscess is suspected in an older adult, underlying carcinoma must be considered. Secondary amyloidosis (Chapter 5) may develop in chronic cases. Treatment includes antibiotic therapy and, if needed, surgical drainage. Overall, the mortality rate is in the range of 10%.
Chronic pneumonia most often is a localized lesion in an immunocompetent individual, with or without regional lymph node involvement. There is typically granulomatous inflammation, which may be due to bacteria (e.g.,