If the autopsy represents the true gold standard for the diagnosis of pulmonary embolism, it is not without a degree of tarnish. First, the mechanism of death from pulmonary embolism is not as straightforward as simple mechanical obstruction; other causes such as reflex and humoral mechanisms have also been implicated. Second, emboli may be easily missed if the pulmonary artery and its branches are not opened with care during autopsy . Large emboli obstructing the pulmonary trunk or main pulmonary arteries will not go undetected if these vessels are opened; however, lobar and segmental vessels are often not systematically cut, and emboli in these vessels often escape detection . The frequency of pulmonary embolism in autopsy patients ranges from 52% to 64% when meticulous dissection techniques with microscopic correlation are used. However, the positivity rate may approach 90% when a large number of lung tissue blocks are studied . Third, despite this discussion, it is not always possible to distinguish premortem from postmortem thrombus or even thromboemboli from thrombi formed primarily in small pulmonary arteries, in which primary thrombosis is far more common than small thromboemboli. In addition, Morpurgo and Rustici found in a review of 49 instances of sudden and unexpected death from pulmonary embolism, 10 involved only peripheral and unilateral branches. These findings are especially disconcerting because small peripheral arteries are also the areas that are difficult to image radiographically.
