The lucid interval associated with epidural bleeding: evolving understanding.

The aim of this paper was to elucidate the evolution of our understanding of the term "lucid interval." A number of texts were reviewed to assess their suitability for analysis. The primary requirement was that the text contain detailed descriptions of a series of patients. Details of the clinical course, the findings and timing of surgery, and, when relevant, the time of death and postmortem findings were required. Books written by Henri-François Le Dran, Percival Pott, and James Hill fulfilled these criteria. Surgical findings included the presence and type of fractures, changes in the bone, separation of periosteum, malodorous or purulent material, tense brain, and hematoma. Postmortem findings supplemented and/or complemented the surgical findings. The courses of the patients were then tabulated, and the correlation between different clinical and operative findings was thereby determined. Our understanding of a lucid interval began in the early 18th century with the work of Henri-François Le Dran and Percival Pott in London. They did not, however, demonstrate an interval without symptoms between trauma and deterioration in patients with epidural hematomas (EDHs). The interval they described was longer than usually expected with EDHs and occurred exclusively in patients who had a posttraumatic infection. In 1751, James Hill, from Dumfries, Scotland, described the first hematoma-related lucid interval in a patient with a subdural hematoma. The first case of a lucid interval associated with an EDH was described by John Abernethy. In the 19th century, Jonathan Hutchinson and Walter Jacobson described the interval as it is known today, in cases of EDH. The most recent work on the topic came from studies in Cincinnati and Oslo, where it was demonstrated that bleeding can separate dura mater and that hemorrhage into the epidural space can be shunted out via the veins. This shunting could delay the accumulation of a hematoma and thus the rise in intracranial pressure, which in turn would delay the development of symptoms. The lucid interval as previously conceived was not properly understood by the French school or by Percival Pott and Benjamin Bell, who all described a symptom-free period prior to the development of infection. The first to have a proper understanding of the interval in relation to an EDH was John Abernethy. The modern description and definition of the lucid interval was the work of Hutchinson and Jacobson in the latter half of the 19th century. Understanding of the pathophysiology of the lucid interval has been advanced by the work of Ford and McLaurin in Cincinnati and a group in Oslo, with the demonstration of what it takes to loosen dura and how an arteriovenous shunt slows down for a while the accumulation of an EDH.