The key to reconciling our observational studies that small aortas pose only a low risk with the IRAD observation of a substantial number of dissections occurring at small sizes lies in recognition of the “at-risk” denominator pool of patients. Our Yale studies present danger rates for patients under observation at our institution with small aortas; indeed, their risk of aortic events, although not zero, is low—too low to justify surgical intervention. For the IRAD patients with dissection, however, these were drawn from the general population at large. Whether the distribution of aortic sizes is normal or paranormal, the number of at-risk patients increases dramatically as one moves toward normal from the largest aortic sizes in the distribution curve (
Fig. 14). In fact, it is likely that there are millions of patients in the U.S. with aortas between 4 and 5 cm. One could certainly cause harm by operating prophylactically on all of them. In fact, if one were to divide the numerator of observed dissections in IRAD by a denominator of millions, the observed yearly percentage rate of dissection in the small sizes would be very small. Such interpretation supports, as IRAD concluded, that we maintain our current surgical intervention criteria.
