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Commentary |
1 Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710.
Received June 27, 2005; accepted after revision July 10, 2005.
Each month the American Journal of Roentgenology will republish
online one of the 100 most-cited articles from its first century. A
corresponding commentary in the print journal by a contemporary radiologist
will provide a current perspective. For a full list of these articles see page
3 of the January 2006 issue of
AJR or
www.ajronline.org.
Keywords: cancer • neuroimaging • radiography
In "The Volume of the Sella Turcica," DiChiro and Nelson set out to provide a systematic approach to providing details of the size of the sella turcica based on radiographic measurements [1]. The authors do indeed succeed in defining a method for relatively accurately measuring sellar volume. However, it is more interesting to look at the article as a means for understanding the problems faced by radiologists before the development of cross-sectional imaging than it is to consider the influence the article had on subsequent neuroradiologic discovery. Recognizing the obstacles that DiChiro and Nelson faced leads to an appreciation of the accomplishments featured in this article.
In an era before the use of CT, DiChiro and Nelson addressed the issue of how to derive a 3D volume of the sella from measurements obtained via conventional radiography. Knowing the volume of the normal sella would be important for determining the likelihood that a pituitary mass was present and for diagnosing other conditions affecting the sella. In the article, DiChiro and Nelson reviewed previous techniques for deriving sellar volume and provided their own solution based on meticulous measurements as well as comparison with measurements made in cadavers without pituitary gland disease.
One difficulty is that several different measuring techniques for the volume of the sella based on measurements made on radiographs are possible, depending, for example, on whether one measured the width of the sella on a posteroanterior projection or a submentovertex projection. The problem was summarized by Sir Godfrey Hounsfield, who is credited with the development of CT 10 years after DiChiro and Nelson published their article on sellar volume. In his Nobel Prize acceptance speech, Hounsfield noted, "it is impossible to display within the framework of a 2-dimensional X-ray picture all the information contained in the 3-dimensional scene under view. Objects situated in depth, i.e., in the third dimension, superimpose, causing confusion to the viewer" [2]. The development of cross-sectional imaging techniques such as CT and MRI provided a means to move beyond the limitations of volumetric measurement imposed by radiography.
As DiChiro and Nelson pointed out, other fundamental issues exist when measurements of sellar volume are used to infer changes within the pituitary gland. For instance, the sella contains more than solely the pituitary gland, such as a perihypophyseal venous plexus; connective tissue; and, on occasion, benign abnormal structures such as an arachnoid cyst. Therefore, the pituitary gland can be expanded by the presence of a mass lesion at the expense of other sellar contents without changing the volume of the sella. As DiChiro and Nelson stated, "considerable enlargement of the pituitary may be unobservable roentgenologically." In other cases, the pituitary gland occupies only a small amount of the sella even though the sella is normal or large—the empty sella syndrome. In essence, in the absence of cross-sectional techniques that could directly visualize the contents of the sella, DiChiro and Nelson had to use the size of the container (i.e., the sella) to infer the size of its contents. The two are often, but not always, correlated.
The article on sellar volume by DiChiro and Nelson foreshadowed the use of volumetric measurements in radiology, which has seen substantial growth in the past few years. Increasingly, radiologists are required to provide quantitative measurements of various entities, such as tumors and aneurysms. Such measurements require a high degree of reproducibility. It is safe to say that if DiChiro and Nelson were to submit their manuscript today, reviewers and readers would wish to know the intra- and interobserver variability of their sellar measurements. However, it would not be fair to judge this manuscript by current standards. The authors were ahead of their time in the meticulous assessment of the volume of the sella turcica and the application of their measurements to various disease processes.
In summary, this article used advanced methods to attempt to deal with a relatively common problem faced by radiologists and provided guidelines for estimating the relative likelihood that a pituitary mass was present in any given patient. DiChiro and Nelson provided important information that was based on careful evaluation of a large number of patients. This article deserves merit in any review of important articles in the history of radiology.
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  J. M. Provenzale Morphology Predicts Oncology: A Commentary on Vezina and Sutton's Article, "Prolactin-Secreting Pituitary Microadenomas: Roentgenologic Diagnosis" Am. J. Roentgenol., January 1, 2007; 188(1): 9 - 10. [Full Text] [PDF]
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