Cavum Septi Pellucidi vs Septum Pellucidum?

Warning: Only for the really nerdy (like us) who want to know which term is appropriate and why!

From:

American Journal of Roentgenology: December 2011, Volume 197, Number 6

Proper Latin Terminology for the Cavum Septi Pellucidi

Thomas Winter and Margaret M. Toscano

At about 12 weeks of gestational age, the corpus callosum starts to develop from the lamina terminalis as a fiber bundle that connects the telencephalic hemispheres. Associated with this is the development of the septa pellucida, two paired clear membranes. The space between the septa is one cavity but has two different names. Anterior to the foramina of Monro, it is called the “cavum septi pellucidi (CSP),” whereas posterior to this structure, it is called the “cavum vergae.” Although the entire space is correctly designated as the “CSP et vergae,” in common usage, the entire cavity is often just called the CSP.

The cavum (literally, a hollow space, hole, or cavity) is closed early in childhood in most individuals, and the two septa are fused. Using the Latin singular, the fused membrane is properly referred to as the “septum pellucidum.” This closure of the CSP et vergae begins at approximately 6 months of gestational age and progresses from back to front. By 3–6 months of postnatal age, the CSP is closed in 85% of individuals, although in a minority this cavity may remain open until adulthood.

It helps to think of the Latin as being entirely descriptive. Thus, the cavity or space (cavum) belonging to the clear (pellucid) walls (septa) is denoted as the CSP because the suffix “i” refers to the genitive form. The genitive is related to the English possessive, as in “dog’s bone” or “God’s son,” so cavum septi literally means “the wall’s space.” The suffix “um” is Latin singular, so the septum pellucidum (clear wall) refers to the fused single membrane that is no longer associated with a cavity. The Latin suffix “a” denotes the plural, so it is proper to speak of the septa pellucida when referring to the paired leaflets themselves. However, when referring to the space between the two septa, because this space “belongs” to the septa, the correct term is now the “CSP.”

This confusing terminology has been commented on at least once in AJR in each of the past two decades. Because proficiency in Latin is deemphasized in our educational system, this distinction may need to be reemphasized in coming decades as well. Interested readers are referred to the superb series of articles by Peter Ronai [6] in this journal almost 20 years ago on pitfalls in medical writing; in particular, his “Advice for Latin Lovers” makes for very enjoyable and educational reading.