And now the singular has been found, coined seven years before Borgmann constructed it:
The name illustrates an important feature of this disease, "subendolymphatic hyperplastic proliferation." . . . It was Dr. Frank's feeling that this was a subendolymphatic proliferation of the endothelium lining these spaces . . . .
--American Journal of Obstetrics and Gynecology (1957) 73: 1070
Borgmann's coinage is no longer purely madeupical (but the singular form still hasn't been spotted outside the laboratory):
"The increased prevalence of salpingitis due to N. gonorrhoeae at the time of menses has fostered the contention that the loss of mucosal integrity and the rich supply of subendolymphatics are important variables in transforming occult glandular infection into clinically recognized disease."
--Gilles R. G. Monif and David A. Baker, 2008, Infectious Diseases in Obstetrics and Gynecology, p. 451