P1130009

Two kinds of corpora lutca can be distinguished during thc dicstrus iii marcs: Compact corpora lutca and hemorrhagic corpora lutca (Pibrson and GlNTHBR 1985 a). A solid corpus luteuni dcvelops in about half of all marcs after ovulation whilc in the othcr half a corpus hcmorrhagicum forms. No functional differcnce ap-pears to exist between the two typcs of corpora lutca (Townson et al. 1989). Both, progesterone concentra-tions and cyclic events, are the same in marcs with a corpus luteum or a corpus hemorrhagicum. Knowledge of the typical appearance of a corpus luteum is, however, important for its correct ultrasonic identificatioń.

Solid corpora lutea have a homogenous echogenicity and structure across their entire cross sectional surface when viewed by ultrasonography (Fig. 1.26). The entire compact corpus luteum seems to consist of tissue of equal echogenicity throughout. They retain the same echogenicity for the duration of diestrus.

The second form of corpora lutea, the corpus hemorrhagicum, consists of two distinct zones of differing

uppearanee: A hyperechoic pcriphcral edge and a cen-trał, less echoic eore area (Mg. 1.27). In the lattcr the cchocs vary from hypoechoic to almost uncchoic and not infrcquenlly thcy form trabecular, web 1'ike patiem*. Thesc two zones of corpora hemorrhagica result from the echoic pcriphcral zonę of luteinizcd tissuc and the hypoechoic central zonę of the blood ciot, rc*peetiveły (Fig. 1.28). The blood ciot reflects ultrasound less strongly than the lutcinized wali and is somctimes traversed by a nctwork of fibrin.

After ovulation, the entire cross sections of almost all hemorrhagic corpora lutea are echoic (PfERSON and Gintjibk 1985 a). Only after a few days can the hypoechoic central area be distinguished from the morę echoic peripheral area. On the third day of the cyclc of-ten less than half of the cross sectional surface area of a corpus luteum consists of echoic luteinizcd tissue (Fig. 1.27). As the cycle progresses the echoic areas enlarge; by Day 9 of the cycle they make up about 70 %, by the end of the cycle usually 100 %, of the corpus luteum.