Asynclitic Presentation

ASYNCLITIC PRESENTATION, or asynclitism. Asynclitic presentation is defined as the abnormal engagement of the fetal head during labor. Engagement is understood to denote the relationship of the sagittal suture to the pelvic inlet, more accurately, to its two main reference points—the sacral promontory and the symphysis. Normal engagement of the head is considered to be when the sagittal suture passes through the transverse diameter of the pelvic inlet, with approximately equal distance from the promontory and the pubis (axial or synclitic engagement). Any other engagement of the head should be considered abnormal asynclitic presentation. There are several types of asynclitic presentations, among which the anterior and posterior parietal presentations have the greatest practical importance.-1. Anterior parietal presentation, or anterior asynclitism, Naegele asynclitism (engagement with the anterior parietal bone). In this type of presentation, the anterior parietal bone, located near the symphysis, is the first to enter the pelvic inlet, causing the sagittal suture to pass closer to the sacral promontory. Depending on the greater or lesser distance of the sagittal suture from the promontory, three degrees of anterior asynclitism can be distinguished: a) Naegele, or anterior parietal inclination—the first mild degree of asynclitism, when we have only slight flexion of the head toward the posterior shoulder; b) Naegele engagement—more pronounced engagement of the anterior parietal bone: the sagittal surve sharply and for a prolonged time approaches the promontory; c) so-called anterior auricular engagement, in which the wedging of the anterior parietal bone is so pronounced that the anterior ear is clearly palpable at the symphysis during internal examination. Naegele asynclitism, especially its first degree, as a transient phenomenon, can occur—not so rarely—in normal labor (physiological anterior asynclitism). This is usually observed in multiparous women with a pendulous abdomen (venter propendens). According to Gauss, pronounced anterior parietal engagement is relatively frequently observed (approximately in 50% of cases) in twins, during engagement of the head of the first twin. Such abnormal engagement usually disappears in the further course of labor. The most common cause of anterior asynclitism is a narrow pelvis, mainly a flat pelvis. Naegele asynclitism in a flat pelvis constitutes one of the essential features of the so-called period of head configuration (see Pelvis). Depending on the degree of pelvic narrowing, we can also have the aforementioned anterior auricular engagement. Anterior parietal engagement is also not infrequently observed in large infants with normal pelvic dimensions. In most cases, Naegele engagement in a flat pelvis does not prevent the completion of labor by natural forces. More rarely, labor must be completed with the application of forceps.-2. Posterior parietal presentation, posterior asynclitism, Litzmann asynclitism (engagement with the posterior parietal bone). In contrast to anterior engagement, in posterior asynclitism the sagittal suture is closer to the symphysis (in front of the midline of the pelvic inlet). Thus, the posterior parietal bone, located near the sacrum, is the first to enter the cavity of the small pelvis. Corresponding to Litzmann asynclitism, we will also have three degrees in posterior parietal presentation: a) Litzmann inclination (the sagittal suture passes 1½-2 cm in front of the midline of the pelvis), b) Litzmann engagement (the suture passes immediately behind the upper edge of the pubic bone) and c) posterior auricular engagement (the posterior ear can be palpated above or even below the promontory during internal examination). Litzmann inclination can be observed—though not so frequently (0.58% according to Baisch)—in primiparas, especially with firm abdominal walls that can delay the anterior parietal bone at the symphysis (physiological posterior asynclitism). With further deeper descent of the head, such inclination corrects itself, and the posterior bone catches up with the anterior one. To facilitate such correction, some recommend placing the patient on the side where the fetal brow is located. True Litzmann engagement and posterior auricular engagement usually occur in flat pelvises and especially frequently—with their most unfavorable form—in flat generally contracted pelvises. In this case, posterior parietal engagement should from the very beginning be regarded as a serious complication of the labor process—especially if the posterior ear is palpated on examination. Labor under such conditions cannot complete spontaneously, so active therapy must be instituted from the very beginning. Manual maneuvers recommended by some obstetricians for correcting posterior parietal presentation [e.g., the manual maneuver of the kegel ball, "Kegelkugelhandgriff" by Liepmann] do not achieve the goal. If the fetus remains mobile, labor must be completed by internal version to a breech presentation; with fixed posterior parietal presentation, it is necessary to resort to perforation, replacing it, under appropriate conditions and circumstances, with cesarean section.-Besides anterior and posterior asynclitism, there are still some other, from the point of view of practical medicine, less significant and less important abnormal engagements of the head. These include:-3. Rederer asynclitism, wedge-shaped engagement of the head with possibly deep position of the small anterior fontanelle. Due to excessive flexion of the head, the small anterior fontanelle descends so low that even with a high head it is located almost in the middle of the pelvic aperture. Rederer asynclitism constitutes a characteristic feature of the mechanism of labor in a generally uniformly contracted pelvis (see Pelvis). No special therapy is required.-4. Solayres asynclitism, the sagittal suture engages diagonally in the pelvis, i.e., in one of its oblique diameters. Occurs in obliquely contracted pelvises.-5. Engagement of the head in the anteroposterior diameter of the pelvis, high direct engagement of the head ("Hoher Geradestand" of the Germans)—a rare anomaly of head engagement; in such asynclitism, the head at the inlet immediately enters the anteroposterior diameter. M. Malinovsky.