The relationship of myometrial histopathology (metropathy) to myometrial dysfunction and clinical manifestations

Abnormal Uterine Involution May Lead to Atony and Postpartum Hemorrhage: A Hypothesis, With Review of the Evidence

“…Our experience confirms the observation of Shahid et al (Figure 1(b)); however, our studies of developing uteri and nonpregnant hysterectomies for bleeding suggest that this outer wall edema and vascular ectasia (outer pressure effects) is secondary to increased intramural pressure, as first suggested by Farrer-Brown and co-workers in the 1970s. 5,10,16,18,20,27 We believe this pressure-induced outer wall edema has nothing to do with myometrial involution. However, increased intramural pressure in the growing myometrium of early pregnancy—associated with the palpable bump in the abdomen that is a sign of early pregnancy—may lead to venous obstruction, with endometrial vascular ectasia, fibrin thrombi, and stromal breakdown, causing early pregnancy bleeding.…”

“…In the era of Rutherford and Hertig, the theory of metropathy (myometrial histopathology) dominated thinking about “menorrhagia myopathica,” that is, abnormal bleeding due to myometrial pathology. 5,17,18 Although unproven, this theory was supported in 1966, when a morphometric study of myometrium by Schwalm and Dubrauszky 19 included cases of “metropathic uteri.” The theory of metropathy, still neither proven nor disproven, persists to the present era. 5,16,18,20 It is ironic that in the 19th century, knowledge of uterine atony led to the hypothesis that myometrial histopathology (metropathy) could cause serious abnormal bleeding, and that we now suggest the pathophysiology of myometrial involution may lead to uterine atony.…”

“…However, increased intramural pressure in the growing myometrium of early pregnancy—associated with the palpable bump in the abdomen that is a sign of early pregnancy—may lead to venous obstruction, with endometrial vascular ectasia, fibrin thrombi, and stromal breakdown, causing early pregnancy bleeding. 16,18,28…”

“…This consideration and illustration of the histopathology of myometrial involution leads us to suggest that this constellation of findings in postpartum hysterectomies may qualify as “postpartum metropathy.” 5,18,39 We believe that it is logical to suggest that normal myometrial contractility may not return until involution is completed, when both excess interstitial collagen is resorbed, and normal intercellular connections between myocytes are re-established. It is also logical to suggest that myocyte dropout and myocyte disconnection might cause myometrial dysfunction.…”

“…Weakening of isthmic muscle may lead to outward ballooning (isthmic aneurysms) in 20% of those who have undergone Cesarean section, with associated postpartum hemorrhage. 5,18,45 This has also been referred to as focal atony of the lower uterine segment, isthmocele, or uterine diverticulum. 5,18,45…”