| Objective: To explore morphological law of continual thin-layer cross section of pelvic floor structure as well as SCT and MRI manifestations; establish three-dimensional visible digital model of pelvic floor muscle; evaluate relationship of three-dimensional visible model of living pelvic floor muscle with that of cadaver as well as clinical significance of three-dimensional reconstruction; formulate the criteria for thickness, length and angle of ARA and PR at resting and exertion of normal human; compare the value and limitation of defecography, SCT and MRI in diagnosis of puborectalis syndrome (PRS) so as to provide theoretical basis for clinical selection of examination methods and surgical operations.Materials and methods: 1) Six adult cadaver specimens that were soaked in 10% formalin (no pelvic floor lesion was found by SCT and MRI before slicing) were used in the study. All but one female cadaver used for sagittal slicing received cross section slicing. A total of 56 healthy volunteers (control group) were further selected for cross section scanning by SCT and MRI, and sagittal coronal scanning by MRI at resting and exertion. The continual cross section of important structure of pelvic floor was observed and marked for comparison with images of SCT and MRI. 2)The continual cross-section visible images (435 pieces from the 1845th lamina to the 2280th lamina) at superior margin of iliac crest to inferior margin of ischial tuberosity from the 4th adult cadaver specimen and continual cross-section SCT images (250 pieces) at superior margin of iliac crest to inferior margin of ischial tuberosity at resting and exertion from one healthy female volunteer were collected to identify, mark and outline important structures of pelvic floor at every layer by using three-dimensional reconstruction software 3Ddoctor and to three-dimensionally reconstruct and display pelvic floor, levator ani muscle, internal obturator muscle, uteri, rectum and bladder by using surface draw reconstruction method. 3)62 cases of PRS (disease group) that were confirmed by defecography received dynamic cross-section SCT and MRI as wellas sagittal and coronal MRI scanning. Then, anorectal angle (ARA), length and depth of PRS impression, depth and angle of PRS were measured to make a contrast with results of defecography, dynamic SCT and MRI of pelvic floor in 56 healthy volunteers.Results: 1) The continual visible thin-layer cross section of the pelvic floor displayed clearly ends, direction, sizes and adjacent structures of the pelvic floor and had good corresponding relation with corresponding SCT and MRI cross section images. The comparative results showed that there was significant difference between morphology of the pelvic floor muscle and that of normal human and that pubococcygeus muscle, puborectalis and pubovaginalis were all arc and strap-shaped cross section protruding posterolaterally. While, in normal human, pubococcygeus muscle, puborectalis and pubovaginalis appeared level strap-shaped cross section, hiatus of pelvic diazoma was enlarged. Sagittal plane of the cadaver showed that iliococcygeus muscle was arc and strap-shaped cross section with slight posterior and inferior protruding in the cadavers but vault and strap-shaped cross section with a little anterior protruding in normal humans. Coronal section of cadaver showed that tilt angle (formed between horizon of iliococcygeus muscle and pelvis) of the iliococcygeus muscle was wider than that of the normal human.2) The continual digitized visible thin-layer cross section clearly displayed funnel shaped three-dimensional pelvic floor of both cadavers and normal human. However, the pelvic floor form of the cadavers showed minor difference with that of the normal human, ie, the pelvic floor was under asthenia, protruding at posterior and inferior direction, with rather big hiatus of pelvic diazoma in the cadavers; while, the pelvic floor was at a state of adduction, with small hiatus of pelvic diazoma. Three-dimensional digitized visible constructed via pelvic SCT cross section images at exertion could directly display the changes of pelvic floor muscle and pelvic organs, with function of all pelvic organs decreased, pelvic floor muscle protruding peripherally, pelvic volume increased, hiatus of the pelvic diazoma enlarged, and pelvic floor muscle thinned and elongated.3) In control group (56 cases), PR was (2.58±0.46) mm thick (51 cases), (133.62±15.75) mm long with angle of (62.68±11.59)° at resting but (1.98±0.75) mm thick, (161.27±15.58) mm long with angle of (39.74±ll.76)° at exertion. Compared with PR at resting, PR at exertion was 0.60 mm thinner, 27.65 mm longer with angle decrease of 22.94° , with very significant difference (PO.01). In disease group (62 cases), PR was(5.61±1.27) mm thick (50 cases), (134.88±15.75) mm long with angle of (65.98±11.61)° at resting but (5.48±1.35) mm thick, (141.46±15.59) mm long with angle of (58.61±11.87) ,at exertion. Compared with at resting, PR at exertion was 0.13 mm thinner, 6.58 mm longer with angle decrease of 7.37° , with insignificant difference (P>0.05). There was a very significant difference between thickness, length, angle of PR in disease group and that in control group (PO.01). In control group, ARA was (91.73±10.59)° at resting but (126.64±10.23)° at exertion, with 34.91° more compared with that at resting, with very significant difference (P<0.01). In disease group, ARA was (88.47±11.35)° at resting (49 cases) and (77.59±10.98)° at exertion, with 10.88° less compared with that at resting. PR impression was (36.5±0.46) mm long and (17.9±0.37) mm deep. ARA was (88.73±11.36)° both at resting or exertion, with no changes in 13 cases that excluded no Barium or just a bit of Barium, combined with postpon syndrome. There was a very significant difference upon ARA change between disease group and control group (P<0.01). Nonetheless, there showed insignificant difference upon thickness, length and angle of PR between the left and the right sides, between cadaver and healthy volunteer at resting, and between SCT and MRI (P>0.05), so was the length and thickness of ARA and PR measured by defecography and MRI (P>0.05). The results showed that PR in 12 cases out of the disease group with ARA changes was not thick and that thickness of PR at exertion was not reduced compared with that at resting, as might be due to PR spasm (24.5%). There still found that PR thickness was asymmetry at both sides in 5 cases (8.92%) in control group, with the right PR thinner than the left one, as possibly related to PR growth.Conclusions.- Thin-layer cross section and three-dimensional digitized visible model of pelvic floor can display clearly ends, direction, sizes and adjacent structures, explain the morphological law of continual cross section of complex anatomic structure of pelvic floor muscles, compare the morphologic structure of cadavers and normal humans and provide morphological evidence for diagnosis and treatment of functional diseases of the pelvic floor. In the meantime, the diagnostic value and limit of defecography, dynamic SCT and MRI in PRS was evaluated objectively. It is pointed out that thickness, length and angle of ARA and PR measured by MRI can be used as accurate and reliable criteria and that PRS should be first examined by MRI. The normal criteria for thickness, length and angle of ARA and PR at resting and exertion are formulated and the way on how to judge if PRS iscaused by PR thickening or spasm based on thicknes, length and angle and changes of ARA and PR is ascertained, as caters important examination method and image diagnostic evidence and plays significant role in guiding selection of suitable therapeutic scheme for PRS.
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