子宫腺肌症常见和不常见MRI表现中英文对照

1、子宫腺肌症常见和不常见MRI表现中英文对照Adenomyosis is a common nonneoplastic gynecologic disease characterized by the presence of ectopic endometrium within the myometrium .Adenomyosis typically affects multiparous, premenopausal women over 30 years of age and may cause dysmenorrhea, menorrhagia, and abnormal genital

2、 bleeding .子宫腺肌症是一种常见的非肿瘤性妇科疾病，是发生在子宫肌层的子宫内膜异位症。子宫腺肌症是一种常见的非肿瘤性妇科疾病，是发生在子宫肌层的子宫内膜异位症。其主要发生于超过其主要发生于超过3030岁岁，绝经前的经产妇并且可能引起痛经，月经过多和不正常的阴道出血的症状。，绝经前的经产妇并且可能引起痛经，月经过多和不正常的阴道出血的症状。Magnetic resonance (MR) imaging is a noninvasive modality with high sensitivity and specificity for diagnosis of adenomyosis

3、. In cases of an enlarged uterus revealed with ultrasonography, MR imaging allows differentiation of adenomyosis from leiomyoma or other pathologic conditions owing to its excellent tissue contrast resolution .磁共振（磁共振（MRMR）成像是一种非侵入性的检查方式，其在诊断子宫腺肌症上具有高的灵敏度和特异度。成像是一种非侵入性的检查方式，其在诊断子宫腺肌症上具有高的灵敏度和特异度。当超声

4、检查中发现子宫增大时，磁共振由于其出色的组织对比分辨率可以把子宫腺肌症与子宫肌瘤当超声检查中发现子宫增大时，磁共振由于其出色的组织对比分辨率可以把子宫腺肌症与子宫肌瘤或其他疾病鉴别出来。或其他疾病鉴别出来。 IntroductionOn T2-weighted images, typical adenomyosis appears as an ill-demarcated low-signal-intensity lesion with uterine enlargement. However, various physiologic or pathologic states may affe

5、ct the MR imaging appearance of adenomyosis and may result in a tumorlike appearance 在T2WI上，子宫腺肌症的典型表现为一个边界不清的低信号强度病变伴随着子宫增大。然而，多种生理和病理改变也许会影响子宫腺肌症的MRI表现并且会导致其出现肿瘤样的表现Specific topics discussed are MR imaging manifestations of typical adenomyosis, atypical MR imaging manifestations of adenomyosis, pi

6、tfalls in diagnosis of adenomyosis, 讨论的具体话题包括子宫腺肌症的典型MRI表现，子宫腺肌症的不典型MRI表现，子宫腺肌症的诊断误区IntroductionMR Imaging Manifestations of Typical Adenomyosis子宫腺肌症的典型子宫腺肌症的典型MRI表现表现 Typical AdenomyosisAt pathologic analysis, adenomyosis is characterized by the presence of ectopic endometrial glands and stroma wit

7、hin the myometrium with hypertrophy and hyperplasia of smooth muscleAdenomyosis may affect the uterine myometrium diffusely and result in a diffusely enlarged uterus, or it may be localized as an adenomyoma.病理分析，子宫腺肌症的特征性表现是子宫肌层内异位的子宫内膜腺体和间质的存在和平滑肌的肥大增生。子宫腺肌症也许会弥漫性的影响子宫肌层并导致子宫弥漫性的增大，或者会作为腺肌瘤局限性的影响肌层

8、A cut section of a diffusely adenomyotic uterus shows thickened myometrium due to the ill-defined adenomyosis; the thickened myometrium is composed of haphazardly distributed hypertrophied muscular trabeculae surrounding ectopic endometrial tissue (Fig 1) . Brownish old hemorrhagic foci correspondin

9、g to hemolysed blood and hemosiderin pigment deposits may be contained within the area of adenomyosis弥漫型腺肌型子宫的横断面显示由于界限不清的子宫腺肌病导致肌层增厚。肥厚的肌层是由随弥漫型腺肌型子宫的横断面显示由于界限不清的子宫腺肌病导致肌层增厚。肥厚的肌层是由随意分布的肥大性肌小梁及周围的异位子宫内膜组织所构成意分布的肥大性肌小梁及周围的异位子宫内膜组织所构成（图（图1）。）。褐色的旧出血灶也许对应着子宫腺肌症区域内的出血和含铁血黄素沉积褐色的旧出血灶也许对应着子宫腺肌症区域内的出血和含铁血

10、黄素沉积 Typical Adenomyosis1A1BFigure 1. Adenomyosis in a 47-year-old woman. 47岁女性，子宫腺肌症患者，(a) Photograph of the cut surface of the gross specimen shows diffusely thickened myometrium. (b) photomicrograph (hematoxylin-eosin stain) shows ectopic endometrial glands and stroma (arrow) surrounded by hypert

11、rophied smooth muscle.a.大体标本的切面照片显示弥漫性增厚的子宫肌层 b.显微镜下照片（HE染色）显示异位的子宫内膜腺体和间质和周围的肥厚的平滑肌 Typical adenomyosis appears as an ill-demarcated low-signal-intensity area on T2-weighted images owing to abundant smooth muscle proliferation (Fig 2) .Because adenomyotic endometrium looks like the basalis endometr

12、ium, which seldom responds to hormonal stimuli, cyclic changes including degeneration, bleeding, and regeneration are less common in adenomyosis than in endometriosis . 子宫腺肌症的典型表现是在T2WI上有一界限不清的低信号区域，这是由于丰富的平滑肌细胞增殖。因为腺肌症子宫内膜跟基底子宫内膜一样，很少对激素的刺激做出反应，所以与其他子宫内膜异位症相比，包括变性，出血，再生这样的周期性的变化较少出现在子宫腺肌症中On T2-wei

13、ghted MR images, ectopic endometrium appears as small high-signal-intensity areas like normal endometrium (Fig 2). Small cysts may also appear as high-signal-intensity spots on T2- weighted images.Sometimes, hemorrhagic foci appear as 13mm high-signal-intensity foci on T1-weighted images owing to th

14、e T1-shortening effects of methemoglobin (Fig 2)在T2WI图像上，异位子宫内膜表现为跟正常子宫内膜一样的小的片状高信号，小的囊肿也可能在T2WI上表现为点状高信号。有时候由于高铁血红蛋白T1缩短效应的影响，出血灶在T1WI上表现为1-3mm的高信号病灶 Typical AdenomyosisSusceptibility-weighted imaging is sensitive for old hemorrhagic foci, which appear as spotty signal voids owing to the T2*-shorte

15、ning effects of hemosiderin . At diffusion-weighted imaging, adenomyosis has low to intermediate signal intensity, a finding consistent with its benign, nonneoplastic nature (Fig 3) 磁敏感加权成像对陈旧出血灶很敏感，由于含铁血黄素T2缩短效应的影像，表现点状低信号。在弥散加权像上，子宫腺肌症表现为低到中等信号强度，这种表现其实与它是良性，非肿瘤性病变这种性质相一致However, there is no direc

16、t correlation between signal intensity at diffusion-weighted imaging and malignancy; most malignant tumors have very high signal intensity at diffusion-weighted imaging, a finding that reflects the long T2 relaxation time and restricted diffusion due to high cellularity.然而，DWI上信号强度和恶性病变之间并没有直接的相关性；大

17、多数的恶性肿瘤在DWI上有非常高的信号强度，这反映了由于长的T2弛豫时间和高的细胞密度导致的扩散受限。 Typical AdenomyosisFigure 2. Adenomyosis in a 46-year-old woman. 46岁女性，子宫腺肌症患者(a) Sagittal T2-weighted fast spin-echo MR image shows an enlarged uterus with an ill-defined low-signal-intensity lesion (arrow) in the posterior myometrium. The lesion

18、contains multiple small high-signal-intensity areas, which represent ectopic endometrial tissue and small cysts.矢状位T2加权快速自旋回波MR图像显示子宫增大，伴随一个子宫肌层后壁内界限不清的低信号强度的病变（箭头处），病变包含多个小的高信号的区域，其代表了子宫内膜异位组织和小囊肿 (b) Sagittal T1-weighted spin-echo MR image shows high-signal-intensity spots (arrow), which correspon

19、d to some of the small high-signal-intensity areas seen on the T2-weighted image.The high-signal-intensity spots represent hemorrhage within the ectopic endometrial tissue.矢状位T1加权自旋回波MR图像显示了点状高信号，它们对应了在T2WI上看到的一些小的高信号区域。这些点状高信号代表了子宫内膜组织内的出血Figure 3. Adenomyosis in a 42-year-old woman. (a) Sagittal d

20、iffusion-weighted echo-planar MR image (b = 800 sec/mm2) shows an enlarged uterus with an ill-defined lesion of low to intermediate signal intensity (arrow) in the posterior myometrium. (b) Corresponding apparent diffusion coefficient (ADC) map shows no prominent decrease of ADC value in the area of

21、 adenomyosis (arrow).a.矢状位扩散加权回波平面MR图像(b = 800 sec/mm2)显示增大的子宫伴随后壁肌层内界限不清的病变，呈低到中等信号强度（箭头）。b.相应的ADC图上在子宫腺肌症的区域内没有显示出明显的ADC值的下降Because adenomyosis may show various degrees of enhancement after administration of contrast medium, contrast-enhanced study does not contribute to diagnostic accuracy (Fig 4

22、).Dynamic contrast-enhanced imaging may have greater accuracy than T2-weighted imaging when adenomyosis and endometrial cancer coexist (16). 因为在注射造影剂后，子宫腺肌症可能显示为不同程度的强化，所以关于其对比增强的研究对诊断的准确性没有帮助（图4）。 当子宫腺肌症和子宫内膜癌同时存在时动态对比增强图像也许会比T2加权图像更准确However, the heterogeneous enhancement of adenomyosis may cause

23、inaccuracy when evaluating the depth of myometrial invasion by coexisting endometrial cancer; diffusion-weighted imaging may be helpful in accurately determining the depth of myometrial invasion .然而当并发子宫内膜癌时，子宫腺肌症不均质的强化可能会导致评估肌层浸润深度的不准确；扩散加权成像也许会帮助准确的确定肌层浸润深度 Typical AdenomyosisDiffusion-weighted Im

24、agingDiffusion-weighted imaging allows visualization of the local microstructural characteristics of water diffusion. The signal intensity seen on diffusion-weighted images is a combination of the degree of water diffusion and the signal intensity of the underlying T2-weighted images.扩散加权图像能够可视化水分子扩

25、散的微观结构特征，在DWI上看的信号强度是水分子扩散程度和基础T2加权图像信号强度的结合。In oncologic imaging, various malignant tumors may show high signal intensity at diffusion-weighted imaging due to their high cellularity and long T2 relaxation time 在肿瘤成像上，由于高的细胞密度和长的T2弛豫时间，各种恶性肿瘤在DWI上显示为高信号。 ADC measurement yields quantitative informati

26、on about tissue structure that is based on the molecular motion of water. Malignant lesions with increased cellularity show low ADC values, whereas relatively hypocellular benign lesions and normal structures tend to show relatively higher ADC values.ADC图以水分子的运动为基础来测量组织结构的定量信息。高的细胞密度大的病变表现出低的ADC值，而相

27、对低度增生的良性病变和正常组织显示相对高的ADC值 Typical AdenomyosisFigure 4. Adenomyosis in a 47-year-old woman. 47岁女性，子宫腺肌症患者(a) Sagittal T2-weighted fast spin-echo MR image shows an enlarged uterus with an ill-defined low-signal-intensity lesion (arrow) in the posterior myometrium. The lesion contains multiple small hi

28、gh-signal-intensity areas.(b) Unenhanced (upper left), early arterial phase (upper right), late arterial phase (lower left), and venous phase (lower right) images, obtained with a dynamic gadolinium-enhanced three-dimensional fast spoiled gradient-echo sequence with fat suppression, show heterogeneo

29、us and gradual enhancement of the lesion.a.矢状位T2加权快速自旋回波MR图像显示子宫增大伴随子宫肌层后壁内界限不清的低信号强度病变。病变内包含多个小的高信号强度区域b.由一个压脂动态钆增强型三维快速小角度梯度回波序列获得平扫（左上图），动脉早期相（右上图），动脉晚期相（左上图），以及静脉相（右下图），病变表现为不均匀和渐进性的强化。Atypical MR Imaging Manifestations of Adenomyosis子宫腺肌症的非典型子宫腺肌症的非典型MRI表现表现Atypical Adenomyosis Various physiolo

30、gic or pathologic states may affect the MR imaging appearance of adenomyosis: amount of functional endometrial tissue, phase of the menstrual cycle, endogenous hormonal abnormality, and exogenous hormonal stimulation. Secretory transformation of adenomyotic endometrium including stromal decidualizat

31、ionmay cause a heterogeneous increase in signal intensity on T2-weighted images.多种生理或病理状态可能会影响子宫腺肌症的MRI表现：功能性子宫内膜组织的量，月经周期的阶段，内源激素的异常，外源激素的刺激。腺肌症子宫内膜的分泌转化包括间质蜕膜化会导致T2WI上信号强度不均质的提高This phenomenon may be encountered during gestation and exogenous progestational therapy or even in patients without spec

32、ific hormonal stimulation. Congestion or edematous change may also increase the signal intensity of adenomyosis diffusely or focally on T2-weighted images (Fig 5). 这种现象可能发生于怀孕期间，外源性孕激素治疗期间，或者甚至在没有特定激素刺激的患者身上。充血或水肿的变化也可能会在T2WI上弥漫性增加子宫腺肌症的信号强度或者局部信号强度（图5）。In such conditions, MR imaging manifestations

33、may fluctuate, and follow-up MR imaging may be helpful for diagnosis. Gonadotropin-releasing hormone analog is used in the treatment of adenomyosis. After hormonal therapy or menopause, an area of adenomyosis may shrink with decreased signal intensity on T2-weighted images(Fig 6)在这种情况下，MRI表现会变化较大，再一

34、次的复查对诊断有帮助。促性腺激素释放激素类似物被用于治疗子宫腺肌症。激素治疗后或在绝经期时，子宫腺肌症的面积可能会萎缩，并伴随着T2WI上信号强度的降低(图6)。Atypical Adenomyosis Figure 5. Adenomyosis with focal edema in a 54-year-old woman. (a) Sagittal T2-weighted fast spin-echo MR image shows an enlarged uterus with an ill-defined low-signal-intensity lesion in the poster

35、ior myometrium. The low-signal-intensity lesion contains a focal high-signal-intensity masslike area (arrow).(b) On diffusion weighted echo-planar MR image (b = 800 sec/ mm2), the high-signal-intensity masslike area in a sagittal shows no increase in signal intensity (arrow). a.矢状位T2加权快速自旋回波MR图像显示增大

36、的子宫伴随子宫后壁内界限不清的低信号强度病变。这个低信号病变内包含一个肿块样高信号强度区域（箭头）b.在矢状位扩散加权平面回波MR图像上 (b = 800 sec/ mm2) ，这个高信号强度肿瘤样区域没有显示信号强度的增高（箭头）Figure 5.（c ） On an image from MR spectroscopy, the high-signal-intensity masslike area shows a low choline peak (Cho) at 3.2 ppm. Biopsy revealed benign adenomyotic tissue with stroma

37、l edema. The signal intensity of the masslike area is decreased on follow-up T2-weighted images obtained 3 months later. c.在磁共振波谱上，这个高信号强度的肿块样区域在3.2ppm处显示为低的胆碱峰（Cho）。活检发现良性子宫腺肌组织间质水肿，这个肿块样区域的信号强度在3个月后的T2WI图像上降低。MR spectroscopyFigure 6. Adenomyosis in a 50-year-old woman before and after hormonal the

38、rapy with gonadotropinre leasing hormone analog.一个50岁女性，子宫腺肌症患者，促性腺激素释放激素类似物治疗前后(a)Axial T2-weighted fast spin-echo MR image shows adenomyosis as an ill-defined heterogeneous low-signal-intensity lesion with linear or reticular high-signal-intensity areas in the anterior myometrium (arrow). (b) Axia

39、l T2-weighted fast spin-echo MR image obtained after hormonal therapy shows decreased volume and signal intensity of the area of adenomyosis (arrow). a.在轴位T2加权快速自旋回波MR图像上，子宫腺肌症显示为边界不清的不均匀的低信号强度病变伴随肌层前壁线状或网状高信号强度区域（箭头） b.激素治疗后，获取的轴位T2加权快速自旋回波MR图像显示子宫腺肌症区域的面积和信号强度都下降了In such conditions, MR imaging man

40、ifestations may fluctuate, and follow-up MR imaging may be helpful for diagnosis. Gonadotropin-releasing hormone analog is used in the treatment of adenomyosis. After hormonal therapy or menopause, an area of adenomyosis may shrink with decreased signal intensity on T2-weighted images(Fig 6) 在这种情况下，

41、MRI表现会变化较大，再一次的复查对诊断有帮助。促性腺激素释放激素类似物被用于治疗子宫腺肌症。激素治疗后或绝经期子宫腺肌症的面积可能会萎缩，并伴随着T2WI上信号强度的降低。 Diffusion-weighted imaging with ADC measurement may provide another clue for the diagnosis, because these conditions (secretory transformation, decidualization, congestion or edema) usually increase the ADC in ti

42、ssues. A relatively high ADC in adenomyotic lesions with high signal intensity on T2-weighted images may allow differentiation from malignant lesions, which have a low ADC due to their high cellularity (Fig 5) (15). 弥散加权成像图像上ADC值的测量可能提供诊断的另一条线索，因为在这些情况下（分泌转化，蜕膜变，充血或水肿）通常会增加组织的ADC值。子宫腺肌症病灶的一个相对高的ADC值

43、和高的T2信号强度可以将其从恶性病变中鉴别出来，因为恶性病变由于其高的细胞密度导致低的ADC值MR spectroscopy may also provide a clue for the diagnosis, because these benign adenomyotic conditions do not show high metabolic activity. A relatively low choline peak in adenomyotic lesions may allow differentiation from malignant tumors, which show

44、a high choline peak due to their high metabolic activity (Fig5)磁共振质子波谱也可以提供诊断线索，因为这些良性的腺肌并没有表现为高的代谢活动。子宫腺肌症病变的一个相对低的胆碱峰有助于将其与恶性肿瘤鉴别开，因为恶性肿瘤由于其高的代谢活动显示为高的胆碱峰。Atypical Adenomyosis Pitfalls in Diagnosis of Adenomyosis子宫腺肌症诊断中的陷阱子宫腺肌症诊断中的陷阱The uterine body may show physiologic changes during the menstru

45、al cycle. The low-signal-intensity junctional zone and adenomyosis are well visualized due to increased signal intensity of the myometrium in the secretory phase (luteal phase). 子宫体在月经周期中表现了生理性的变化。由于在分泌期（黄体期）时子宫肌层信号变高，导致能清楚的看到低信号的结合带和子宫腺肌症Decreased signal intensity of the myometrium in the menstrual

46、early proliferative phase (follicular phase) may cause widening of the junctional zone, which mimics diffuse adenomyosis. Therefore, MR imaging for the evaluation of a uterine myometrial lesion should be performed in the late proliferativesecretory phase (Fig 7)肌层在月经早期增殖期（卵泡期）信号强度的下降会引起结合带的增宽，使其像弥漫性

47、子宫腺肌症。因此MRI对子宫肌层的评价应该在增生晚期-分泌期进行（图7）Physiologic Changes in the Uterine Body during the Menstrual Cycle 在月经周期中子宫体的生理变化在月经周期中子宫体的生理变化Figure 7. Subserosal adenomyosis-like lesion (invasive solid endometriosis) in a 33-year-old woman during different phases of the menstrual cycle. (a) Sagittal T2-weight

48、ed fast spin-echo MR image obtained in the early proliferative phase shows decreased signal intensity of the myometrium. The boundary between the myometrium and a subserosal adenomyosis-like lesion (arrow) is obscure.(b) Sagittal T2-weighted fast spin-echo MR image obtained in the late secretory pha

49、se shows increased signal intensity of the myometrium. The low-signal-intensity junctional zone and the subserosal adenomyosis-likelesion (arrow) are clearly visualized.33岁女性，浆膜下的子宫腺肌样病变，在月经周期的不同阶段a.在增殖早期时相获取的矢状位T2加权快速自旋回波MR图像显示肌层信号强度的下降。肌层和浆膜下子宫腺肌样病变之间的界限是模糊的b.在分泌晚期阶段获得的矢状位T2加权快速自旋回波MR图像显示肌层信号强度增高。

50、低信号强度的结合带和浆膜下腺肌样病变清晰可见Various benign conditions and malignant tumors may mimic adenomyosis: physiologic myometrial contraction, myometrial involvement by pelvic endometriosis, low-grade endometrial stroma sarcoma (LG-ESS), and myometrial metastases 多种良性改变和恶性肿瘤类似于子宫腺肌症：生理肌层收缩，肌层受累的盆腔子宫内膜异位症，低度恶性子宫内膜间

51、质肉瘤（LG-ESS），和肌层转移 Transient myometrial contraction as a physiologic phenomenon may mimic adenomyosis; this appearance may disappear on subsequent images or at cine MR imaging, whereas focal adenomyosis persists on subsequent images or at cine MR imaging (Fig 8) In the pregnant uterus, myometrium adj

52、acent to the implant site may show low signal intensity, which reflects blood supplying a contraction; this finding mimics physiologic contraction or focal adenomyosis (Fig 9) . 作为一种生理现象的瞬态肌层收缩类似于子宫腺肌症，这种外观可能会消失在随后的图像或电影MRI图像，而局灶性子宫腺肌病持续的存在于随后的图像或电影MR成像。在怀孕的子宫，子宫肌层植入的地方表现为低信号，这反映了血液供给的收缩；这个表现类似于生理性收

53、缩或局灶性腺肌病。Contractions in the pregnant uterus are commonly seen and usually do not present a diagnostic dilemma; however, radiologists who are not familiar with MR imaging of pregnant women may misdiagnose the contraction 孕妇子宫的收缩很常见，通常不存在诊断的孕妇子宫的收缩很常见，通常不存在诊断的难题，然而，不熟悉怀孕女性难题，然而，不熟悉怀孕女性MR成像的放射学医生可能会将子

54、宫收缩误诊成像的放射学医生可能会将子宫收缩误诊Benign and Malignant Mimics of Adenomyosis 类似于子宫腺肌症的良性和恶性病变类似于子宫腺肌症的良性和恶性病变Figure 8. Physiologic transient myometrial contraction in a 32-year-old woman. 发生在一个32岁女性的生理性瞬间肌层收缩Sagittal T2-weighted fast spin-echo MR image shows focal low-signal-intensity bulging of the myometrium

55、 (arrow), a finding that mimics adenomyosis. This finding disappeared on subsequent T2-weighted images.矢状位T2加权快速自旋回波MR图像显示为子宫肌层局灶性低信号强度的膨胀（箭头），这个表现类似于子宫腺肌症。其在接下来的T2WI上消失了。Pitfalls in Diagnosis Figure 9. Transient myometrial contraction during pregnancy in a 31-year-old woman. 一个31岁女性怀孕期间的瞬间肌层收缩(a) A

56、xial T2-weighted fast spin-echo MR image shows a localized area of low signal intensity (arrow) in the uterus, a finding that mimics adenomyosis. Because a rapid T2-weighted sequence (eg, half-Fourier acquisition single-shot turbo spin-echo or single-shot fast spin-echo) was not used, depiction of t

57、he embryo-fetus is poor. (b) Axial susceptibility-weighted gradient-echo MR image shows absence of signal voids (arrow) within the low-signal-intensity area . However, absence of signal voids at susceptibility-weighted imaging should not be considered to exclude adenomyosis. To establish the diagnos

58、is of a contraction, it would be critical to show the low-signal-intensity area on subsequent T2-weighted images.a.轴位T2加权快速自旋回波MR图像显示子宫内一个局部低信号，类似于子宫腺肌症，因为快速T2加权序列没有使用，导致显示胎儿显示较差b.轴位SWI图显示低信号区域内没有点状低信号，然而在SWI图上缺乏点状低信号并不能排除子宫腺肌症。为了确定生理收缩的诊断，在随后的T2加权图像上显示低信号强度的区域至关重要Susceptibility-weighted imaging can

59、 show small hemorrhagic foci in adenomyosis as spotty signal voids and may be helpful in differentiating adenomyosis from focal contraction (Fig 10) . On the other hand, absence of signal voids at susceptibility-weighted imaging should not be considered to exclude adenomyosis. 磁敏感图能显示子宫腺肌症中的小的出血灶，表现

60、为点状低信号，可以帮助鉴别子宫腺肌症和局灶性收缩，另一方面，磁敏感图上点状低信号的不存在不应该认为可以排除子宫腺肌症Adenomyosis is due to benign invasion of the myometrium by ectopic endometrium and is a different entity from endometriosis . However,some adenomyosis-like lesions may be situated in the subserosal region apart from the junctional zone (Figs