MORPHOMETRIC STUDY ON PULMONARY ARTERIAL THICKNESS IN PULMONARY HYPOPLASIA
P. J. Barth, MD, and J. Riischoff, MD
0
Department of Pathology, D-3550
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
Marburg, Baldingerstrasse, Germany
0 This study addresses the qlustion of whether pulmonary h@p& ir asso&& with structuralc-es of the p u l m r y arlerie. Quuntilative ( d i a l t h i h s , exlemoc radius) and qdilatibe (airway he/) parmneters of pulmonary arten’es were assessed in tight hypoplastic lunps and &ht lungs fimn age-makhtd fetuses withoui underlyinp. primry p d m r y disease. Thc geslatwnal ages ranged j o m 16 to 40 weeks. Relotive medial thickness of Ihe pulmmvlry was related tn the aimd radius and to the tvpe of accompanyiq airway. Medial thickness was s;Sntf;cant~higher in pulmonary h$n$du.& than in nonnal fdlungs. In contrast to n o d fa1lungs, rnurcular arteries cxtmded to the intra-acinar level in pulmonmy h@p&. Thcse arteries hnd medial thickness valua up to a mwimum 480%.
KEY WORDS: Pulmonary arteries, pulmonary hypoplasia, morphonutry.
INTRODUCTION The diagnosis of pulmonary hypoplasia (PH) is based on morphologic criteria derived from the underdevelopment of peripheral airways. Accordingly, the lungs are remarkably reduced in weight (1), show few immature alveoli and an immature duct system (2, 3), and exhibit a thickened interstitiurn (4, 5). A review of the literature shows that the investigators’ interests have mostly been directed toward the parenchymal aspects of PH and vascular changes have seldom been taken into consideration (1, 4-10). Investigations of the vascular changes in pulmonary hypoplasia are rare (7). Hislop et al. (7) demonstrated the wall thickness of pulmonary arteries in cases of renal agenesis to be less than the normal fetal level. By contrast, two of three cases of renal dysplasia had normal fetal wall thickness and in a third case the arterial walls were thicker than normal. The study (7) suffers, as do several others (1 1-14), from the fact that the estimation of relative media thickness (RMT) is based on direct measurement of medial thickness along one diameter only. This method has already been criticized by several authors (15-17). Address reprint requests to Dr. P. J , Barth, MZ fur Pathologie, Baldingerstrasse, W-3550 Marburg/ Lahn, Germany. Pediatric Patholoo, 12.553463, 1992 Copyright 0 1992 by Hemisphere Publishing Corporation
653
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
654
P. J. BARTH AND J. RUSCHOFF
Cook and Yates (15) proposed using planimetric assessment of medial thickness to avoid systematic errors due to incomplete distention of the arteries and selection of unrepresentative diameters for measurement of the medial thickness. They used a camera lucida fitted to a microscope, and the shape of the vessel was drawn by hand on paper. Thus the assessment of a large number of vessels, sufficient for statistical analysis, was time-consuming and led to observer fatigue. Modern computer-aided image analysis enables the investigator to assess planimetric and histomorphometric characteristics of a chosen structure and to rapidly perform complicated mathematical procedures. Applying these modern techniques, we addressed the question of whether structural changes of the pulmonary arteries occur in pulmonary hypoplasia.
MATERIALS AND METHODS Hypoplastic lungs of eight fetuses-six with infantile polycystic kidney disease (Potter type II), one with bilateral renal agenesis, and one anencephalic fetus-were examined. In one fetus with bilateral polycystic kidney disease oligohydramnios was corrected by intrauterine instillation of artificial amniotic fluid (18, 19). Gestational ages ranged from 16 to 40 weeks. Eight stillborn infants of similar gestation served as controls. Underlying pulmonary or renal diseases were excluded by histological examination and review of the clinical files. The diagnosis of lung hypoplasia was based on the ratio of lung weight to body weight (lung/body weight ratio 50.015 at 40 pm. The upper limit was fixed at 150 pm because the R M T curves of arteries of R > 150 pm showed a parallel course in both groups. Because measurements were done by planimetry and
661
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
ARTERIES IN PULMONARY HYPOPLASIA
readings were consolidated into one value (AMT), we consider our method to be superior to those previously reported. The major disadvantage of the method presented here is that it can only be applied to vessels cut in good cross section (15). Further studies will have to show whether obliquely cut vessels can also be used for assessment of R M T and AMT. Analysis of A M T and vessel radius showed that medial thicknesses of arteries of the same size are significantly thicker in PH than in the controls. This statement is based on purely quantitative analysis and has to be completed by qualitative assessment of the vasculature by considering the level of the accompanying airways. Our investigation showed that in PH, muscular arteries extend to more distal airway levels and that smaller arteries are muscularized. In the normal fetal lung no muscular arteries are seen within the acinus (1 1, 13). Our study confirms this finding for gestational ages between the 17th and 40th gestational weeks. By contrast, in PH, muscular arteries extend peripherally to the intra-acinar level. One possible explanation for this finding is that, in contrast to the reduced development of lung parenchyma, normal growth of
60.
Hypoplasla
40.
20.
0
0
-0
0
;
'controls
O
d
20.
0
D O L
eo
0
Hypopl88la
60.
0
40 D
Controls
20.
20
I
I 16
20
26
30 36 Gestetlonal w e k
40
Hypoplasla
-
0
-
d 0
Q
1 15
0
L
26
25
30 Gestatlonal week
35
40
FIGURE 6. Synopsis of the vessel parameters R M T (upper row) and external radius (lower row) of intraacinar arteries (right column) and arteries accompanied by a terminal bronchiole (left column). For each case mean R M T and mean external radius were computed for the different types of related airways. Linear curve fit, confidence limits not displayed. (0) Controls; (0)PH group.
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
662
P. J. EARTH AND J. RUSCHOFF
-
-
FIGURE 7. Microphotograph of an intra-acinar muscular artery in pulmonary hypoplasia. The vessel is surrounded by a cuff of dense connective tissue. R M T 2 3 . 3 % , external radius 32 p n . Microscopic magnification X 460.
arterial smooth muscle takes place in P H , leading to a relative excess of vascular smooth muscle mass. This excess of arterial smooth muscle results in elevated R M T of arteries and extension of musculature to more distal airways, not muscularized during normal lung development. The correlation between RAC and AMT (Fig. 5) supports this hypothesis; with rising RAG, which reflects the development of lung parenchyma, the relative volume of smooth musculature per vessel, measured as AMT, decreases. Our data concerning the RAC values in normal fetal lungs are similar to those already published. RAC values for lung hypoplasia differ slightly from those published by Hislop et al. (7), who reported RAC ranging from 2.5 to 3.5 for bilateral poly- or multicystic renal dysplasia (38-41 weeks of gestation). In contrast, Reale and Esterly (1) found RAC values ranging from 2.3 to 7.8 (gestational age 32-44 weeks) in infants with polycystic bilateral renal dysplasia. In oligohydramnios the alveolar-intra-amniotic pressure gradient is elevated because of decreased amniotic pressure (18). This leads to loss of lung fluid, thought to be an essential cause in the development of PH. Based on this pathogenetic concept, in order to prevent P H oligohydramnios should be corrected by intrauterine instillation of artificial amniotic fluid (18). One case (37 weeks gestation, A M T 22.576, RAC 2.2) of cystic kidney disease submitted to
ARTERIES IN PULMONARY HYPOPLASIA
663
this therapy was examined in this study; no significant difference between the AMT and RAC values of the PH group was found.
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
REFERENCES 1. Reale FR, Esterly JR. Pulmonary hypoplasia: A morphometric study of the lungs of infants with diaphragmatic hernia, anencephaly, and renal malformations. Pediatrics 1973;51:91-6. 2 . Cooney TP, Thurlbeck WM. The radial alveolar count method of Emery and Mithal: A reappraisal. 1-Postnatal lung growth. Thorax 1982;37:572-9. 3. Cooney TP, Thurlbeck WM. The radial alveolar count method of Emery and Mithal: A reappraisal. 2-Intrauterine and early postnatal lung growth. Thorax 1982;37:580-3. 4. Itoh K , Suzuki J , Sakuragi K , et al. Clinicopathological studies on pulmonary hypoplasia in very low birth weight infants. Acta Pathol Jpn 1987;37:725-36. 5. Itoh K, Itoh H. A study of cartilage development in pulmonary hypoplasia. Pediatr Pathol 1988;8:6581. (Published erratum in Pediatr Pathol 1990;10:479.) 6. George DK, Cooney TP, Chiu BK, Thurlbeck W M . Hypoplasia and immaturity of the terminal lung unit (acinus) in congenital diaphragmatic hernia. Am Rev Respir Dis 1987;136:947-50. 7. Hislop A, Hey E, Reid L. The lungs in congenital bilateral renal agenesis and dysplasia. Arch Dis Child 1979;54:32-8. 8. Potter EL. Bilateral absence of ureters and kidneys: A report of 50 cases. Obstet Gynecol 1965;25:312. 9. Potter EL. Bilateral renal agenesis. J Pediatr 1946;29:68-76. 10. Wigglesworth JS, Desai R , Guerrini P. Fetal lung hypoplasia: Biochemical and structural variations and their possible significance. Arch Dis Child 56;1981:606-15. 11. Davies G, Reid L. Growth of the alveoli and pulmonary arteries in childhood. Thorax 1970;25:66981.
12. Heath D , Edwards JE. The pathology of hypertensive pulmonary vascular disease. A description of six grades of structural changes in the pulmonary arteries with special reference to congenital cardiac septal defects. Circulation 1958;18:533-47. 13. Hislop A, Reid L. Pulmonary arterial development during childhood: Branching pattern and structure. Thorax 1973;28:129-35. 14. Hislop A, Reid L. Intra-pulmonary arterial development during fetal life-Branching pattern and structure. J Anat 1972;113:35-48. 15. Cook TA, Yates PO. A critical survey of techniques for arterial mensuration. J Pathol 1972;108:11927. 16. Fernie J M , Lamb D. New method for measuring intimal component of pulmonary arteries. J Clin Pathol 1985;38:1374-9. 17. Fernie J M , Lamb D. Method for maximising measurements of muscular pulmonary arteries. J Clin Pathol 1985;38:1380-7. 18. Nicolini U, Fisk N M , Rodeck C H , Talbert DG, Wigglesworth JS. Low amniotic pressure in oligohydramnios-Is this the cause of pulmonary hypoplasia? Am J Obstet Gynecol 1989;161:1098101. 19. Thomas IT, Smith DW. Oligohydramnios, cause of the nonrenal features of Potter’s syndrome, including pulmonary hypoplasia. J Pediatr 1974;84:811-4. 20. Emery JL, Mithal A. The number of alveoli in the terminal respiratory unit of man during late intrauterine life and childhood. Arch Dis Child 1960;35:544-7. Received October 25, 1991 Revision accepted March 23, 1992
P. J. Barth, MD, and J. Riischoff, MD
0
Department of Pathology, D-3550
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
Marburg, Baldingerstrasse, Germany
0 This study addresses the qlustion of whether pulmonary h@p& ir asso&& with structuralc-es of the p u l m r y arlerie. Quuntilative ( d i a l t h i h s , exlemoc radius) and qdilatibe (airway he/) parmneters of pulmonary arten’es were assessed in tight hypoplastic lunps and &ht lungs fimn age-makhtd fetuses withoui underlyinp. primry p d m r y disease. Thc geslatwnal ages ranged j o m 16 to 40 weeks. Relotive medial thickness of Ihe pulmmvlry was related tn the aimd radius and to the tvpe of accompanyiq airway. Medial thickness was s;Sntf;cant~higher in pulmonary h$n$du.& than in nonnal fdlungs. In contrast to n o d fa1lungs, rnurcular arteries cxtmded to the intra-acinar level in pulmonmy h@p&. Thcse arteries hnd medial thickness valua up to a mwimum 480%.
KEY WORDS: Pulmonary arteries, pulmonary hypoplasia, morphonutry.
INTRODUCTION The diagnosis of pulmonary hypoplasia (PH) is based on morphologic criteria derived from the underdevelopment of peripheral airways. Accordingly, the lungs are remarkably reduced in weight (1), show few immature alveoli and an immature duct system (2, 3), and exhibit a thickened interstitiurn (4, 5). A review of the literature shows that the investigators’ interests have mostly been directed toward the parenchymal aspects of PH and vascular changes have seldom been taken into consideration (1, 4-10). Investigations of the vascular changes in pulmonary hypoplasia are rare (7). Hislop et al. (7) demonstrated the wall thickness of pulmonary arteries in cases of renal agenesis to be less than the normal fetal level. By contrast, two of three cases of renal dysplasia had normal fetal wall thickness and in a third case the arterial walls were thicker than normal. The study (7) suffers, as do several others (1 1-14), from the fact that the estimation of relative media thickness (RMT) is based on direct measurement of medial thickness along one diameter only. This method has already been criticized by several authors (15-17). Address reprint requests to Dr. P. J , Barth, MZ fur Pathologie, Baldingerstrasse, W-3550 Marburg/ Lahn, Germany. Pediatric Patholoo, 12.553463, 1992 Copyright 0 1992 by Hemisphere Publishing Corporation
653
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
654
P. J. BARTH AND J. RUSCHOFF
Cook and Yates (15) proposed using planimetric assessment of medial thickness to avoid systematic errors due to incomplete distention of the arteries and selection of unrepresentative diameters for measurement of the medial thickness. They used a camera lucida fitted to a microscope, and the shape of the vessel was drawn by hand on paper. Thus the assessment of a large number of vessels, sufficient for statistical analysis, was time-consuming and led to observer fatigue. Modern computer-aided image analysis enables the investigator to assess planimetric and histomorphometric characteristics of a chosen structure and to rapidly perform complicated mathematical procedures. Applying these modern techniques, we addressed the question of whether structural changes of the pulmonary arteries occur in pulmonary hypoplasia.
MATERIALS AND METHODS Hypoplastic lungs of eight fetuses-six with infantile polycystic kidney disease (Potter type II), one with bilateral renal agenesis, and one anencephalic fetus-were examined. In one fetus with bilateral polycystic kidney disease oligohydramnios was corrected by intrauterine instillation of artificial amniotic fluid (18, 19). Gestational ages ranged from 16 to 40 weeks. Eight stillborn infants of similar gestation served as controls. Underlying pulmonary or renal diseases were excluded by histological examination and review of the clinical files. The diagnosis of lung hypoplasia was based on the ratio of lung weight to body weight (lung/body weight ratio 50.015 at 40 pm. The upper limit was fixed at 150 pm because the R M T curves of arteries of R > 150 pm showed a parallel course in both groups. Because measurements were done by planimetry and
661
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
ARTERIES IN PULMONARY HYPOPLASIA
readings were consolidated into one value (AMT), we consider our method to be superior to those previously reported. The major disadvantage of the method presented here is that it can only be applied to vessels cut in good cross section (15). Further studies will have to show whether obliquely cut vessels can also be used for assessment of R M T and AMT. Analysis of A M T and vessel radius showed that medial thicknesses of arteries of the same size are significantly thicker in PH than in the controls. This statement is based on purely quantitative analysis and has to be completed by qualitative assessment of the vasculature by considering the level of the accompanying airways. Our investigation showed that in PH, muscular arteries extend to more distal airway levels and that smaller arteries are muscularized. In the normal fetal lung no muscular arteries are seen within the acinus (1 1, 13). Our study confirms this finding for gestational ages between the 17th and 40th gestational weeks. By contrast, in PH, muscular arteries extend peripherally to the intra-acinar level. One possible explanation for this finding is that, in contrast to the reduced development of lung parenchyma, normal growth of
60.
Hypoplasla
40.
20.
0
0
-0
0
;
'controls
O
d
20.
0
D O L
eo
0
Hypopl88la
60.
0
40 D
Controls
20.
20
I
I 16
20
26
30 36 Gestetlonal w e k
40
Hypoplasla
-
0
-
d 0
Q
1 15
0
L
26
25
30 Gestatlonal week
35
40
FIGURE 6. Synopsis of the vessel parameters R M T (upper row) and external radius (lower row) of intraacinar arteries (right column) and arteries accompanied by a terminal bronchiole (left column). For each case mean R M T and mean external radius were computed for the different types of related airways. Linear curve fit, confidence limits not displayed. (0) Controls; (0)PH group.
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
662
P. J. EARTH AND J. RUSCHOFF
-
-
FIGURE 7. Microphotograph of an intra-acinar muscular artery in pulmonary hypoplasia. The vessel is surrounded by a cuff of dense connective tissue. R M T 2 3 . 3 % , external radius 32 p n . Microscopic magnification X 460.
arterial smooth muscle takes place in P H , leading to a relative excess of vascular smooth muscle mass. This excess of arterial smooth muscle results in elevated R M T of arteries and extension of musculature to more distal airways, not muscularized during normal lung development. The correlation between RAC and AMT (Fig. 5) supports this hypothesis; with rising RAG, which reflects the development of lung parenchyma, the relative volume of smooth musculature per vessel, measured as AMT, decreases. Our data concerning the RAC values in normal fetal lungs are similar to those already published. RAC values for lung hypoplasia differ slightly from those published by Hislop et al. (7), who reported RAC ranging from 2.5 to 3.5 for bilateral poly- or multicystic renal dysplasia (38-41 weeks of gestation). In contrast, Reale and Esterly (1) found RAC values ranging from 2.3 to 7.8 (gestational age 32-44 weeks) in infants with polycystic bilateral renal dysplasia. In oligohydramnios the alveolar-intra-amniotic pressure gradient is elevated because of decreased amniotic pressure (18). This leads to loss of lung fluid, thought to be an essential cause in the development of PH. Based on this pathogenetic concept, in order to prevent P H oligohydramnios should be corrected by intrauterine instillation of artificial amniotic fluid (18). One case (37 weeks gestation, A M T 22.576, RAC 2.2) of cystic kidney disease submitted to
ARTERIES IN PULMONARY HYPOPLASIA
663
this therapy was examined in this study; no significant difference between the AMT and RAC values of the PH group was found.
Fetal Pediatr Pathol Downloaded from informahealthcare.com by University of Newcastle on 01/06/15 For personal use only.
REFERENCES 1. Reale FR, Esterly JR. Pulmonary hypoplasia: A morphometric study of the lungs of infants with diaphragmatic hernia, anencephaly, and renal malformations. Pediatrics 1973;51:91-6. 2 . Cooney TP, Thurlbeck WM. The radial alveolar count method of Emery and Mithal: A reappraisal. 1-Postnatal lung growth. Thorax 1982;37:572-9. 3. Cooney TP, Thurlbeck WM. The radial alveolar count method of Emery and Mithal: A reappraisal. 2-Intrauterine and early postnatal lung growth. Thorax 1982;37:580-3. 4. Itoh K , Suzuki J , Sakuragi K , et al. Clinicopathological studies on pulmonary hypoplasia in very low birth weight infants. Acta Pathol Jpn 1987;37:725-36. 5. Itoh K, Itoh H. A study of cartilage development in pulmonary hypoplasia. Pediatr Pathol 1988;8:6581. (Published erratum in Pediatr Pathol 1990;10:479.) 6. George DK, Cooney TP, Chiu BK, Thurlbeck W M . Hypoplasia and immaturity of the terminal lung unit (acinus) in congenital diaphragmatic hernia. Am Rev Respir Dis 1987;136:947-50. 7. Hislop A, Hey E, Reid L. The lungs in congenital bilateral renal agenesis and dysplasia. Arch Dis Child 1979;54:32-8. 8. Potter EL. Bilateral absence of ureters and kidneys: A report of 50 cases. Obstet Gynecol 1965;25:312. 9. Potter EL. Bilateral renal agenesis. J Pediatr 1946;29:68-76. 10. Wigglesworth JS, Desai R , Guerrini P. Fetal lung hypoplasia: Biochemical and structural variations and their possible significance. Arch Dis Child 56;1981:606-15. 11. Davies G, Reid L. Growth of the alveoli and pulmonary arteries in childhood. Thorax 1970;25:66981.
12. Heath D , Edwards JE. The pathology of hypertensive pulmonary vascular disease. A description of six grades of structural changes in the pulmonary arteries with special reference to congenital cardiac septal defects. Circulation 1958;18:533-47. 13. Hislop A, Reid L. Pulmonary arterial development during childhood: Branching pattern and structure. Thorax 1973;28:129-35. 14. Hislop A, Reid L. Intra-pulmonary arterial development during fetal life-Branching pattern and structure. J Anat 1972;113:35-48. 15. Cook TA, Yates PO. A critical survey of techniques for arterial mensuration. J Pathol 1972;108:11927. 16. Fernie J M , Lamb D. New method for measuring intimal component of pulmonary arteries. J Clin Pathol 1985;38:1374-9. 17. Fernie J M , Lamb D. Method for maximising measurements of muscular pulmonary arteries. J Clin Pathol 1985;38:1380-7. 18. Nicolini U, Fisk N M , Rodeck C H , Talbert DG, Wigglesworth JS. Low amniotic pressure in oligohydramnios-Is this the cause of pulmonary hypoplasia? Am J Obstet Gynecol 1989;161:1098101. 19. Thomas IT, Smith DW. Oligohydramnios, cause of the nonrenal features of Potter’s syndrome, including pulmonary hypoplasia. J Pediatr 1974;84:811-4. 20. Emery JL, Mithal A. The number of alveoli in the terminal respiratory unit of man during late intrauterine life and childhood. Arch Dis Child 1960;35:544-7. Received October 25, 1991 Revision accepted March 23, 1992
