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Small thymus in very low birth weight infants born to mothers with subclinical chorioamnionitis
S
Small thymus in very low birth weight infants born
to mothers with subclinical chorioamnionitis Claudio De Felice, MD, Paolo Toti, MD, Rosa Santopietro, MD, Michela Stumpo, MD, Lorenza Pecciarini, MD, and Franco Bagnoli, MD Thymic Size Assessment Chorioamnionitis, a major cause of preterm birth with significant neonatal morbidity and mortality, frequently occurs in mothers who are free of symptoms. A combined clinical, radiologic, and pathologic study of 129 very low birth weight infants indicated a significant association between a markedly decreased thymic size at birth and subclinical chorioamnionitis. (J Pediatr 1999;135:384-6)
Chorioamnionitis is a major cause of preterm birth.1 Cumulative evidence indicates that CA is associated with a severe multisystem disease in the fetus,2,3 leading to high morbidity and mortality rates in newborns.4 CA frequently occurs in the absence of clinical signs in the mother and may remain undiagnosed unless an accurate placental histologic examination is performed.4 The thymus may shrink after inflammatory processes or other conditions of distress.5 Because the thymus is easily recognizable on a chest radiograph
From the Department of Preventive Pediatrics and Neonatology, the Institute of Pathology, and the Department of Obstetrics and Gynecology, University of Siena, Italy.
Supported by a grant from the Italian Ministry of Education MURST (funding for Research of National Interest) and by a grant from the University of Siena. Submitted for publication Feb 2, 1999; revision received Apr 28, 1999; accepted May 12, 1999. Reprint requests: Claudio De Felice, MD, Istituto di Pediatria Preventiva e Neonatologia, Azienda Ospedaliera Senese, Viale M. Bracci, I-53100 Siena, Italy. Copyright © 1999 by Mosby, Inc. 0022-3476/99/$8.00 + 0 9/22/100098
384
at birth, we determined whether a significant decrease in thymic size in very low birth weight preterm neonates is related to subclinical CA.
METHODS Patients Clinical data, radiologic thymic size, and placental histologic findings were examined for 129 VLBW infants who were born in the hospital and admitted to the neonatal intensive care unit (73 boys and 56 girls; gestational age [mean ± SD]: 26.9 ± 1.8 weeks; range, 23.3-30.6 weeks; birth weight, 969 ± 269 g; range, 460-1490 g). Infants born to mothers with symptomatic intrauterine infection, gestational diabetes, hypertension before pregnancy, polyhydramnios, uterine malformations, placenta previa, or abruptio placentae and infants born to mothers who had undergone cervical cerclage were excluded. None of the infants had major malformations, primary immunodeficiency disorders, or mediastinal diseases. Clinical severity in the first 24 hours after birth was assessed by using the Score for Neonatal Acute Physiology–Perinatal Extension.6 Data collection was performed prospectively.
The width of the cardiothymic silhouette was measured at the level of the carina in routine, anteroposterior supine chest radiographs, taken in the first 6 hours after birth (median, 2 hours; range, 0.2-6 hours). Thymic size was expressed as the ratio between the transverse diameter of the cardiothymic image and that of the thorax7 (Figure). A standard portable, capacitor-discharge–type neonatal radiographic unit (Kondiamobil 125, Siemens) was used. CA Chorioamnionitis CT/T Cardiothymic to thoracic ratio VLBW Very low birth weight
Placental Examination Placental histologic examination and neonatal autopsies were performed as previously described.3 A diagnosis of histologic CA was made, given the presence of at least 10 polymorphonuclear leukocytes per field in 10 nonadjacent 400-power fields. Pathologists were unaware of the neonatal clinical findings.
Statistical Analysis Differences between variables were tested with the Student t test for unpaired data, the Mann-Whitney U test, or Fisher exact test, as appropriate. A receiver operating characteristic curve was used to describe the relationship between sensitivity and the false-positive rate for different values of CT/T in the prediction of histologic CA. Posttest probabilities of CA, given the presence or absence of a small thymus,
DE FELICE ET AL
THE JOURNAL OF PEDIATRICS VOLUME 135, NUMBER 3 Table. Comparisons between VLBW infants with a small thymus in the chest radiograph (CT/T ≤ 0.26) and control subjects (CT/T > 0.26): relevant maternal, prenatal, and neonatal characteristics
Small thymus (n = 73) Sex (M:F) Vaginal delivery Gestational age (wk) Birth weight (g) Pregnancy-induced hypertension pPROM IUGR Fetal distress Antenatal steroids Birth asphyxia Histologic chorioamnionitis SNAP-PE
40:33 50 (68.5%) 26.8 ± 1.7 907 ± 262 11 (15.1%) 15 (20.5%) 8 (10.9%) 42 (57.5%) 23 (31.5%) 34 (46.6%) 68 (93.1%) 49.7 ± 27.1
Normal thymus (n = 56) 33:23 21 (37.5%)* 27.7 ± 1.6 1023 ± 255† 14 (25%) 9 (16.1%) 5 (8.9%) 30 (53.4%) 14 (25%) 25 (44.6%) 7 (12.5%)‡ 29.1 ± 3.5*
Continuous variables are expressed as mean ± SD. Categoric variables are expressed as number of cases with percentages in parentheses. Asphyxia was defined as a pH value <7.1 and base deficit < –7 mmol/L in umbilical vein blood at birth. pPROM, Preterm premature rupture of the membranes; IUGR, intrauterine growth retardation; SNAP-PE, Score for Neonatal Acute Physiology–Perinatal Extension. *P < .01. †P < .05. ‡P < .001.
were calculated by using Bayes’ theorem. The relationship between decreased thymic size and CA was examined by using logistic regression analysis. A 2-tailed P value of <.05 was considered statistically significant.
RESULTS Histologic CA was found for 75 (58%) of the infants (43 boys and 32 girls), and no placental inflammation was evident for 54 (42%) neonates (31 boys and 23 girls). CT/T was significantly lower in newborns with CA (median, 0.21; 25%-75% value, 0.180.24) compared with control subjects (median, 0.34; 25%-75% value, 0.290.39) (P < .001). A CT/T ≤0.26 by receiver operating characteristic curve analysis identified infants who had CA with a sensitivity (true positive ratio) of 91% and specificity (true negative ratio) of 91% (positive and negative likelihood ratios of 9.79 and 0.103, respectively).
Post-test probability of histologic CA was 0.92 in the presence of significantly decreased thymic size (CT/T ≤0.26) and 0.10 with normal thymus appearance (CT/T >0.26). A small thymus was also associated with lower birth weight, higher frequency of vaginal delivery, increased morbidity, and a higher mortality rate, compared with an apparently normal thymus. Conversely, no significant differences in other relevant maternal, prenatal, or neonatal features were present (Table). Multivariate logistic regression analysis showed a significant positive correlation between small thymus and histologic CA after adjustment for mode of delivery, birth weight, Score for Neonatal Acute Physiology–Perinatal Extension, and neonatal mortality rate (adjusted odds ratio, 9.38; 95% CI, 4.7-18.6; P < .001). Infant death occurred in 27 cases of CA and in 5 cases without placental inflammatory changes (P < .001), with no significant differences in gender distribution, gestational age, birth
Figure. CT/T in VLBW preterm infants, measured on portable anteroposterior chest radiographs by expressing width of cardiothymic image at the level of the carina as a function of transverse diameter of the thorax at the level of the costophrenic angles.7 A, Subclinical histologic CA (CT/T = 0.20); B, Control, (CT/T = 0.35). weight, or age at death between the 2 groups. Of the 27 cases of CA, the cause of death was sepsis in 7, multiorgan failure in 5, pulmonary hemorrhage in 5, massive intraventricular hemorrhage in 5, severe respiratory distress syndrome in 3, and severe pneumonia in 2. Among the control subjects, the cause of death was pulmonary hemorrhage in 2, severe respiratory distress syndrome in 2, and multi-organ failure in one. The small thymic size corresponded to histologic findings of significant thymic lymphocyte depletion involving both the cortex and medulla. Conversely, lymphocyte depletion was not observed in the thymuses of infants without CA.
DISCUSSION The results of this study indicate that histologic CA is associated with a significant decrease in thymic size at birth in VLBW preterm infants, which corresponds to histologic findings of acute 385
DE FELICE ET AL
thymic involution. Although the conventional chest x-ray film is an imperfect means of measuring thymus size, it is the most common neonatal imaging procedure and was effective in distinguishing between infants born to mothers with CA and the control subjects. Involution of the thymus is known to occur as a nonspecific, steroid-mediated response to infection or other acute stress.5 However, its underlying mechanisms and significance remain unclear. Even in the absence of demonstrable neonatal or maternal infection, histologic CA is known to be associated with biochemical changes during pregnancy, including: (1) increased production of cytokines (IL-1α, IL-1β, tumor necrosis factor-α, granulocyte–colony-stimulating factor, IL-6, and IL-8)8; (2) increased release of free radicals from monocytes and neutrophils9; and (3) induction of nitric oxide synthase in the fetal amnion.10 Cumulative evidence indicates that the stress-related activation of the hypothalamo-pituitary-adrenal axis can be mediated by proinflammatory cytokines (ie, IL-1β, IL-6) and products of activated macrophages. A dramatic thymic lymphocyte depletion after exposure to IL-1α and IL1β in mice has been reported,11 and the administration of IL-1β to pregnant rats has been shown to activate the hypothalamo-pituitary-adrenal axis in the mother and reduce thymic weights
386
THE JOURNAL OF PEDIATRICS SEPTEMBER 1999 in both the mother and fetus.12 It is therefore conceivable that even in the absence of neonatal infection, inflammatory mediators generated at the feto-maternal interface during CA may activate either the maternal or fetal hypothalamo-pituitary-adrenal axis, leading to the observed thymic changes in the infants. Our findings confirm prior reports on the presence of a significant fetal inflammatory response in CA.2 In addition, we have demonstrated that through detection of a small thymus, a standard chest x-ray film may be used to identify a new category of high-risk preterm neonates who require close clinical monitoring in order to prevent associated morbidity and mortality.
6.
7.
8.
9.
REFERENCES 1. Mercer BM, Lewis R. Preterm labor and preterm premature rupture of the membranes. Infect Dis Clin North Am 1997;11:177-201. 2. Gomez R, Romero R, Ghezzi F, Yoon H, Mazor M, Berry SM. The fetal inflammatory response syndrome. Am J Obstet Gynecol 1998;179:194-202. 3. Toti P, De Felice C, Palmeri MLD, Villanova M, Martin JJ, Buonocore G. Inflammatory pathogenesis of cortical polymicrogyria: an autopsy study. Pediatr Res 1998;44:291-6. 4. Altshuler G. The role of the placenta in perinatal pathology (revisited). Pediatr Pathol Lab Med 1996;16:207-33. 5. Mueller-Hermelink HK, Marx A,
10.
11.
12.
Kirchner T. Thymus. In: Damianov I, Linder J, editors. Anderson’s pathology. St Louis: Mosby; 1996. p. 1218-43. Richardson DK, Gray JE, McCormick MC, Workman K, Goldmann DA. Score for Neonatal Acute Physiology: a physiologic severity index for neonatal intensive care. Pediatrics 1993;91:617-23. Fletcher BD, Masson M, Lisbona A, Riggs T, Papageorgiou AN. Thymic response to endogenous and exogenous steroids in premature newborn infants. J Pediatr 1979;95:111-4. Stallmach T, Hebisch G, Joller-Jemelka HI, Orban P, Schwaller J, Engelmann M. Cytokine production and visualized effects in the feto-maternal unit. Quantitative and topographic data on cytokines during intrauterine disease. Lab Invest 1995;73:384-92. Okada T, Matzusaki N, Sawai K, Nobunaga T, Shimoya K, Suzuki K, et al. Chorioamnionitis reduces placental endocrine functions: the role of bacterial lipopolysaccharide and superoxide anion. J Endocrinol 1997;155:401-10. Hsu C-D, Meaddough E, Lu L-C, Chelouche A, Liang R-I, Copel JA, et al. Immunohistochemical localization of inducible nitric oxide synthase on human fetal amnion in intra-amniotic infection. Am J Obstet Gynecol 1998; 179:1271-4. Morrissey PJ, Charrier K, Alpert A, Bressler L. In vivo administration of IL-1 induces thymic hypoplasia and increased levels of serum corticosterone. J Immunol 1988;141:1456-63. Götz F, Dörner G, Malz U, Rohde W, Stahl F, Poppe I, et al. Short- and longterm effects of perinatal interleukin-1β application in rats. Neuroendocrinology 1993;58:344-51.
Small thymus in very low birth weight infants born
to mothers with subclinical chorioamnionitis Claudio De Felice, MD, Paolo Toti, MD, Rosa Santopietro, MD, Michela Stumpo, MD, Lorenza Pecciarini, MD, and Franco Bagnoli, MD Thymic Size Assessment Chorioamnionitis, a major cause of preterm birth with significant neonatal morbidity and mortality, frequently occurs in mothers who are free of symptoms. A combined clinical, radiologic, and pathologic study of 129 very low birth weight infants indicated a significant association between a markedly decreased thymic size at birth and subclinical chorioamnionitis. (J Pediatr 1999;135:384-6)
Chorioamnionitis is a major cause of preterm birth.1 Cumulative evidence indicates that CA is associated with a severe multisystem disease in the fetus,2,3 leading to high morbidity and mortality rates in newborns.4 CA frequently occurs in the absence of clinical signs in the mother and may remain undiagnosed unless an accurate placental histologic examination is performed.4 The thymus may shrink after inflammatory processes or other conditions of distress.5 Because the thymus is easily recognizable on a chest radiograph
From the Department of Preventive Pediatrics and Neonatology, the Institute of Pathology, and the Department of Obstetrics and Gynecology, University of Siena, Italy.
Supported by a grant from the Italian Ministry of Education MURST (funding for Research of National Interest) and by a grant from the University of Siena. Submitted for publication Feb 2, 1999; revision received Apr 28, 1999; accepted May 12, 1999. Reprint requests: Claudio De Felice, MD, Istituto di Pediatria Preventiva e Neonatologia, Azienda Ospedaliera Senese, Viale M. Bracci, I-53100 Siena, Italy. Copyright © 1999 by Mosby, Inc. 0022-3476/99/$8.00 + 0 9/22/100098
384
at birth, we determined whether a significant decrease in thymic size in very low birth weight preterm neonates is related to subclinical CA.
METHODS Patients Clinical data, radiologic thymic size, and placental histologic findings were examined for 129 VLBW infants who were born in the hospital and admitted to the neonatal intensive care unit (73 boys and 56 girls; gestational age [mean ± SD]: 26.9 ± 1.8 weeks; range, 23.3-30.6 weeks; birth weight, 969 ± 269 g; range, 460-1490 g). Infants born to mothers with symptomatic intrauterine infection, gestational diabetes, hypertension before pregnancy, polyhydramnios, uterine malformations, placenta previa, or abruptio placentae and infants born to mothers who had undergone cervical cerclage were excluded. None of the infants had major malformations, primary immunodeficiency disorders, or mediastinal diseases. Clinical severity in the first 24 hours after birth was assessed by using the Score for Neonatal Acute Physiology–Perinatal Extension.6 Data collection was performed prospectively.
The width of the cardiothymic silhouette was measured at the level of the carina in routine, anteroposterior supine chest radiographs, taken in the first 6 hours after birth (median, 2 hours; range, 0.2-6 hours). Thymic size was expressed as the ratio between the transverse diameter of the cardiothymic image and that of the thorax7 (Figure). A standard portable, capacitor-discharge–type neonatal radiographic unit (Kondiamobil 125, Siemens) was used. CA Chorioamnionitis CT/T Cardiothymic to thoracic ratio VLBW Very low birth weight
Placental Examination Placental histologic examination and neonatal autopsies were performed as previously described.3 A diagnosis of histologic CA was made, given the presence of at least 10 polymorphonuclear leukocytes per field in 10 nonadjacent 400-power fields. Pathologists were unaware of the neonatal clinical findings.
Statistical Analysis Differences between variables were tested with the Student t test for unpaired data, the Mann-Whitney U test, or Fisher exact test, as appropriate. A receiver operating characteristic curve was used to describe the relationship between sensitivity and the false-positive rate for different values of CT/T in the prediction of histologic CA. Posttest probabilities of CA, given the presence or absence of a small thymus,
DE FELICE ET AL
THE JOURNAL OF PEDIATRICS VOLUME 135, NUMBER 3 Table. Comparisons between VLBW infants with a small thymus in the chest radiograph (CT/T ≤ 0.26) and control subjects (CT/T > 0.26): relevant maternal, prenatal, and neonatal characteristics
Small thymus (n = 73) Sex (M:F) Vaginal delivery Gestational age (wk) Birth weight (g) Pregnancy-induced hypertension pPROM IUGR Fetal distress Antenatal steroids Birth asphyxia Histologic chorioamnionitis SNAP-PE
40:33 50 (68.5%) 26.8 ± 1.7 907 ± 262 11 (15.1%) 15 (20.5%) 8 (10.9%) 42 (57.5%) 23 (31.5%) 34 (46.6%) 68 (93.1%) 49.7 ± 27.1
Normal thymus (n = 56) 33:23 21 (37.5%)* 27.7 ± 1.6 1023 ± 255† 14 (25%) 9 (16.1%) 5 (8.9%) 30 (53.4%) 14 (25%) 25 (44.6%) 7 (12.5%)‡ 29.1 ± 3.5*
Continuous variables are expressed as mean ± SD. Categoric variables are expressed as number of cases with percentages in parentheses. Asphyxia was defined as a pH value <7.1 and base deficit < –7 mmol/L in umbilical vein blood at birth. pPROM, Preterm premature rupture of the membranes; IUGR, intrauterine growth retardation; SNAP-PE, Score for Neonatal Acute Physiology–Perinatal Extension. *P < .01. †P < .05. ‡P < .001.
were calculated by using Bayes’ theorem. The relationship between decreased thymic size and CA was examined by using logistic regression analysis. A 2-tailed P value of <.05 was considered statistically significant.
RESULTS Histologic CA was found for 75 (58%) of the infants (43 boys and 32 girls), and no placental inflammation was evident for 54 (42%) neonates (31 boys and 23 girls). CT/T was significantly lower in newborns with CA (median, 0.21; 25%-75% value, 0.180.24) compared with control subjects (median, 0.34; 25%-75% value, 0.290.39) (P < .001). A CT/T ≤0.26 by receiver operating characteristic curve analysis identified infants who had CA with a sensitivity (true positive ratio) of 91% and specificity (true negative ratio) of 91% (positive and negative likelihood ratios of 9.79 and 0.103, respectively).
Post-test probability of histologic CA was 0.92 in the presence of significantly decreased thymic size (CT/T ≤0.26) and 0.10 with normal thymus appearance (CT/T >0.26). A small thymus was also associated with lower birth weight, higher frequency of vaginal delivery, increased morbidity, and a higher mortality rate, compared with an apparently normal thymus. Conversely, no significant differences in other relevant maternal, prenatal, or neonatal features were present (Table). Multivariate logistic regression analysis showed a significant positive correlation between small thymus and histologic CA after adjustment for mode of delivery, birth weight, Score for Neonatal Acute Physiology–Perinatal Extension, and neonatal mortality rate (adjusted odds ratio, 9.38; 95% CI, 4.7-18.6; P < .001). Infant death occurred in 27 cases of CA and in 5 cases without placental inflammatory changes (P < .001), with no significant differences in gender distribution, gestational age, birth
Figure. CT/T in VLBW preterm infants, measured on portable anteroposterior chest radiographs by expressing width of cardiothymic image at the level of the carina as a function of transverse diameter of the thorax at the level of the costophrenic angles.7 A, Subclinical histologic CA (CT/T = 0.20); B, Control, (CT/T = 0.35). weight, or age at death between the 2 groups. Of the 27 cases of CA, the cause of death was sepsis in 7, multiorgan failure in 5, pulmonary hemorrhage in 5, massive intraventricular hemorrhage in 5, severe respiratory distress syndrome in 3, and severe pneumonia in 2. Among the control subjects, the cause of death was pulmonary hemorrhage in 2, severe respiratory distress syndrome in 2, and multi-organ failure in one. The small thymic size corresponded to histologic findings of significant thymic lymphocyte depletion involving both the cortex and medulla. Conversely, lymphocyte depletion was not observed in the thymuses of infants without CA.
DISCUSSION The results of this study indicate that histologic CA is associated with a significant decrease in thymic size at birth in VLBW preterm infants, which corresponds to histologic findings of acute 385
DE FELICE ET AL
thymic involution. Although the conventional chest x-ray film is an imperfect means of measuring thymus size, it is the most common neonatal imaging procedure and was effective in distinguishing between infants born to mothers with CA and the control subjects. Involution of the thymus is known to occur as a nonspecific, steroid-mediated response to infection or other acute stress.5 However, its underlying mechanisms and significance remain unclear. Even in the absence of demonstrable neonatal or maternal infection, histologic CA is known to be associated with biochemical changes during pregnancy, including: (1) increased production of cytokines (IL-1α, IL-1β, tumor necrosis factor-α, granulocyte–colony-stimulating factor, IL-6, and IL-8)8; (2) increased release of free radicals from monocytes and neutrophils9; and (3) induction of nitric oxide synthase in the fetal amnion.10 Cumulative evidence indicates that the stress-related activation of the hypothalamo-pituitary-adrenal axis can be mediated by proinflammatory cytokines (ie, IL-1β, IL-6) and products of activated macrophages. A dramatic thymic lymphocyte depletion after exposure to IL-1α and IL1β in mice has been reported,11 and the administration of IL-1β to pregnant rats has been shown to activate the hypothalamo-pituitary-adrenal axis in the mother and reduce thymic weights
386
THE JOURNAL OF PEDIATRICS SEPTEMBER 1999 in both the mother and fetus.12 It is therefore conceivable that even in the absence of neonatal infection, inflammatory mediators generated at the feto-maternal interface during CA may activate either the maternal or fetal hypothalamo-pituitary-adrenal axis, leading to the observed thymic changes in the infants. Our findings confirm prior reports on the presence of a significant fetal inflammatory response in CA.2 In addition, we have demonstrated that through detection of a small thymus, a standard chest x-ray film may be used to identify a new category of high-risk preterm neonates who require close clinical monitoring in order to prevent associated morbidity and mortality.
6.
7.
8.
9.
REFERENCES 1. Mercer BM, Lewis R. Preterm labor and preterm premature rupture of the membranes. Infect Dis Clin North Am 1997;11:177-201. 2. Gomez R, Romero R, Ghezzi F, Yoon H, Mazor M, Berry SM. The fetal inflammatory response syndrome. Am J Obstet Gynecol 1998;179:194-202. 3. Toti P, De Felice C, Palmeri MLD, Villanova M, Martin JJ, Buonocore G. Inflammatory pathogenesis of cortical polymicrogyria: an autopsy study. Pediatr Res 1998;44:291-6. 4. Altshuler G. The role of the placenta in perinatal pathology (revisited). Pediatr Pathol Lab Med 1996;16:207-33. 5. Mueller-Hermelink HK, Marx A,
10.
11.
12.
Kirchner T. Thymus. In: Damianov I, Linder J, editors. Anderson’s pathology. St Louis: Mosby; 1996. p. 1218-43. Richardson DK, Gray JE, McCormick MC, Workman K, Goldmann DA. Score for Neonatal Acute Physiology: a physiologic severity index for neonatal intensive care. Pediatrics 1993;91:617-23. Fletcher BD, Masson M, Lisbona A, Riggs T, Papageorgiou AN. Thymic response to endogenous and exogenous steroids in premature newborn infants. J Pediatr 1979;95:111-4. Stallmach T, Hebisch G, Joller-Jemelka HI, Orban P, Schwaller J, Engelmann M. Cytokine production and visualized effects in the feto-maternal unit. Quantitative and topographic data on cytokines during intrauterine disease. Lab Invest 1995;73:384-92. Okada T, Matzusaki N, Sawai K, Nobunaga T, Shimoya K, Suzuki K, et al. Chorioamnionitis reduces placental endocrine functions: the role of bacterial lipopolysaccharide and superoxide anion. J Endocrinol 1997;155:401-10. Hsu C-D, Meaddough E, Lu L-C, Chelouche A, Liang R-I, Copel JA, et al. Immunohistochemical localization of inducible nitric oxide synthase on human fetal amnion in intra-amniotic infection. Am J Obstet Gynecol 1998; 179:1271-4. Morrissey PJ, Charrier K, Alpert A, Bressler L. In vivo administration of IL-1 induces thymic hypoplasia and increased levels of serum corticosterone. J Immunol 1988;141:1456-63. Götz F, Dörner G, Malz U, Rohde W, Stahl F, Poppe I, et al. Short- and longterm effects of perinatal interleukin-1β application in rats. Neuroendocrinology 1993;58:344-51.