Cardiothoracic Ratio in Newborns with Severe Intrauterine Growth Retardation Daniel G. Batton, M.D.* Connie Roberts, R.N., N.N.P. Alexander Cacciarelli, M.D.** *
Methods
Introduction n
t
newborns, the cardiothoracic
(CT)
ratio is used to
diagnose
if presdisease. ent, suggests Bozynski et all have reported that
cardiomegaly, which, cardiac
infants with intrauterine growth retardation (IUGR) often have elevated CT ratios without other evidence of cardiac disease. This limits the usefulness of the CT ratio in this population. Bozynski et al’ compared IUGR infants with infants whose birth weights were appropriate for gestational age (AGA) but who were considerably heavier (1,401 g vs 1,161 g) and younger (30.8 weeks vs 33.3 weeks) than the IUGR infants. However, Edwards et all reported that birth weight and gestational age are both directly related to the CT ratio. Therefore, we conducted a case-control retrospective study comparing the CT ratio in infants who have severe IUGR with two control groups: one matched closely for birth weight and another matched for gestational age.
* Department of Pediatrics Department of Radiology
**
William Beaumont
Hospital Royal Oak, Michigan
Address correspondence to: Daniel G. Batton, M.D., William Beaumont Hospital, 3601 West Thirteen Mile Road, Royal Oak, MI 48073-6769
(313) 551-0482
564
We identified all infants admitted to our neonatal intensive care unit (NICU) from January 1989 through December 1990 who had severe IUGR, defined as a birth weight less than two standard deviations from the mean (Suffield curves),3 and whose estimated gestational age was equal to or less than 32 weeks. Gestational age of the infant was determined from the first day of the mother’s last menstrual period and was revised by prenatal ultrasound or physical examination criteria if appropriate. Infants were excluded if they had evidence of structural or functional congenital heart disease or if they had not had an anterior-posterior chest radiograph within 24 hours of delivery. Birth-weight controls were matched for sex and birth weight within 100 g. Gestational-age controls were matched for sex and the number of completed weeks of gestation. Control infants also needed to have a chest radiograph done within 24 hours of delivery and be free of structural or functional heart disease. The radiographs were taken in the NICU with the infant in a supine position. The radiographs were reviewed by a single radiologist who was unaware of the infants’ clinical status or growth data. The CT ratio was determined by dividing the largest width of the cardiac silhouette by the largest in-
ternal width of the bony thorax. Statistical analyses were performed using the Fischer’s exact test for categorical data and Student’s t-test for continuous data.
Results Each group included 16 patients. The clinical data for these infants are listed in Table 1. The only significant differences between IUGR and control infants for these characteristics were those expected for birth weight and gestational age in the respective control groups. The mean CT ratio for the IUGR infants (0.60 ± 0.06) was considerably greater than for the birth-weight controls (0.51 ± 0.03; p < .001 ) and gestational-age controls (0.53 ± 0.05; p .0019). Ten of 16 IUGR infants had a CT ratio greater than 0.57 (Edwards upper limits of normal),2 but only two gestational-age and no birthweight control infants had CT ratios higher than that (Table 2). =
Discussion An elevated CT ratio, as determined from a chest radiograph, often suggests the presence of cardiac disease and may prompt further evaluation. However, none of the infants with an elevated CT ratio in this study had any clinical evidence of heart disease. Our
Downloaded from cpj.sagepub.com at NANYANG TECH UNIV LIBRARY on June 14, 2015
! DATA F~~ ’THE: THREE, GROUPS. ~~ ’
~
~
for the increased CT ratio in IUGR infants compared with birth-weight controls. The average gestational age of our birth-weight controls was 25 weeks, which corresponds to a mean heart weight of approximately 5.6 g.6 The average gestational age of the IUGR infants was 28 weeks, and the mean heart size of AGA infants at this gestational age is approximately 7.6 g.6 However, if we can expect a 30% to 40% reduction in heart size because of IUGR, 4,5 then the average heart size in our growth-retarded infants should be approximately 4.9 g, which is smaller than the estimated heart size in the birth-weight controls. Thus, the elevated CT ratio most likely is due to a decreased chest width in the IUGR infants. Whatever the mechanism, IUGR infants have an elevated CT ratio on chest radiograph when compared with either gestational-
probable explanation
:~~~MS~~~~/~~B
Table!i
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used cautiously making the diagnosis of cardiomegaly in these infants. before
REFERENCES 1.
Bozynski MEA, Hanafy FH, Hernandez RJ. Association of increased cardiothoracic ratio and intrauterine growth retardation.
2.
3.
study therefore agrees with that of Bozynski et all and demonstrates that an elevated CT ratio in IUGR infants must be interpreted cautiously and does not necessarily suggest heart disease. The elevated CT ratio might represent either a greater width of the cardiac silhouette or a smaller chest width. Human studies’ and experimental studies in rhesus monkeyS5 have indicated that IUGR fetuses
have a reduction in heart size that is proportional to the reduction in birth weight. In fact, heart size may be only 60% to 70% of that of gestational-age controls.4~5 This strongly suggests that the elevated CT ratio on chest radiograph in an IUGR infant compared with gestational-age matched controls is due to decreased thoracic size rather than increased heart size. A smaller chest cavity is also the
4. 5.
Am J Perinatol. 1991;8:28-30. Edwards DK, Higgins CB, Gilpin
EA. The cardiothoracic ratio in newborn infants. AJR. 1991;136:907-913. Keen DV, Pearse RG. Weight, length, and head circumference curves for boys and girls of between 20 and 42 weeks’ gestation. Arch Dis Child.
1988;63:1170-1172. Naeye RL. Malnutrition. Arch Pathol. 1965;79:284-291. Myers RE, Hill DE, Holt AB, et al. Fetal growth retardation produced by experimental placental insufficiency in the rhesus Biol Neonate. monkey. 1971;18:379-394.
6.
Gruenwald P, Minh HN. Evaluation of body and organ weight in perinatal pathology. Am J Clin Pathol.
1960;34:247-253.
Downloaded from cpj.sagepub.com at NANYANG TECH UNIV LIBRARY on June 14, 2015
565
Methods
Introduction n
t
newborns, the cardiothoracic
(CT)
ratio is used to
diagnose
if presdisease. ent, suggests Bozynski et all have reported that
cardiomegaly, which, cardiac
infants with intrauterine growth retardation (IUGR) often have elevated CT ratios without other evidence of cardiac disease. This limits the usefulness of the CT ratio in this population. Bozynski et al’ compared IUGR infants with infants whose birth weights were appropriate for gestational age (AGA) but who were considerably heavier (1,401 g vs 1,161 g) and younger (30.8 weeks vs 33.3 weeks) than the IUGR infants. However, Edwards et all reported that birth weight and gestational age are both directly related to the CT ratio. Therefore, we conducted a case-control retrospective study comparing the CT ratio in infants who have severe IUGR with two control groups: one matched closely for birth weight and another matched for gestational age.
* Department of Pediatrics Department of Radiology
**
William Beaumont
Hospital Royal Oak, Michigan
Address correspondence to: Daniel G. Batton, M.D., William Beaumont Hospital, 3601 West Thirteen Mile Road, Royal Oak, MI 48073-6769
(313) 551-0482
564
We identified all infants admitted to our neonatal intensive care unit (NICU) from January 1989 through December 1990 who had severe IUGR, defined as a birth weight less than two standard deviations from the mean (Suffield curves),3 and whose estimated gestational age was equal to or less than 32 weeks. Gestational age of the infant was determined from the first day of the mother’s last menstrual period and was revised by prenatal ultrasound or physical examination criteria if appropriate. Infants were excluded if they had evidence of structural or functional congenital heart disease or if they had not had an anterior-posterior chest radiograph within 24 hours of delivery. Birth-weight controls were matched for sex and birth weight within 100 g. Gestational-age controls were matched for sex and the number of completed weeks of gestation. Control infants also needed to have a chest radiograph done within 24 hours of delivery and be free of structural or functional heart disease. The radiographs were taken in the NICU with the infant in a supine position. The radiographs were reviewed by a single radiologist who was unaware of the infants’ clinical status or growth data. The CT ratio was determined by dividing the largest width of the cardiac silhouette by the largest in-
ternal width of the bony thorax. Statistical analyses were performed using the Fischer’s exact test for categorical data and Student’s t-test for continuous data.
Results Each group included 16 patients. The clinical data for these infants are listed in Table 1. The only significant differences between IUGR and control infants for these characteristics were those expected for birth weight and gestational age in the respective control groups. The mean CT ratio for the IUGR infants (0.60 ± 0.06) was considerably greater than for the birth-weight controls (0.51 ± 0.03; p < .001 ) and gestational-age controls (0.53 ± 0.05; p .0019). Ten of 16 IUGR infants had a CT ratio greater than 0.57 (Edwards upper limits of normal),2 but only two gestational-age and no birthweight control infants had CT ratios higher than that (Table 2). =
Discussion An elevated CT ratio, as determined from a chest radiograph, often suggests the presence of cardiac disease and may prompt further evaluation. However, none of the infants with an elevated CT ratio in this study had any clinical evidence of heart disease. Our
Downloaded from cpj.sagepub.com at NANYANG TECH UNIV LIBRARY on June 14, 2015
! DATA F~~ ’THE: THREE, GROUPS. ~~ ’
~
~
for the increased CT ratio in IUGR infants compared with birth-weight controls. The average gestational age of our birth-weight controls was 25 weeks, which corresponds to a mean heart weight of approximately 5.6 g.6 The average gestational age of the IUGR infants was 28 weeks, and the mean heart size of AGA infants at this gestational age is approximately 7.6 g.6 However, if we can expect a 30% to 40% reduction in heart size because of IUGR, 4,5 then the average heart size in our growth-retarded infants should be approximately 4.9 g, which is smaller than the estimated heart size in the birth-weight controls. Thus, the elevated CT ratio most likely is due to a decreased chest width in the IUGR infants. Whatever the mechanism, IUGR infants have an elevated CT ratio on chest radiograph when compared with either gestational-
probable explanation
:~~~MS~~~~/~~B
Table!i
STUDIED ~~F:~~T~ ~T~~~~~
&dquo;
agex
~Y ~e ,x~
© ’
~
&dquo;i~· &dquo;:,. a :
~~i~$1~ ;$: ’ ..#&dquo; _ ;~ ~
j_ _ (
&dquo; ’ .
*:.
##~’=.»
’
lo
used cautiously making the diagnosis of cardiomegaly in these infants. before
REFERENCES 1.
Bozynski MEA, Hanafy FH, Hernandez RJ. Association of increased cardiothoracic ratio and intrauterine growth retardation.
2.
3.
study therefore agrees with that of Bozynski et all and demonstrates that an elevated CT ratio in IUGR infants must be interpreted cautiously and does not necessarily suggest heart disease. The elevated CT ratio might represent either a greater width of the cardiac silhouette or a smaller chest width. Human studies’ and experimental studies in rhesus monkeyS5 have indicated that IUGR fetuses
have a reduction in heart size that is proportional to the reduction in birth weight. In fact, heart size may be only 60% to 70% of that of gestational-age controls.4~5 This strongly suggests that the elevated CT ratio on chest radiograph in an IUGR infant compared with gestational-age matched controls is due to decreased thoracic size rather than increased heart size. A smaller chest cavity is also the
4. 5.
Am J Perinatol. 1991;8:28-30. Edwards DK, Higgins CB, Gilpin
EA. The cardiothoracic ratio in newborn infants. AJR. 1991;136:907-913. Keen DV, Pearse RG. Weight, length, and head circumference curves for boys and girls of between 20 and 42 weeks’ gestation. Arch Dis Child.
1988;63:1170-1172. Naeye RL. Malnutrition. Arch Pathol. 1965;79:284-291. Myers RE, Hill DE, Holt AB, et al. Fetal growth retardation produced by experimental placental insufficiency in the rhesus Biol Neonate. monkey. 1971;18:379-394.
6.
Gruenwald P, Minh HN. Evaluation of body and organ weight in perinatal pathology. Am J Clin Pathol.
1960;34:247-253.
Downloaded from cpj.sagepub.com at NANYANG TECH UNIV LIBRARY on June 14, 2015
565
