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Chapter 39 ■ The Fetal Urogenital Tract 1387
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161. Gonzalez R, De Filippo R, Jednak R, Barthold JS. Urethral atresia:
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162. Jaramillo D, Lebowitz RL, Hendren WH. The cloacal malformation:
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163. Johnson MP, Corsi P, Bradfield W, et al. Sequential urinalysis
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164. Nicolini U, Fisk NM, Rodeck CH, Beacham J. Fetal urine biochemistry: an index of renal maturation and dysfunction. Br J Obstet
Gynaecol 1992;99:46-50.
165. Lipitz S, Ryan G, Samuell C, et al. Fetal urine analysis for the assessment of renal function in obstructive uropathy. Am J Obstet
Gynecol 1993;168:174-179.
166. Muller F, Dommergues M, Mandelbrot L, et al. Fetal urinary biochemistry predicts postnatal renal function in children with bilateral
obstructive uropathies. Obstet Gynecol 1993;82:813-820.
167. Crombleholme TM, Harrison MR, Golbus MS, et al. Fetal intervention in obstructive uropathy: prognostic indicators and efficacy of
intervention. Am J Obstet Gynecol 1990;162:1239-1244.
168. Qureshi F, Jacques SM, Seifman B, et al. In utero fetal urine analysis
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169. Muller F, Dommergues M, Bussieres L, et al. Development of
human renal function: reference intervals for 10 biochemical markers
in fetal urine. Clin Chem 1996;42:1855-1860.
170. Nicolaides KH, Cheng HH, Snijders RJ, Moniz CF. Fetal urine
biochemistry in the assessment of obstructive uropathy. Am J Obstet
Gynecol 1992;166:932-937.
171. Berry SM, Lecolier B, Smith RS, et al. Predictive value of fetal serum
beta 2-microglobulin for neonatal renal function. Lancet 1995;
345:1277-1278.
172. Nicolini U, Spelzini F. Invasive assessment of fetal renal abnormalities: urinalysis, fetal blood sampling and biopsy. Prenat Diagn
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173. Morris RK, Quinlan-Jones E, Kilby MD, Khan KS. Systematic
review of accuracy of fetal urine analysis to predict poor postnatal
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174. Holmes N, Harrison MR, Baskin LS. Fetal surgery for posterior
urethral valves: long-term postnatal outcomes. Pediatrics 2001;
108:E7.
175. Makino Y, Kobayashi H, Kyono K, et al. Clinical results of fetal
obstructive uropathy treated by vesicoamniotic shunting. Urology
2000;55:118-122.
176. McLorie G, Farhat W, Khoury A, et al. Outcome analysis of vesicoamniotic shunting in a comprehensive population. J Urol
2001;166:1036-1040.
177. Freedman AL, Johnson MP, Smith CA, et al. Long-term outcome
in children after antenatal intervention for obstructive uropathies.
Lancet 1999;354:374-377.
178. Clark TJ, Martin WL, Divakaran TG, et al. Prenatal bladder drainage in the management of fetal lower urinary tract obstruction:
a systematic review and meta-analysis. Obstet Gynecol 2003;102:
367-382.
179. Biard JM, Johnson MP, Carr MC, et al. Long-term outcomes in
children treated by prenatal vesicoamniotic shunting for lower
urinary tract obstruction. Obstet Gynecol 2005;106:503-508.
180. Gearhart JP, Ben-Chaim J, Jeffs RD, Sanders RC. Criteria for the
prenatal diagnosis of classic bladder exstrophy. Obstet Gynecol
1995;85:961-964.
181. Ben-Neriah Z, Withers S, Thomas M, et al. OEIS complex: prenatal
ultrasound and autopsy findings. Ultrasound Obstet Gynecol
2007;29:170-177.
182. Tiblad E, Wilson RD, Carr M, et al. OEIS sequence: a rare congenital anomaly with prenatal evaluation and postnatal outcome in
six cases. Prenat Diagn 2008;28:141-147.
The Genital Tract
183. Reece EA, Winn HN, Wan M, et al. Can ultrasonography replace
amniocentesis in fetal gender determination during the early second
trimester? Am J Obstet Gynecol 1987;156:579-581.
184. Harrington K, Armstrong V, Freeman J, et al. Fetal sexing by
ultrasound in the second trimester: maternal preference and professional ability [see comment]. Ultrasound Obstet Gynecol 1996;8:
318-321.
185. Meagher S, Davison G. Early second-trimester determination of
fetal gender by ultrasound [see comment]. Ultrasound Obstet
Gynecol 1996;8:322-324.
186. Lev-Toaff AS, Ozhan S, Pretorius D, et al. Three-dimensional
multiplanar ultrasound for fetal gender assignment: value of the
mid-sagittal plane. Ultrasound Obstet Gynecol 2000;16:345-350.
187. Whitlow BJ, Lazanakis MS, Economides DL. The sonographic
identification of fetal gender from 11 to 14 weeks of gestation [see
comment]. Ultrasound Obstet Gynecol 1999;13:301-304.
188. Efrat Z, Akinfenwa OO, Nicolaides KH. First-trimester determination of fetal gender by ultrasound [see comment]. Ultrasound Obstet
Gynecol 1999;13:305-307.
189. Mazza V, Falcinelli C, Paganelli S, et al. Sonographic early fetal
gender assignment: a longitudinal study in pregnancies after in vitro
fertilization. Ultrasound Obstet Gynecol 2001;17:513-516.
190. Achiron R, Pinhas-Hamiel O, Zalel Y, et al. Development of fetal
male gender: prenatal sonographic measurement of the scrotum and
evaluation of testicular descent [see comment]. Ultrasound Obstet
Gynecol 1998;11:242-245.
191. Pretorius DH, Halsted MJ, Abels W, et al. Hydroceles identified
prenatally: common physiologic phenomenon? J Ultrasound Med
1998;17:49-52.
192. Meizner I, Levy A, Katz M, et al. Prenatal ultrasonographic diagnosis
of fetal scrotal inguinal hernia. Am J Obstet Gynecol 1992;
166:907-909.
193. Mandell J, Bromley B, Peters CA, Benacerraf BR. Prenatal sonographic detection of genital malformations. J Urol 1995;153:
1994-1996.
194. Shapiro E. The sonographic appearance of normal and abnormal
fetal genitalia. J Urol 1999;162:530-533.
195. Cheikhelard A, Luton D, Philippe-Chomette P, et al. How accurate
is the prenatal diagnosis of abnormal genitalia? J Urol 2000;164:
984-987.
196. Meizner I. The “tulip sign”: a sonographic clue for in-utero
diagnosis of severe hypospadias. Ultrasound Obstet Gynecol
2002;19:317.
197. McGaughran JM, Clayton PT, Mills KA, et al. Prenatal diagnosis of
Smith-Lemli-Opitz syndrome. Am J Med Genet 1995;56:
269-271.
198. Shapiro E, Santiago JV, Crane JP. Prenatal fetal adrenal suppression
following in utero diagnosis of congenital adrenal hyperplasia. J Urol
1989;142:663-666; discussion 667-668.
199. Saada J, Grebille AG, Aubry MC, et al. Sonography in prenatal
diagnosis of congenital adrenal hyperplasia. Prenat Diagn 2004;
24:627-630.
200. Carlson AD, Obeid JS, Kanellopoulou N, et al. Congenital adrenal
hyperplasia: update on prenatal diagnosis and treatment. J Steroid
Biochem Mol Biol 1999;69:19-29.
201. New MI. An update of congenital adrenal hyperplasia. Ann NY
Acad Sci 2004;1038:14-43.
202. Pajkrt E, Petersen OB, Chitty LS. Fetal genital anomalies: an aid to
diagnosis. Prenat Diagn 2008;28:389-398.
203. Mazza V, Di Monte I, Ceccarelli PL, et al. Prenatal diagnosis of
female pseudohermaphroditism associated with bilateral luteoma of
pregnancy: case report. Hum Reprod 2002;17:821-824.
204. Picone O, Laperelle J, Sonigo P, et al. Fetal magnetic resonance
imaging in the antenatal diagnosis and management of hydrocolpos.
Ultrasound Obstet Gynecol 2007;30:105-109.
205. Hayashi S, Sago H, Kashima K, et al. Prenatal diagnosis of
fetal hydrometrocolpos secondary to a cloacal anomaly by magnetic
resonance imaging. Ultrasound Obstet Gynecol 2005;26:577-
579.
206. Dhombres F, Jouannic JM, Brodaty G, et al. Contribution of prenatal imaging to the anatomical assessment of fetal hydrocolpos.
Ultrasound Obstet Gynecol 2007;30:101-104.
207. Garel L, Filiatrault D, Brandt M, et al. Antenatal diagnosis of ovarian
cysts: natural history and therapeutic implications. Pediatr Radiol
1991;21:182-184.
208. Nussbaum AR, Sanders RC, Hartman DS, et al. Neonatal ovarian
cysts: sonographic-pathologic correlation. Radiology 1988;168:
817-821.
1388 PART IV ■ Obstetric Sonography
209. Heling KS, Chaoui R, Kirchmair F, et al. Fetal ovarian cysts: prenatal
diagnosis, management and postnatal outcome. Ultrasound Obstet
Gynecol 2002;20:47-50.
210. Meizner I, Levy A, Katz M, et al. Fetal ovarian cysts: prenatal ultrasonographic detection and postnatal evaluation and treatment. Am
J Obstetr Gynecol 1991;164:874-878.
211. Giorlandino C. Antenatal ultrasonographic diagnosis and management of fetal ovarian cysts. Int J Gynecol Obstet 1994;44:27-31.
212. Bagolan P, Giorlandino C, Nahom A, et al. The management of fetal
ovarian cysts. J Pediatr Surg 2002;37:25-30.
213. Bryant AE, Laufer MR. Fetal ovarian cysts: incidence, diagnosis and
management. J Reprod Med 2004;49:329-337.
214. Monnery-Noche ME, Auber F, Jouannic JM, et al. Fetal and
neonatal ovarian cysts: is surgery indicated? Prenat Diagn 2008;
28:15-20.
CHAPTER 40
The Fetal
Musculoskeletal System
Phyllis Glanc, David Chitayat, and Sheila Unger
Chapter Outline
NORMAL FETAL SKELETON
Development
Extremity Measurements
SONOGRAPHIC EVALUATION OF
FETUS WITH SKELETAL
DYSPLASIA
Positive Family History
Abnormal Bone Length or
Appearance
Three-Dimensional Ultrasound
Additional Imaging
LETHAL SKELETAL DYSPLASIAS
Thanatophoric Dysplasia
Achondrogenesis
Osteogenesis Imperfecta
Hypophosphatasia
Campomelic Dysplasia
Short-Rib Polydactyly Syndromes
Other Dysplasias
NONLETHAL OR VARIABLE-
PROGNOSIS SKELETAL
DYSPLASIAS
Heterozygous Achondroplasia
Diastrophic Dysplasia
Asphyxiating Thoracic Dysplasia
Ellis–van Creveld Syndrome
Chondrodysplasia Punctata
Dyssegmental Dysplasia
Osteogenesis Imperfecta Types I, III,
IV—Nonlethal Types
Congenital bone disorders are a heterogeneous group
of disorders primarily affecting the growth and development of the musculoskeletal system. There are three
major categories. The skeletal dysplasias are developmental disorders of chondro-osseous tissue caused by singlegene disorders with prenatal and postnatal manifestations.
the dysostoses are single-gene disorders resulting in malformations of individual bones caused by transient
abnormalities of signaling factors. Disruptions are morphologic defects of an organ or larger region resulting
from extrinsic breakdown or interference with an originally normal developmental process.
skeletal dysplasias, also called osteochondrodysplasias,
diagnosed prenatally or during the neonatal period,
excluding limb amputations, is 2.4 to 4.5 per 10,000
births. More than 400 subtypes have been reported
(Table 40-1).
The number of recognized genetic disorders with a
substantial skeletal component is increasing, and the distinction among dysplasias, metabolic bone disorders,
dysostoses, and malformation syndromes is constantly
evolving. Despite increased knowledge about the genetic
etiology of many of these conditions and the improved
ability to diagnose and categorize these disorders correctly, the clinical and imaging features remain a fundamental tool for diagnosing and directing the molecular
1
The prevalence of
2-5
LIMB REDUCTION DEFECTS AND
ASSOCIATED CONDITIONS
Proximal Focal Femoral Deficiency
Caudal Regression Syndrome and
Sirenomelia
Amniotic Band Sequence
Limb Reduction Defects
Radial Ray Defects
Arthrogryposis Multiplex Congenita
HAND AND FOOT DEFORMITIES
SKELETAL FINDINGS
ASSOCIATED WITH
ANEUPLOIDY
2,6
investigation.
Although many fetal skeletal dysplasias
can be accurately identified by prenatal ultrasound, this
remains a challenging task because of the low incidence,
phenotypic variability and wide range of appearances.
The majority of cases have no family history of a similar
condition. Nonetheless, the majority of lethal skeletal
dysplasias, including thanatophoric dysplasia, achondrogenesis, and osteogenesis imperfecta type II, can be
diagnosed solely on the basis of prenatal ultrasound.
Tretter et al.9 determined that 26 of 27 lethal skeletal
dysplasias were identified correctly by prenatal ultrasound; however, only 13 of 27 (48%) received an accurate specific antenatal diagnosis.
9
Eight of 14 (57%)
underwent a substantial change in genetic counseling
when cytogenetic, molecular (including microarray),
pathologic, and radiologic findings were added. Thus,
although the ultrasound diagnosis of a lethal skeletal
dysplasia is highly accurate (85%-95%), a correct specific diagnosis is obtained in only 40% to 55% of
7-9
cases.
Nonetheless, the highly accurate prenatal determination of the lethality of a given skeletal dysplasia is crucial
in helping couples with decision making. Typically, a
combination of ultrasound, radiologic, genetic, pathologic, and cytogenetic investigation is required to classify
a specific congenital musculoskeletal disorder. A prenatal
7
8
1389
1390 PART IV ■ Obstetric Sonography
TABLE 40-1. BIRTH PREVALENCE OF
SKELETAL DYSPLASIAS
SKELETAL DYSPLASIA
Lethal Dysplasias
Thanatophoric dysplasia 2.4 to 6.9
Achondrogenesis 0.9 to 2.3
Osteogenesis imperfecta type IIA 1.8
Hypophosphatasia congenita 1.0
Variable-Prognosis Dysplasias
Rhizomelic chondrodysplasia punctata 0.5 to 0.9
Campomelic dysplasia 1.0 to 1.5
Asphyxiating thoracic dystrophy 0.8 to 1.4
Ellis–van Creveld syndrome 0.7
Osteogenesis imperfecta (other types) 1.8
Nonlethal Dysplasias
Heterozygous achondroplasia 3.3 to 3.8
Overall 24.4 to 75.0
PREVALENCE PER
100,000 BIRTHS
diagnosis of a musculoskeletal anomaly will provide an
opportunity for genetic counseling, pregnancy termination, or tertiary-level care when appropriate. A multidisciplinary approach involving the medical imaging team,
obstetrician, medical geneticist, and perinatologist is
important in optimizing the accuracy of prognosis and
recurrence risk. This information is crucial to the family
and to medical personnel involved in planning clinical
management for both current and future pregnancies.
This chapter uses a “key features’’ approach to the sonographic diagnosis of the common skeletal dysplasias to
aid in the classification and differential diagnosis.
Of the secondary ossification centers in the long
bones, only the distal femoral epiphysis, the proximal
tibial epiphysis, and occasionally the proximal humeral
epiphysis ossify prenatally (Fig. 40-1). The unossified
epiphysis appears hypoechoic, with a variably, mildly
echogenic center. Ossification begins centrally. The
distal femoral epiphysis can ossify as early as 29 weeks’
menstrual age and as late as 34 weeks. When it measures
greater than 7 mm, the menstrual age is generally later
than 37 weeks.
to ossify by 35 menstrual weeks.
14,15
The proximal tibial epiphysis begins
15
In uncomplicated
pregnancies the combination of a distal femoral epiphysis of 3 mm or greater and the presence of a proximal
tibial epiphysis is considered a reliable marker of pulmonary maturity.16 Intrauterine growth restriction
(IUGR) may delay ossification of the distal femoral
epiphysis and proximal tibial epiphysis. The earliest secondary epiphysis to ossify is the calcaneus, at approximately 20 weeks’ gestation, thus marking the earliest
point that assessment of delayed ossification of the secondary epiphyseal centers can be attempted.
The fascia within the muscle is highly echogenic
compared with the relatively hypoechoic cartilage. The
fetal musculature is slightly more echogenic than the
relatively hypoechoic cartilage. The fetal joint spaces, in
particular the knee, appear echogenic because of the
combination of synovium, fat, and microvasculature.
11
The normal development and ultimate function of the
fetal musculoskeletal system depend on fetal move-
ments, which start by the second half of the first trimester. In the absence of normal fetal motion, the bones and
muscles will be underdeveloped, the chest will be narrow,
and joint contractures and postural deformities may
also occur.
NORMAL FETAL SKELETON
Development
The high level of intrinsic contrast of the fetal extremities
places them among the earliest structures that can be
evaluated by ultrasound. By the end of the embryonic
period, the differentiation of bones, joints, and musculature is similar to that of an adult and is associated with
increased fetal movements.
can demonstrate the limb buds by 7 weeks’ gestation,
and the foot and hand plates are visible by 8 weeks.
Osteogenesis begins in the clavicle and mandible by 8
weeks as well. By 11 to 12 weeks, the primary ossifica-
tion centers of the long bones (e.g., scapula, ileum),
as well as the limb articulations and phalanges, can
be identified. The ischium, metacarpals, and metatarsals
ossify during the fourth month of gestation. The pubis,
calcaneus, and talus ossify during the fifth and sixth
months. Ossification of the other tarsal and carpal bones
occurs postnatally.
13
The direction of growth in the long
bones is from proximal to distal, and the lower extremities lag slightly behind the upper extremities.
10,11
Transvaginal ultrasound
11
12
Extremity Measurements
It is a standard practice to assess femur length (FL) as
part of the evaluation of fetal size and morphology.
Although measurement of all the long bones is not
required in a routine obstetric ultrasound, an overall
evaluation of the fetal skeleton should be performed to
ensure the presence and bilateral symmetry of the tubular
bones. Available charts provide guidance for correlating
the length of the extremities with the gestational age
(Table 40-2).
The longest femur measurement, excluding both
proximal and distal epiphyses, is usually chosen. The
inclusion of the distal femur point, or the specular
reflection of the lateral aspect of the distal femoral
epiphysis cartilage, is the most common reason for
overestimating FL
17
(Fig. 40-2, A). An oblique FL
measurement will result in undermeasurement. The
lateral border of the femur in the near field of the transducer appears straight, whereas the medial border of
the femur in the far field has a curved appearance
(Fig. 40-2, B).
18
A B
FIGURE 40-1. Secondary ossification centers in fetus at 38 weeks’ gestational age. A, View of the femur and
distal femoral ossification center (arrow). B, View of distal femur and proximal tibia with distal femoral ossification center (arrow) and
proximal tibial ossification center (arrowhead).
TABLE 40-2. NORMAL EXTREMITY LONG-BONE LENGTHS AND BIPARIETAL DIAMETERS
AT DIFFERENT MENSTRUAL AGES*
MENSTRUAL
AGE
13 2.3 (0.3) 1.1 (0.2) 0.9 (0.2) 0.8 (0.2) 1.0 (0.2) 0.6 (0.2) 0.8 (0.3)
14 2.7 (0.3) 1.3 (0.2) 1.0 (0.2) 0.9 (0.3) 1.2 (0.2) 0.8 (0.2) 1.0 (0.2)
15 3.0 (0.1) 1.5 (0.2) 1.3 (0.2) 1.2 (0.2) 1.4 (0.2) 1.1 (0.1) 1.2 (0.1)
16 3.3 (0.2) 1.9 (0.3) 1.6 (0.3) 1.5 (0.3) 1.7 (0.2) 1.4 (0.3) 1.6 (0.3)
17 3.7 (0.3) 2.2 (0.3) 1.8 (0.3) 1.7 (0.2) 2.0 (0.4) 1.5 (0.3) 1.7 (0.3)
18 4.2 (0.5) 2.5 (0.3) 2.2 (0.3) 2.1 (0.3) 2.3 (0.3) 1.9 (0.2) 2.2 (0.3)
19 4.4 (0.4) 2.8 (0.3) 2.5 (0.3) 2.3 (0.3) 2.6 (0.3) 2.1 (0.3) 2.4 (0.3)
20 4.7 (0.4) 3.1 (0.3) 2.7 (0.2) 2.6 (0.2) 2.9 (0.3) 2.4 (0.2) 2.7 (0.4)
21 5.0 (0.5) 3.5 (0.4) 3.0 (0.4) 2.9 (0.4) 3.2 (0.4) 2.7 (0.4) 3.0 (0.4)
22 5.5 (0.5) 3.6 (0.3) 3.2 (0.3) 3.1 (0.3) 3.3 (0.3) 2.8 (0.5) 3.1 (0.4)
23 5.8 (0.5) 4.0 (0.4) 3.6 (0.2) 3.4 (0.2) 3.7 (0.3) 3.1 (0.4) 3.5 (0.2)
24 6.1 (0.5) 4.2 (0.3) 3.7 (0.3) 3.6 (0.3) 3.8 (0.4) 3.3 (0.4) 3.6 (0.4)
25 6.4 (0.5) 4.6 (0.3) 4.0 (0.3) 3.9 (0.4) 4.2 (0.4) 3.5 (0.3) 3.9 (0.4)
26 6.8 (0.5) 4.8 (0.4) 4.2 (0.3) 4.0 (0.3) 4.3 (0.3) 3.6 (0.4) 4.0 (0.3)
27 7.0 (0.3) 4.9 (0.3) 4.4 (0.3) 4.2 (0.3) 4.5 (0.2) 3.7 (0.3) 4.1 (0.2)
28 7.3 (0.5) 5.3 (0.5) 4.5 (0.4) 4.4 (0.3) 4.7 (0.4) 3.9 (0.4) 4.4 (0.5)
29 7.6 (0.5) 5.3 (0.5) 4.6 (0.3) 4.5 (0.3)
30 7.7 (0.6) 5.6 (0.3) 4.8 (0.5) 4.7 (0.3) 5.0 (0.5) 4.1 (0.6) 4.7 (0.3)
31 8.2 (0.7) 6.0 (0.6) 5.1 (0.3) 4.9 (0.5) 5.3 (0.4) 4.2 (0.3) 4.9 (0.4)
32 8.5 (0.6) 6.1 (0.6) 5.2 (0.4) 5.1 (0.4) 5.4 (0.4) 4.4 (0.6) 5.0 (0.6)
33 8.6 (0.4) 6.4 (0.5) 5.4 (0.5) 5.3 (0.3) 5.6 (0.5) 4.5 (0.5) 5.2 (0.3)
34 8.9 (0.5) 6.6 (0.6) 5.7 (0.5) 5.5 (0.4) 5.8 (0.5) 4.7 (0.5) 5.4 (0.5)
35 8.9 (0.7) 6.7 (0.6) 5.8 (0.4) 5.6 (0.4) 5.9 (0.6) 4.8 (0.6) 5.4 (0.4)
36 9.1 (0.7) 7.0 (0.7) 6.0 (0.6) 5.6 (0.5) 6.0 (0.6) 4.9 (0.5) 5.5 (0.3)
37 9.3 (0.9) 7.2 (0.4) 6.1 (0.4) 6.0 (0.4) 6.1 (0.4) 5.1 (0.3) 5.6 (0.4)
38 9.5 (0.6) 7.4 (0.6) 6.2 (0.3) 6.0 (0.4) 6.4 (0.3) 5.1 (0.5) 5.8 (0.6)
39 9.5 (0.6) 7.6 (0.8) 6.4 (0.7) 6.1 (0.6) 6.5 (0.6) 5.3 (0.5) 6.0 (0.6)
40 9.9 (0.8) 7.7 (0.4) 6.5 (0.3) 6.2 (0.1) 6.6 (0.4) 5.3 (0.3) 6.0 (0.5)
41 9.7 (0.6) 7.7 (0.4) 6.6 (0.4) 6.3 (0.5) 6.6 (0.4) 5.6 (0.4) 6.3 (0.5)
42 10.0 (0.5) 7.8 (0.7) 6.8 (0.5) 6.7 (0.7) 6.8 (0.7) 5.7 (0.5) 6.5 (0.5)
BIPARIETAL
DIAMETER
FEMUR TIBIA FIBULA HUMERUS RADIUS ULNA
Bone
4.8 (0.4) 4.0 (0.5) 4.5 (0.4)
From Merz E, Kim-Kern MS, Pehl S: Ultrasonic mensuration of fetal limb bones in the second and third trimesters. J Clin Ultrasound 1987;5:175-183.
*Mean values (cm); value of 2 SD in parentheses.
1392 PART IV ■ Obstetric Sonography
A B C
D
E
G H
FIGURE 40-2. Normal femur and spectrum of abnormal appearances. A, Normal femur: measure the longest length,
excluding the proximal and distal epiphysis and the specular reflection of the lateral aspect of the distal femoral epiphysis (arrow).
B, Normal femur in the near field, with straight lateral border versus the curved medial border in the far field of the transducer. C, Isolated
hypoplastic left femur (arrowhead), with normal tibia (black arrow) and foot (white arrow). D, Osteogenesis imperfecta type I. Isolated
femoral fracture with acute angulation (arrow). E, Campomelic dysplasia. Mild shortening and a gently curved ventral femoral bowing
(arrow). F, Osteogenesis imperfecta type IIA. Bowed femur with multiple discontinuities representing fractures. G, Hypophosphatasia
congenita. Severe micromelia (relatively broad metaphysis, short diaphysis). H, Thanatophoric dysplasia. Curved, “telephone receiver’’
femur. I, Chondrodysplasia punctata. Third-trimester appearance of a stippled epiphysis. (C courtesy Ants Toi, MD; D and E courtesy Shia
Salem, MD; University of Toronto.)
In the lower extremity the lateral bone is the fibula
and the medial bone is the tibia. The tibia and fibula
end at the same level distally. In the upper extremity,
pronation may cause the radius and ulna to cross, so it
can be difficult to distinguish the ulna from the radius
using lateral and medial positions. The ulna is distinguished from the radius by its longer proximal extent
and its relationship to the fifth digit distally. The radius
and ulna end at the same level distally. Demonstration
of this relationship will effectively exclude the majority
of radial ray defects.
The clavicles grow in a linear fashion, approximately
1 mm per week, and the gestational age in weeks is
approximately the length of the clavicle in millimeters
from 14 weeks to term. By 40 weeks’ gestation, the
clavicles measure approximately 40 mm.
F
I
19
Chapter 40 ■ The Fetal Musculoskeletal System 1393
A B
FIGURE 40-3. Foot length measurement. From the skin edge overlying the calcaneus to the distal end of the longest toe. A,
Sagittal measurement; note the normal squared appearance of the heel. B, Plantar measurement.
Foot length is measured from the skin edge overlying
the calcaneus to the distal end of the longest toe (the
first or second toe) on either the plantar or the sagittal
20-22
view
(Fig. 40-3). The ossified femur length is almost
equivalent to the foot length, resulting in a normal
femur/foot length ratio of approximately 1.0. This
ratio remains relatively constant from the 14th week of
gestation onward. If the fetus is constitutionally small or
there is symmetrical IUGR, the ratio is generally 0.9 or
greater. In most skeletal dysplasias characterized by
short limbs, the ratio is generally less than 0.9 because
of the relative sparing of the hands and feet. The greater
the deviation from the lower limits of the norm, the
greater is the severity.
SONOGRAPHIC EVALUATION
OF FETUS WITH SKELETAL
DYSPLASIA
A prenatal evaluation of a skeletal dysplasia is indicated
if there is a positive family history or an abnormal length
or appearance of the bones at ultrasound.
ASSESSMENT OF SKELETAL
DYSPLASIAS: KEY FEATURES
Family history
Serial measurements
Degree of limb shortening
Pattern of limb shortening
Presence of bowing, fractures, and angulations
Spine
Thoracic measurements
Hands and feet
Calvarium and facial features
Positive Family History
A positive family history of a sibling or parents affected
by a skeletal dysplasia or consanguineous parents should
prompt an intensive ultrasound investigation with a
focus on targeted abnormalities and serial measurements.
A history of consanguinity is important because many of
the skeletal dysplasias have an autosomal recessive mode
of inheritance. Heterozygous achondroplasia, the most
common nonlethal skeletal dysplasia, has an autosomal
dominant pattern of inheritance. Family history may not
be helpful because 80% of cases are caused by a new
dominant mutation.
Abnormal Bone Length
or Appearance
The fetal femur is often the only long bone routinely
measured at the second-trimester ultrasound evaluation.
An abnormal FL is traditionally defined as below −2
standard deviations (SD) for gestational age.
23,24
Using
this cutoff, 2.5% of all fetuses would be classified
as having short limbs. This exceeds the expected frequency of skeletal dysplasias, and thus additional investigations are needed to identify the fetus with a skeletal
dysplasia.
When one or all of the long bones measure less than
2 SD for gestational age, a follow-up ultrasound should
−
be done in 3 to 4 weeks to evaluate the interval growth.
If the interval femur growth is normal, there is a high
likelihood that the fetus does not have skeletal dysplasia.
However, further deviation from the mean by at least
1 SD should suggest the presence of a skeletal dysplasia
or severe IUGR. When FL measures below −4 SD for
gestational age, there is a high likelihood of a skeletal
dysplasia. Kurtz et al.23 have shown that the number of
millimeters below the −
2 SD line is a simple screening
1394 PART IV ■ Obstetric Sonography
tool to evaluate femoral shortening with the following
guidelines:
• If FL is 1 to 4 mm below the −2 SD point, further
serial measurements are required to determine if a
skeletal dysplasia is present.
• If FL is greater than 5 mm below the −2 SD point,
there is a high likelihood of a skeletal dysplasia.
The most common etiology of a so-called short femur
is either inaccurate dating or a normal variant in a constitutionally small fetus, which may be associated with a
parental or family history of less-than-average stature. In
about 13% of cases, a remeasurement will bring the FL
into a normal range, likely representing a false-positive
diagnosis rather than a growth-spurt.
25
Isolated, symmetrical short femurs identified at the second midtrimester ultrasound evaluation are helpful in identifying a
group of fetuses at increased risk for low birth weight,
small for gestational age, or severe IUGR.
25-27
Typically,
these fetuses will also have small abdominal circumference measurements.
Occasionally, severe IUGR may present with greatly
shortened long bones.
28
Associated findings of normal
or decreased skin fold measurements, oligohydramnios,
abnormal placental morphology, and abnormal Doppler
waveforms suggest the diagnosis of IUGR,
29
whereas
redundant, thickened skin folds and polyhydramnios
typically accompany short-limb dysplasias.
Nonlethal skeletal dysplasias such as heterozygous
achondroplasia are generally not evident before 20
weeks’ gestation. The findings of short long bones before
20 weeks indicate a more serious and usually fatal skeletal dysplasia. As a rule, the earlier the detection of limb
shortening, the worse is the prognosis. Virtually all cases
diagnosed in first trimester are considered severe skeletal
dysplasias, with the greater majority representing lethal
conditions.
available.
30
First-trimester skeletal biometry tables are
31
Although mild, isolated shortening of the
femur indicates increased risk for trisomy 21 by 1.5fold, other factors are more important for assessing
this risk.
32
The pattern of limb shortening should be assessed
to determine which long-bone segments are most severely
affected
8,33
(Fig. 40-4). Rather than millimeters, we find
it useful to standardize measurements to “weeks of size”
to determine disproportion. There are four main patterns of shortening of the long bones: rhizomelia, shortening of the proximal segment (femur and humerus);
mesomelia, shortening of the middle segment (radius,
ulna, tibia, and fibula); acromelia, shortening of
the distal segment (hands and feet); and micromelia,
shortening of the entire limb (mild, mild/bowed, or
severe).
PATTERNS OF LIMB SHORTENING
Rhizomelia: shortening of proximal segment
(femur, humerus).
Mesomelia: shortening of middle segment (radius,
ulna/tibia, fibula).
Acromelia: shortening of distal segment (hands,
feet).
Micromelia: shortening of entire limb (mild, mild/
bowed, severe).
FIGURE 40-4. Patterns of limb shortening. Left to right, Normal, mesomelia, rhizomelia, mild micromelia, mild and curved
micromelia, and severe micromelia. (Drawing courtesy J. Tomash, MD, University of Toronto.)
A B
Chapter 40 ■ The Fetal Musculoskeletal System 1395
FIGURE 40-5. In lethal skeletal dysplasias, assessment of the fetal spine
ossification centers can provide helpful clues to the specific diagnosis. The
following cases are all lethal on the basis of pulmonary hypoplasia, as
evidenced by short ribs and a small thoracic circumference. A, Short-rib
polydactyly syndrome with normal ossification of all three spine ossification centers (circle). B, Achondrogenesis with demineralization of all three
spine ossification centers (circle). C, Hypophosphatasia with demineraliza-
C
tion of the posterior ossification centers but mineralization of the vertebral
body (circle).
The shape, contour, and density of the bones should
be assessed for the presence of bowing, angulations, fractures, or thickening. Bowing is a nonspecific finding,
typically caused by underlying osseous fragility. Although
more than 40 distinct disorders can be associated
with bowed, bent, or angulated femurs, the majority
(63%) belong to three disorders: campomelic dysplasia
(24.4%), thanatophoric dysplasia (23.9%) and osteo-
genesis imperfecta (OI) (18.1%).
34
Patients with OI
types I and IV can present with apparent in utero bowing
and shortening without frank fractures of the long bones
(see Fig. 40-2, D). Anterior bowing of the tibia, femur,
and humerus may suggest the diagnosis of campomelic
dysplasia; associated findings such as hypoplastic scapu-
lae and cervical kyphosis are typically present. Bone
fractures may appear as angulations or interruptions in
the bone contour or as thick, wrinkled contours corresponding to repetitive cycles of fracture and callus formation (Fig. 40-2, F). Decreased or absent acoustic
shadowing is a marker for decreased mineralization of
the long bones. When evident, this is helpful, but in its
absence the bone mineralization may still be abnormal.
The spine is assessed for segmentation anomalies,
kyphoscoliosis, platyspondyly (flattened vertebral
bodies), demineralization, myelodysplasia, and caudal
regression syndromes. Although platyspondyly is the
most common spine abnormality, it is a challenging prenatal diagnosis.
35
Demineralization of the spine can result
in the appearance of ghost vertebrae or nonvisualization
of one or all of the three ossification centers (Fig. 40-5).
A progressively narrowed lumbar interpedicular distance
is associated with achondroplasia; a widened interpedicular distance is associated with myelodysplasia.
The most important prognostic determinant of the
lethality of a given skeletal dysplasia is the presence of
pulmonary hypoplasia. Ultrasound is 85% to 95%
accurate in the diagnosis of a lethal skeletal dysplasia on
the basis of pulmonary hypoplasia.
7,8
The thoracic cir-
cumference is measured at the level of the four-chamber
heart and compared to nomograms (see Table 36-1). A
thoracic/abdominal circumference ratio of less than 0.8
is considered abnormal. The thoracic length (from the
neck to the diaphragm) is also measured, and the ribs are
assessed to determine if they are short. At the level of the
1396 PART IV ■ Obstetric Sonography
A B C
FIGURE 40-6. Triplet B affected with campomelic dysplasia and pulmonary hypoplasia. Coronal ultrasound
images of the thorax in triplet pregnancy at 27 weeks’ gestation. A, Normal triplet A shows normal convex contour of the thorax. Calipers
measure the scapula. B, Triplet B shows a bell-shaped thorax. C, Radiograph of triplet B confirms a bell-shaped thorax consistent with
pulmonary hypoplasia.
four-chamber cardiac view, the ribs should normally
encircle at least 70% to 80% of the thoracic circumfer-
36
The ribs remain in a relatively horizontal plane, as
ence.
does the cardiac axis, facilitating this evaluation. In a sagittal view, a markedly narrowed anteroposterior (AP) diameter of the thorax is associated with pulmonary hypoplasia.
In the coronal view, a concave or bell-shaped contour is
1
associated with pulmonary hypoplasia (Fig. 40-6).
The hands and feet are examined for deformities such
as clubfoot or clubhand. A hitchhiker thumb, or
abducted thumb, is associated with diastrophic dwarf-
ism. Fixed postural deformities may suggest the diagnosis of arthrogryposis multiplex congenita. Polydactyly
is associated with short-rib polydactyly syndromes,
Ellis–van Creveld syndrome, asphyxiating thoracic
dystrophy and some chromosomal abnormalities.
The fetal cranium is assessed for the presence of
macrocranium, frontal bossing, cloverleaf skull
deformity, underlying brain abnormalities, and facial
abnormalities, such as saddle nose, hypertelorism, and
cleft lip and palate. An abnormal cranial contour may
12
indicate craniosynostosis or premature fusion of the
sutures. The most reliable sonographic sign of demineralization is increased compressibility of the calvarium.
This finding is typically present in osteogenesis imper-
fecta type II, achondrogenesis, and hypophosphata-
FIGURE 40-7. Normal ribs: 3-D ultrasound.
sia. The falx may appear abnormally bright or echogenic
compared to the demineralized calvarium.
The ribs are assessed to ensure an adequate length,
thus minimizing the risk of pulmonary hypoplasia, and
are examined for abnormal number or appearance.
37
The
finding of an abnormal number of fetal ribs is an isolated
finding of no clinical importance in the majority of
37
associated with minor anomalies in a smaller
cases,
group (29%) and only occasionally associated with severe
malformations. Associated syndromes include Poland
syndrome, VACTERL association (vertebral abnormalities, anal atresia, cardiac abnormalities, tracheoesopha-
geal fistula, renal agenesis and dysplasia, limb defects),
cleidocranial dysplasia, campomelic dysplasia, and
chromosome abnormalities. Three-dimensional ultrasound volume images aid in accurately counting the
number of ribs (Fig. 40-7).
Ultimately, a detailed examination of each bone may
be required to determine the fetal condition. Specific
dysmorphic features of bones (e.g., clavicular or scapular
hypoplasia; aplasia of fibula, tibia, or radius; platyspondyly) can be helpful to further define a specific skeletal
dysplasia. A detailed evaluation of the cardiovascular,
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