Case Study: Fetal Pulmonary Anomaly

March 27, 2014

A routine ultrasound exam reveals unexpected findings in the lungs of a 29-week fetus. What’s your diagnosis?

A 30-year-old patient, gravida 2 para 1, presented at 29 weeks’ gestation for routine ultrasound screening. Her menstrual cycles prior to this pregnancy have been normal. She had no history of diabetes mellitus, hypertension, or any other major illness.

Present pregnancy: The patient has been amenorrheic for 29 weeks, which almost corresponds with the age of the fetus on ultrasound scan. She had mild hemorrhagic discharge during the first month of this pregnancy but since has reported no other issues.

Clinical examination: Blood pressure was normal at 128/75 mm Hg. Other vital signs were within normal limits as well. No abnormalities were noted on chest examination. On abdominal examination, the fundal height matched the gestational age of 29 weeks.

Imaging studies: This patient underwent routine transabdominal ultrasound screening to exclude any congenital fetal anomalies. She had not undergone any previous ultrasound examination during this pregnancy. The B-mode ultrasound images showing sagittal sections of the fetal chest and abdomen follow.

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What are your findings based on these two images?
Ultrasound Findings

Figure 1, a sagittal section of the fetal chest and abdomen, shows a placenta that appears to be anterior and grossly normal. There is also evidence of normal levels of amniotic fluid in the uterine cavity. One notable finding is a brightly echogenic area in the fetal thorax. Where is this lesion located?

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Figure 2 shows an echogenic lesion that appears to be within the thoracic cage and in the left hemithorax. On careful observation, we find that in addition to the echogenic area in the left hemithorax, the heart has been shifted across the midline to the opposite side. What are the implications of this finding, or rather all the findings put together? Does the abnormality lie in the left hemithorax, or is it in the right hemithorax?

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It needs to be deciphered whether the right lung is pulling the heart to the right side, or whether the fetal heart is being pushed to the right side by the lesion in the left hemithorax. Is the echogenicity of the right lung normal? If we compare the echogenicity of a normal fetal lung to the lungs of this fetus, we realize that the right lung is normal. The extremely high echogenicity of the left hemithorax suggests that this is abnormal. Figure 3 and Figure 4 may offer a clearer picture of what is happening to the left lung.

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Diagnostic Considerations

Among the possible differential diagnoses is a diaphragmatic hernia or consolidation of the fetal lung. The displacement of the abdominal structures and organs into the left hemithorax could suggest a diaphragmatic hernia, but the stomach bubble is located just below the left dome of diaphragm, which is normal. Therefore, congenital diaphragmatic hernia can be excluded.

Another possibility is consolidation of the fetal lung. In an adult patient, this diagnosis would be likely. However, this is an unlikely finding in a fetus.

In review of the findings, there is evidence of:

- A large, echogenic lesion in the left hemithorax.

- Significant midline shift and displacement of the heart to the right side.

- Normally located stomach, well within the confines of the abdominal cavity.

The lung conditions that can cause brightly echogenic mass lesions of the lungs in a fetus are pulmonary sequestration and congenital cystic adenomatoid malformation (CCAM). Both diagnoses are relatively rare. CCAM is characterized by multiple small or large cystic lesions within a segment of lung tissue along with abnormal bronchial proliferation. This gives rise to a mass of cystic segmental lung tissue, which may show features similar to this case. However, there is no evidence of any cystic lesions in these images, leaving the possibility of pulmonary sequestration.

Pulmonary sequestration is characterized by a small or large segment of abnormal lung tissue that has no connection with the bronchial tree, thus giving rise to an echogenic small or large mass, usually located just below the left lung and above the diaphragm. Such mass lesions can produce significant mediastinal shift, which is seen in this case.

Final Diagnosis

Fetal extralobar pulmonary sequestration

Discussion

Fetal pulmonary sequestration is characterized by the development of sequestrated lung tissue that is separate from the rest of the tracheobronchial tree. Medical literature describes two varieties of pulmonary sequestration: intralobar and extralobar.

Intralobar sequestration usually develops during adulthood and is characterized by aberrant lung tissue of sequestrated lung included within the pleural covering of the lung itself. Extralobar sequestration occurs when the aberrant lung tissue has a separate pleural covering of its own. Almost all cases of pulmonary sequestration seen during the intrauterine period are extralobar in nature.

Differential Diagnoses

The main differential diagnoses for pulmonary sequestration include CCAM, congenital diaphragmatic hernia, bronchogenic cyst, and neuroblastoma. As previously mentioned, the characteristic findings seen in this anomaly can clearly differentiate pulmonary sequestration from all other possible diagnoses.

Disclosures:

All images from this case are courtesy of Sunil Yadav, MD.

References:

Dhingsa R, Coakley FV, Albanese CT, et al. Prenatal sonography and MR imaging of pulmonary sequestration. AJR Am J Roentgenol. 2003;180:433-437. Available here.

Rumack CM, Wilson SR, Charboneau JW, Levine D, eds. Diagnostic Ultrasound. 4th ed. Philadelphia: Mosby; 2011.