Pulmonary hypoplasia (PH) refers to deficient or incomplete development of parts of the lung. It can develop as a result of a number of other in-utero anomalies.
The true prevalence is not well known (1.4% of all births according to Knox et.al 13), but in cases of premature rupture of membranes at 15-28 weeks gestation, the reported prevalence of pulmonary hypoplasia ranges from 9 to 28% 2.
It is characterised by the presence of both bronchi (albeit rudimentary) and alveoli in an under-developed lobe. Both the size and the weight of the lung is reduced.
There are normally four stages of fetal lung development where the pathological process can occur at any level
- embryonic: from conception ~5th week
- pseudoglandular: from ~5th -17th week
- canalicular: from ~16th - 24th week: this stage may be more affected by oligohydramnios
- terminal sac or alveolar period: from 24th week to term and beyond
There are several key factors required for the adequate development of the lung. These are:
- sufficient amniotic fluid volumes
- adequate thoracic space-size
- normal breathing movement
- normal fluid within the lung
A deficiency in any of these could lead to pulmonary hypoplasia.
Most cases of pulmonary hypoplasia are secondary to other congenital anomalies or pregnancy complications. Some cases however can occur as a primary event 5.
With secondary causes, it can result from factors directly or indirectly compromising the thoracic space available for lung growth.
Intra-thoracic causes include:
- congenital diaphragmatic hernia: most common intrathoracic cause
- extralobar sequestration
- agenesis of the diaphragm
- mediastianal mass(es)/tumour(s):
- decreased pulmonary vascular (arterial) perfusion:
Extra-thoracic causes include:
- oligohydramnios: and its causes
- skeletal dysplasias: especially those causing a narrow fetal thorax
- large intra-abdominal mass compressing the thorax
- neuromuscular conditions interfering with fetal breathing
Other associations include:
Ultrasound may show ancillary features such as the presence of oligohydramnios and/or also show any of the causative anomalies.
Several sonographic parameters may give indirectly clues as to the presence and extent of pulmonary hypoplasia. Such include:
- fetal lung head ratio: reduced (ratios less than 1 usually indicate a poor prognosis)
- fetal chest circumference (or thoracic circumference-TC) 6: reduced
(In the case of intra-thoracic causes, both these parameters can be normal)
Femur length to abdominal circumference < 0.16 15.
Peripheral pulmonary arterial resistance is often increased with pulmonary hypoplasia
May be be useful to more accurate calculate lung volumes.
- T1: normal fetal lung is usually low signal on T1; more to be added
- T2: normal fetal long is usually high signal on T2; more to be added
- HASTE: fetuses with pulmonary hypoplasia are thought to have low signal 1
Treatment and prognosis
The presence or development of pulmonary hypoplasia is often a critical determining feature in fetal survival in context of other potential causative anomalies. Treatment will significantly depend on the presence of underlying / associated anomalies.
In adult cases of unilateral pulmonary hypoplasia, consider conditions associated with a small hemi-thorax such as:
- 1. Kuwashima S, Nishimura G, Iimura F et-al. Low-intensity fetal lungs on MRI may suggest the diagnosis of pulmonary hypoplasia. Pediatr Radiol. 2001;31 (9): 669-72. doi:10.1007/s0024710310669 - Pubmed citation
- 2. Berrocal T, Madrid C, Novo S et-al. Congenital anomalies of the tracheobronchial tree, lung, and mediastinum: embryology, radiology, and pathology. Radiographics. 24 (1): e17. doi:10.1148/rg.e17 - Pubmed citation
- 3. Lauria MR, Gonik B, Romero R. Pulmonary hypoplasia: pathogenesis, diagnosis, and antenatal prediction. Obstet Gynecol. 1995;86 (3): 466-75. doi:10.1016/0029-7844(95)00195-W - Pubmed citation
- 4. Mutlu H, Basekim C, Silit E et-al. Gadolinium-enhanced 3D MR angiography of pulmonary hypoplasia and aplasia. AJR Am J Roentgenol. 2006;187 (2): 398-403. doi:10.2214/AJR.04.1664 - Pubmed citation
- 5. Lauria MR, Gonik B, Romero R. Pulmonary hypoplasia: pathogenesis, diagnosis, and antenatal prediction. Obstet Gynecol. 1995;86 (3): 466-75. doi:10.1016/0029-7844(95)00195-W - Pubmed citation
- 6. Ohlsson A, Fong K, Rose T et-al. Prenatal ultrasonic prediction of autopsy-proven pulmonary hypoplasia. Am J Perinatol. 9 (5-6): 334-7. doi:10.1055/s-2007-999258 - Pubmed citation
- 7. Brewerton LJ, Chari RS, Liang Y et-al. Fetal lung-to-liver signal intensity ratio at MR imaging: development of a normal scale and possible role in predicting pulmonary hypoplasia in utero. Radiology. 2005;235 (3): 1005-10. doi:10.1148/radiol.2353040280 - Pubmed citation
- 8. Kasprian G, Balassy C, Brugger PC et-al. MRI of normal and pathological fetal lung development. Eur J Radiol. 2006;57 (2): 261-70. doi:10.1016/j.ejrad.2005.11.031 - Pubmed citation
- 9. Nimrod C, Davies D, Iwanicki S et-al. Ultrasound prediction of pulmonary hypoplasia. Obstet Gynecol. 1986;68 (4): 495-8. - Pubmed citation
- 10. Laudy JA, Tibboel D, Robben SG et-al. Prenatal prediction of pulmonary hypoplasia: clinical, biometric, and Doppler velocity correlates. Pediatrics. 2002;109 (2): 250-8. Pediatrics (full text) - Pubmed citation
- 11. Tanigaki S, Miyakoshi K, Tanaka M et-al. Pulmonary hypoplasia: prediction with use of ratio of MR imaging-measured fetal lung volume to US-estimated fetal body weight. Radiology. 2004;232 (3): 767-72. doi:10.1148/radiol.2323030359 - Pubmed citation
- 12. Obenauer S, Maestre LA. Fetal MRI of lung hypoplasia: imaging findings. Clin Imaging. 32 (1): 48-50. doi:10.1016/j.clinimag.2007.08.019 - Pubmed citation
- 13. Knox WF, Barson AJ. Pulmonary hypoplasia in a regional perinatal unit. Early Hum. Dev. 1986;14 (1): 33-42. - Pubmed citation
- 14. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 15. Guidelines for the prenatal diagnosis of fetal skeletal dysplasias. (2009) Genetics in medicine : official journal of the American College of Medical Genetics. 11 (2): 127. doi:10.1097/GIM.0b013e3181971ccb - Pubmed