Congenital peribronchial myofibroblastic tumor: prenatal imaging clues to differentiate from other fetal chest lesions
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- Calvo-Garcia, M.A., Lim, F., Stanek, J. et al. Pediatr Radiol (2014) 44: 479. doi:10.1007/s00247-013-2817-8
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We present a prenatal case of congenital peribronchial myofibroblastic tumor referred as a congenital pulmonary airway malformation (CPAM) with hydrops and polyhydramnios at 30 weeks’ gestational age. US and fetal MRI findings did not fit with the referral diagnosis, raising the possibility of intrinsic lung tumor. Fetal hydrops worsened and the baby was successfully delivered by ex utero intrapartum treatment (EXIT) to resection at 31 weeks’ gestational age. To the best of our knowledge, this is a unique case of congenital peribronchial myofibroblastic tumor that underwent comprehensive prenatal evaluation and EXIT procedure with good outcome.
KeywordsCongenital peribronchial myofibroblastic tumorLungPrenatal diagnosisFetal MRISonography
Congenital peribronchial myofibroblastic tumor is a congenital lung tumor with benign histology. The lesion typically presents as a large solid lung mass associated with hydrops in the fetal or neonatal period . Fourteen cases have been reported in the literature, with only two providing a description of prenatal imaging findings [2, 3]. We report the US and fetal MRI characteristics of this tumor, characteristics that are dissimilar to common fetal chest lesions. The implications of this diagnosis in the management of the pregnancy are described.
The mother was a healthy 20-year-old gravida I para 0 who had a prenatal sonogram at 29 weeks’ gestational age interpreted as solid-type congenital pulmonary airway malformation (CPAM) with hydrops and polyhydramnios. Prior first-trimester US examination was unremarkable. She had an amnioreduction, received a course of betamethasone and was referred to our institution.
After resection of the tumor the baby boy was placed on ventilatory support but did not require extracorporeal membrane oxygenation. He sustained the expected respiratory distress and persistent pulmonary hypertension from significant prematurity and pulmonary hypoplasia. The hydrops resolved and the pulmonary hypertension improved over the next 4 weeks. The baby remained intubated for 5 weeks and was weaned to oxygen support via nasal cannula at 6 weeks of age. A contrast-enhanced CT of the chest and abdomen performed at 7 weeks, prior to discharge, showed no residual tumor or metastatic disease. He was weaned off oxygen before 3 months of age. At 17 months, he was doing well, growing adequately and without any respiratory symptoms on room air.
Developmental lung malformations, mediastinal tumors such as teratoma, and chest wall lesions such as mesenchymal hamartoma are common chest lesions in the perinatal period. Congenital lung tumors are rare and might not be considered in the initial differential diagnosis of a fetal chest mass . However in analyzing the imaging characteristics of this mass, we noticed that it did not follow the typical pattern described for solid-appearing developmental malformations that would include microcystic-type CPAM, pulmonary sequestration/hybrid lesion and congenital lobar overinflation. On US the lesion was not hyperechoic, and on fetal MRI it was not T2 hyperintense and T1 hypointense to normal lung. In addition there was no systemic feeding vessel, as expected for a bronchopulmonary sequestration or a hybrid lesion. Even though these bronchopulmonary malformations can demonstrate decreased conspicuity during the third trimester, our case was atypical in that the mass was not shaped like a lung lobule and instead presented with well-defined margins and an ovoid shape . We also excluded other considerations. There was no chest wall deformity or complex cystic component with fluid-fluid levels to suspect a mesenchymal hamartoma of the chest wall. A mediastinal teratoma was not considered because the lesion was not located in the anterior mediastinum or pericardium and subsequently there was no posterior-inferior displacement and compression of the heart.
Primary lung tumors that typically present in the perinatal period include congenital peribronchial myofibroblastic tumor, cystic type I pleuropulmonary blastoma, fetal lung interstitial tumor and congenital-infantile fibrosarcoma [6, 7]. Congenital peribronchial myofibroblastic tumor is a rare benign mesenchymal tumor that is usually detected during the fetal and neonatal period. Of these primary lung tumors, congenital peribronchial myofibroblastic tumor is the only neoplasm that has been reported as early as in the second trimester . Congenital peribronchial myofibroblastic tumor typically presents as a large solid chest mass with hydrops fetalis, potentially leading to intrauterine fetal demise or respiratory distress at birth. In the absence of hydrops or prematurity, the lesion has a good prognosis after resection without need for adjuvant therapy. The tumor is thought to arise from the pluripotent mesenchyme found around proximal bronchial branches at 12 weeks of development. Histology shows proliferation of uniform myofibroblasts around a bronchus with invasion into surrounding lung parenchyma and negative histochemical staining for smooth muscle elements. The first cases described in the literature were incorrectly classified as malignant and low-grade sarcomas and were reported under a variety of names, including bronchopulmonary leiomyosarcoma, bronchopulmonary fibrosarcoma, congenital fibroleiomyosarcoma, hamartoma and congenital mesenchymal malformation. McGinnis and colleagues  provided the present accepted nomenclature in agreement with its benign nature and postulated origin. Our case is consistent with a previous report of congenital peribronchial myofibroblastic tumor in which the mass was described on prenatal US as a spherical, hypoechoic lesion relative to the fetal lungs and with internal flow . In addition we noticed punctate foci of increased echogenicity throughout the lesion. This heterogeneous internal echotexture could reflect the architecture of the mass on pathological analysis. The tumor has a trabeculated appearance on cut surface, corresponding to broad intersecting fascicles of tumor cells along the interlobular septa and bronchovascular bundles intermixed with entrapped lung tissue on microscopy (Figs. 3 and 4). We also defined the signal characteristics of the mass compared to the adjacent and contralateral normal lung on both T2-W and T1-W images. These characteristics had not been reported, and although they are not entirely specific they would support a solid fibrous tumor such as congenital peribronchial myofibroblastic tumor. The tumor had no capsule to explain the thin rim of dark T2 signal noted around the mass. However, this finding could be related to compression and displacement of adjacent lung and blood vessels and the presence of focal fibrous tissue observed at the periphery of the tumor (Fig. 4). Congenital infantile fibrosarcoma would present as a solid mass and would be considered in the differential diagnosis in our patient. However it is most typically found involving the soft tissues and rarely the lung . Imaging characteristics were not suggestive of other congenital lung tumors. Pleuropulmonary blastoma was not considered in this case because the lesion was not cystic and its solid form had not been seen at this age. Fetal lung interstitial tumor is a recently described congenital pulmonary tumor with a solid or mixed cystic appearance ; the only prenatally reported imaging example of this tumor was a solid echogenic mass with hyperintense T2 signal compared to adjacent lung, which was inconsistent with the findings in our patient.
The implications of this diagnosis are important. Had it been recognized that the mass was not a CPAM at the time of workup, it would be have been known that the lesion would not respond to steroids. In addition, counseling would include information with regard to open fetal surgery or EXIT-to-resection delivery in the setting of hydrops and expected prematurity. Fetal surgery allowed survival in a prior case detected in the second trimester with successful progression of the pregnancy to 35 weeks of gestational age . Our patient was delivered at 31 weeks of gestational age and is the youngest surviving premature infant in the presence of such a large congenital peribronchial myofibroblastic tumor and fetal hydrops at birth. Successful resection of the tumor on placental support allowed a more controlled transition of this high-risk fetus from the in utero environment to the postnatal ward. The relatively low lung volume noted prenatally was from a combination of parenchymal compression and non-lethal lung hypoplasia, explaining the clinical course of our patient after surgery and further supporting the importance of our planned approach.
In summary, with this case we present the complete prenatal imaging assessment of this rare but quite specific neonatal lung tumor, supported by pathological analysis. Appropriate recognition of congenital peribronchial myofibroblastic tumor is critical in the clinical management of the pregnancy and postnatal period and should be considered when a large solid fetal lung mass is detected.
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