Direct Extension: Types II and III PPB may metastasize within or beyond the chest cavity. Within the chest, there may be implantation and invasion of all pleural surfaces, lung parenchyma, and diaphragmatic muscle. Hilar and mediastinal node involvement occurs but is distinctly unusual.
Embolic Spread: PPB invades great vessels in the thorax, including both right and left circulations. The Registry is aware of 8 Registry and literature cases of great vessel invasion and/or embolic spread. Superior vena cava syndrome is reported, although SVC syndrome can also occur from massive chest disease without SVC invasion. In some cases, vascular invasion is known by vascular ultrasound studies. Embolism has been inferred from cerebrovascular infarctive and hemorrhagic events within hours to days after chest surgery in several cases. Femoral artery embolism has been pathologically documented in one case. Any suggestion of vascular compromise at presentation should be investigated by vascular studies, as in Wilms tumor. [See Tan et al. Pleuropulmonary blastoma with a large embolic cerebral infarct. Pediatr Radiol 2003;33:506-8.]
Example of PPB Tumor Embolism and Post-Operative CVA
Hematogenous metastasis: Recurrent disease often includes hematogenous spread. It is rare to have distant spread at diagnosis. The common sites of metastasis are as follows:
Analysis of Registry and several literature cases of metastases reveal the following incidence data: (aggregate data unpublished)
A PPB Registry study of 39 cases of cerebral metastases (submitted in 2005 for publication) shows that cerebral metastases are statistically more common in Type III PPB than Type II PPB. Life-table estimates of the cumulative probability at 5 years from diagnosis for cerebral metastasis is 54% for a Type III patient (95% confidence interval (CI): 31-76%) and 11% for a Type II patient (95% CI: 2-20%). These findings lead the Registry to suggest surveillance head MR scans in Type II and III PPB every 3 months until 36 months after PPB diagnosis. Cerebrospinal fluid monitoring is not suggested (see next paragraph). The frequency of cerebral metastasis in PPB is much higher than other pediatric sarcomas (typically 3 – 7%).
Metastasis to contralateral or ipsilateral lung also occurs somewhat frequently. Rare cases of metastasis to the globe (choroid), iris, bone marrow, ovary, and adrenal have been reported. Leptomeningeal disease has been seen very rarely, and paralysis from a cord or bony canal lesion (with negative CSF cytology) has occurred. Spinal cord metastases have been documented. The rare cases of marrow metastasis stand out because marrow sampling by aspiration and trephine has been carried out in numerous literature and Registry cases without finding disease. [see PubMed or Google Scholar: marrow: Kusafuka et al. p53 gene mutations in pleuropulmonary blastomas. Pediatr Hematol Oncol 2002;19(2):117-28.; iris: Lallier et al. Pleuropulmonary blastoma: a rare pathology with an even rarer presentation. J Pediatr Surg 1999;34(7):1057-9.; globe: Di Tullio et al. Pleuropulmonary blastoma: survival after intraocular recurrence. Med Pediatr Oncol 1999;33(6):588-90.; paralysis: Holland-Moritz RM, Heyn RM. Pulmonary blastoma associated with cystic lesions in children. Med Pediatr Oncol 1984;12(2):85-8.; cord mets: Selle B et al. Das pulmonale blastom im kindesalter-eine kasuistik und eine ubersicht uber die literatur Z Kinderchir 1987;42(6):373-7.]
Example of Cerebral Metastases in PPB
Example of Cerebral Metastases in PPB (following earlier embolic stroke)
This cerebral metastasis became symptomatic and was diagnosed approximately one year after the initial post-operative embolic infarct. See earlier photo. Registry Case #118. (See Tan Kendrick A. Cerebral metastasis proven 1 year after an embolic cerebral infarct from pleuropulmonary blastoma [Letter to the Editor]. Pediatr Radiol 2004;34(3):283.Courtesy of Dr Anne Tan Kendrick.)
Time to metastasis: Most PPB metastases occur within 24 months from diagnosis - occasionally out to 36 months and beyond. The following illustrates the time distribution of brain metastases in months from diagnosis (unpublished data on Registry and literature cases):