eRadiograph Volume 7: Imaging of Oral Cavity | Page 291

Primary lesion of the RPS are rare, most lesions seen in the RPS are due to spread from adjacent spaces or metastases. Lipomas These are the most common primary tumor seen as an oval shaped elongated fat density lesion conforming to the shape of the retropharyngeal space. On CT it appears hypodense, on MRI T1W1 hyperintense, with its signal suppressed on fat suppressed images. Rarely a liposarcoma may be seen. These demonstrate more than 25 % non fat density/intensity tissue which may be nodules, thick septa or have marked enhancement of septae and nodules. Direct Spread of Neoplasm to RPS Nasopharyngeal carcinoma is limited by the pharyngobasilar fascia, however once it breaches the fascial plane it extends into the RPS and from the RPS it may extend to involve skull base or extend intracranially directly or via perineural spread. Supraglottic oropharyngeal, sinonasal tumors may also grow into RPS extending into a craniocaudal direction after gaining access because there are no fascial barriers within the RPS. Thyroid goiters may also extend posteriorly and medially into the RPS. Primary lesions of the spine chordoma can invade prevertebral space and then RPS extending anteriorly. Rarely congenital branchial cleft cysts, foregut duplication cysts, ectopic parathyroid adenoma or hyperplasia may occur in the retropharyngeal space. Following radiation therapy for nasopharyngeal/oropharyngeal CA there may be fluid in the retropharyngeal space. This fluid is reactionary and does not cause bulging of the fascial margins as a retropharyngeal abscess would. These reactionary collections appear 4-6 weeks after radiation and disappear 8-10 weeks after radiation. The differentiation between a lesion in RPS and in the prevertebral space is based on the displacement of the prevertebral muscles if they are displaced anteriorly prevertebral space lesion if displaced posteriorly RPS lesion. 291 Retropharyngeal Space Nodal metastases from SSC: Squamous cell carcinoma of the oropharynx /nasopharynx may metastasize to the nodes in the RPS particularly if there is posterior pharyngeal wall involvement.