Imaging appearance of dextranomer/hyaluronic acid copolymer implant injections for treatment of velopharyngeal insufficiency

Abstract

Background and purpose: Dextranomer/hyaluronic acid copolymer implants are used in treating velopharyngeal insufficiency. These posterior nasopharyngeal implants can be mistaken for pathologic conditions such as retropharyngeal abscess on imaging. We studied the imaging appearance of dextranomer/hyaluronic acid copolymer implants in patients treated for velopharyngeal insufficiency.

Materials and methods: A consecutive series of patients with velopharyngeal insufficiency treated with dextranomer/hyaluronic acid copolymer were included in this study. Data on patient characteristics and volume of dextranomer/hyaluronic acid copolymer injected were obtained. Postoperative imaging characteristics on plain radiography, CT, and MR imaging were assessed. The imaging appearance of postoperative complications was determined.

Results: Sixteen patients were included in this study. Seven patients underwent postoperative plain radiographs, 5 patients underwent CT, and 9 patients underwent MR imaging. Plain radiographs demonstrated soft-tissue swelling in the retropharyngeal space, which resolved at 1 month. On CT, dextranomer/hyaluronic acid copolymer implants appeared as bilateral nasopharyngeal soft-tissue masses isoattenuated to hypoattenuated relative to muscle in 80% (4/5) of patients. On MR imaging, dextranomer/hyaluronic acid copolymer implants appeared as bilateral nasopharyngeal soft-tissue masses that were isointense to muscle on T1 (8/9, 88.9%) and hyperintense to muscle on T2 (8/9, 88.9%) and demonstrated no restricted diffusion (4/4, 100.0%) or peripheral enhancement (7/7, 100.0%).

Conclusions: The normal postoperative findings of posterior nasopharyngeal dextranomer/hyaluronic acid copolymer injection on MR imaging is characterized by the presence of bilateral nasopharyngeal soft-tissue masses that are isointense to muscle on T1 and hyperintense on T2, with no restricted diffusion or peripheral enhancement. Velopharyngeal dextranomer/hyaluronic acid copolymer implants are iso- to hypoattenuated to muscle on CT and are not visible radiographically once associated implantation-related swelling has resolved.

Fig 1.

Postoperative radiographs following dextranomer/hyaluronic acid copolymer injection. Images obtained at 2 days (A) and 3 months (B) post-dextranomer/hyaluronic acid copolymer injection demonstrate soft-tissue swelling at 2 days posttreatment (A) and no soft-tissue swelling on the 3-month radiograph (B).

Fig 2.

Normal imaging characteristics of dextranomer/hyaluronic acid copolymer injections on CT. A, Contrast-enhanced CT in a 56-year-old woman 2 months postinjection of dextranomer/hyaluronic acid copolymer. The white arrow points to a small amount of hypoattenuated fluid in the retropharyngeal space consistent with the injection site. B, Noncontrast CT in a 3-year-old boy 3 months status post dextranomer/hyaluronic acid copolymer injection. Hypoattenuation in the right retropharyngeal space (white arrow) indicates the implant. Sagittal images of the patient better demonstrate the hypoattenuation corresponding to the implant (C). D, Contrast-enhanced CT in a 53-year-old woman 9 months post dextranomer/hyaluronic acid copolymer injection demonstrates hypoattenuation in the retropharyngeal space consistent with the implant.

Fig 3.

Retropharyngeal abscess 8 months after dextranomer/hyaluronic acid copolymer injection in a 68-year-old man. Retropharyngeal abscess following dextranomer/hyaluronic acid copolymer injection demonstrates mild peripheral enhancement on contrast-enhanced CT (A), internal T2 hyperintensity (B), and mild T1 hyperintensity (C). There are areas of restricted diffusion within the abscess seen on the DWI (D) and ADC (E) images. Peripheral enhancement on postgadolinium echo-spoiled gradient echo is demonstrated as well (F).

Fig 4.

Normal imaging characteristics of dextranomer/hyaluronic acid copolymer injection on MR imaging. MR images in a 71-year-old man status post dextranomer/hyaluronic acid copolymer injection demonstrate a multiloculated T2 hyperintense (A) and T1 isointense lesion (B) on axial images. DWI (C) and ADC (D) images demonstrate no evidence of restricted diffusion. MR images in a 13-year-old girl 1 month status post injection demonstrate a multiloculated T2 hyperintense (E) and a T1 isointense lesion on axial images (F). No evidence of peripheral enhancement is seen on postgadolinium T1-weighted images (G). No evidence of restricted diffusion (H) is seen.

Fig 5.

MR imaging characteristics of an ex vivo sample of dextranomer/hyaluronic acid copolymer compared with water. T2 imaging by using a water vial (A) and a vial of dextranomer/hyaluronic acid copolymer solution (B) demonstrates that the dextranomer/hyaluronic acid copolymer solution is hyperintense with a signal intensity similar to that of water. T1 imaging by using a water vial (C) and a vial of dextranomer/hyaluronic acid copolymer (D) demonstrates that the dextranomer/hyaluronic acid copolymer solution is hyperintense to water.