Although most conditions of the frontal sinus requiring surgery can be treated endoscopically, endoscopic surgery will not be successful if long-term stable drainage is not established. An external approach may be necessary in cases where endoscopic approaches fail. The osteoplastic flap procedure with frontal sinus obliteration is the time-honored approach in such cases. Indications for osteoplastic flap with obliteration include: chronic frontal sinusitis refractory to endoscopic surgery, mucopyocele, severe trauma with fractures involving the drainage pathways, and after resection of large frontal tumors near the frontal recess . The frontal sinus outline is marked using a template from a 6 ft. Caldwell radiograph. Osteotomies are performed and the sinus is opened. The mucosa of the sinus is completely removed and the frontal recess is occluded. The sinus is filled with an autologous fat graft and soft tissue and the bony flap is replaced. The postoperative CT and MR appearances of this procedure are highly variable due to the spectrum of tissues that may be present within the sinus. Tissues may include fat, chronic inflammatory changes, retained secretions, granulation tissue, and fibrosis. MR may be of limited utility in distinguishing symptomatic patients with recurrent disease from asymptomatic patients with imaging findings related to scar tissues. Imaging is useful for early detection of postoperative mucocele formation.

Diagram demonstrating packing of the right frontal sinus after unilateral obliteration procedure. The mucosa is completely removed and the frontal recess permanently occluded.	Coronal CT image after left frontal sinus obliteration demonstrating predominantly fat density packing material within the sinus. No residual air remains in the sinus. Prior trephination defect (arrow) is noted inferiorly.	Soft tissue (A) and bone window (B) CT images after bilateral frontal sinus obliteration shows mixed, but predominantly fatty material filling the lumen of the sinuses. This patient had failed to clear the frontal sinuses after previous modified Lothrop (Draf III) procedure. The frontal drainage pathways are now filled with packing material.
Coronal (A) and axial (B) scans in an asymptomatic patient who underwent left frontal sinus obliteration after extensive traumatic injury to the face and calvarium. Fractures of the nasoethmoid complex resulted in scarring at the left frontal recess and subsequent obstruction of the sinus. Patency of the recess could not be achieved endoscopically so the sinus was obliterated. In this case the material within the sinus is predominantly soft tissue density on CT.
MR images in a 38 year old female after bilateral frontal sinus obliteration with osteoplastic flap procedure. Sagittal T1 (A) and axial T1 (B) weighted images show mixed signal intensity within the obliterated sinuses. Foci of high T1 signal consistent with fat packing (arrows) are noted. Post-gadolinium axial T1 image with fat saturation technique (C) shows suppression of signal from the fat noted in images A & B. No appreciable enhancement is seen within the obliterated sinus.
Axial MR images in a 45 year old male 2 years after bilateral frontal sinus obliteration with osteoplastic flap. Axial T1 image (A) demonstrates predominantly intermediate signal material within the sinuses with few foci of fat (arrows). On the T2 weighted image (B) the material is of increased signal compared to the subcutaneous fat. After gadolinium administration (C), there is heterogeneous enhancement throughout the obliterated sinuses. Although there is no evidence for expansion of the sinuses to suggest mucocele formation, the MR findings were somewhat concerning for recurrent disease. The patient did not have symptoms referable to the sinuses at the time of imaging. The MR imaging features in asymptomatic patients after osteoplastic flap with obliteration can be somewhat misleading.