Ossifying fibromas of the paranasal sinuses: diagnosis and management

Abstract

Fibro-osseous benign lesions rarely affect the sinonasal tract and are divided into 3 different entities, namely osteoma, fibrous dysplasia and ossifying fibroma. They share several clinical, radiological and histological similarities, but have different behaviours. Ossifying fibroma, and in particular the "juvenile" histological subtype, may have a locally aggressive evolution and a high risk for recurrence if removal is incomplete. The purpose of the present study is to compare the clinical behaviour of ossifying fibroma with the other benign fibro-osseous lesions; highlight different behaviour between the histological subtypes; compare the advantages, limitations and outcomes of an endoscopic endonasal approach with reports in the literature. We retrospectively reviewed 11 patients treated for sinonasal ossifying fibroma at a tertiary care centre. All patients underwent CT scan, and MRI was performed in cases of cranial base involvement or recurrence. Pre-operative biopsy was performed in cases where it was possible to use an endoscopic approach. One patient underwent pre-operative embolisation with ipsilateral visual loss after the procedure. Depending on its location, removal of the tumour was performed using an endoscopic (n = 7), or an external (n = 3) or combined (n = 1) approach. Histopathologically, 5 patients presented the conventional type, 5 the juvenile psammomatoid variant, which was associated in 1 case with an aneurismal bone cyst, and 1 case presented the trabecular juvenile variant. Three patients affected by the juvenile psammomatoid histological variant presented invasion of the skull base and underwent a subtotal removal that subsequently required, due to the regrowth of the remnant, a transbasal approach. Clinical, radiological and histological findings should all be considered to establish differential diagnosis among fibrous osseous lesions. More studies are necessary to conclude if the localisation and extension of the disease at the time of diagnosis is more important than the histological variant. An endoscopic approach is the first choice in most of cases even if an external open approach may be necessary in selected patients.

Keywords: Endoscopic surgery; Fibrous dysplasia; Ossifying fibroma; Osteoma; Skull base.

Fig. 1.

Axial CT: OF appears as a lesion with well-defined margins showing a hypodense signal corresponding to fibrous tissue (arrowhead) with intralesional foci of hyperdensity corresponding to areas of mineralisation (arrow).

Fig. 2.

Axial MRI: on T1-weighted sequences (A) OF appears as a lesion with intermediate signal intensity, fibrous tissue (arrowhead) with small areas of hypointensity osseus areas (arrow). On T2-weighted sequences (B), ossified areas appear with low signal (arrow), while fibrous tissue exhibits an isointense signal (arrowhead). Contrast enhancement (C) is heterogeneous and is related to fibrous areas (arrow).

Fig. 3.

On T2-weighted sequences, a multicystic lesion with "fluid-fluid" levels (arrow) suggestive for ABC is present within OF .

Fig. 4.

(A) Pre-operative coronal CT scan showing the tumour at the level of the left ethmoid sinus and (B) at the level of the sphenoid. (C) Endoscopic view of the OF appearing as a submucosal mass. (D) Post-operative coronal CT scan at the level of the ethmoid sinus and sphenoid sinus.

Fig. 5.

(A) Pre-operative coronal CT of case #10 who underwent a subtotal removal of the lesion with an endoscopic approach. (B) Coronal CT scan performed 6 months after surgery showing rapid regrowth of the remnant (arrow). An external approach was subsequently performed.

Fig. 6.

Endoscopic view of OF at the level of the right nasal fossa presenting with its typical aspect: a submucosal smooth rounded mass.