A rare case of mucocele confined to the right pterygoid process

Clinical History

36-year-old male patient complaining of pain in the right maxillary area. He reported a history of severe facial trauma at the age of 22. Plain film showed an opacified maxillary sinus and post-traumatic sinusitis was diagnosed. The symptoms did not improve and new symptoms like paraesthesia occurred.

Imaging Findings

Paranasal sinuses MRI was performed. It showed a round expensive mass with thin and well-defined margins, remodelling the right pterygoid process (Fig. 1, 2). The right maxillary sinus was smaller than the left but did not show further alterations (Fig 1). The mass presented homogeneous high signal in T1-weighted sequences (Fig. 1) and heterogeneous mild-low signal in T2-weighted sequences (Fig. 2). CT demonstrated a non-infiltrating homogeneous mass with very low attenuation expanding the right pterygoid process (Fig. 3) and widening of the right foramen rotundum. Some osseous fragments were noted occupying the inlet to the right pterygoid recess (Fig. 4). A normal and well-aerated left pterygoid recess on the left sphenoid sinus was present (Fig. 4).

Discussion

A presumptive diagnosis of post-traumatic pterygoid mucocele was made based on imaging findings in combination with patient's medical history.
Mucoceles are benign, slow-growing, locally expansive masses, filled with mucus and lined by epithelium. Generally they are thought to be caused by obstruction of the sinus although there are other hypotheses including cystic dilatation of glandular structures and cystic development from embryonic epithelial residues. [1] Two categories of mucoceles have been described: primary and secondary. In primary mucoceles inflammatory blockage of mucous drainage, secretory duct obstruction, cystic dilatation of mucosal glands and cystic degeneration of polyps are believed to be the underlying mechanisms. In secondary mucoceles, prior sinus surgery or trauma are considered to contribute to their formation. [2] They equally occur in men and women with the highest incidence during the third and fourth decades of life. [2]
The majority of paranasal sinus mucoceles occur in the frontal (60%) followed by the ethmoid sinus (30%). Only 10% are located in the maxillary sinuses and they are rarely found in the sphenoid sinus. [3] Aeration of the pterygoid processes potentially occurs after the closure of the spheno-occipital suture. [4] When it happens they may become involved in obstructive inflammatory disease such as sinusitis and mucocele formation. [5]
On imaging, mucoceles can be differentiated from simple fluid retention by their expansive character. [1] Signal intensity in MRI is variable depending on the stage of development, protein content and imaging parameters. [6] High protein concentration is increasing the signal intensity on T1-w images, the signal intensity on T2-w images is dependent of the water content / state of dehydration. [6]
Clinical symptoms associated with mucoceles depend on their location and size, double vision (ophtalmologic symptoms) being the most common. [2] Vision loss can result in cases of sphenoid location. [7]
Surgical drainage was performed. Abundant mucus and some osseous fragments were removed. Pathologic analysis confirmed the diagnosis.
We hypothesise that trauma resulted in the development of scar formation which subsequently blocked the drainage of secretions, being the cause for mucocele formation. The involvement of the foramen rotundum caused irritation of the maxillary branch of the trigeminal nerve with subsequent pain and paraesthesia. A false-positive diagnosis of opacified sinus on plain X-ray was caused by the presence of the mass behind the maxillary sinus.

Differential Diagnosis List

Final Diagnosis

Post-traumatic pterygoid mucocele

URL:	https://www.eurorad.org/case/15496
DOI:	10.1594/EURORAD/CASE.15496
ISSN:	1563-4086