NEURORADIOLOGY


Case 42 :

Fifty five year old female patient with chronic retro-orbital headache and right sided diminished vision and diplopia, presented for CT of head.

 

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Lateral Scannogram
Axial contrast CT section
Coronal contrast CT
Sagittal contrast CT

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Imaging Findings

There is an expansile hypodense lesion (HU values 10-25) in right sphenoid sinus with thinning of bony walls. The expansile lesion is seen to abut the apex of right orbit causing displacement of the supraclinoid right internal carotid artery. Inferiorly, the mass is seen to bulge into the nasopharynx. No calcific focus noted within the mass.

Diagnosis:
Mucocele of right sphenoid sinus.

Discussion:
Mucoceles are epithelium lined cyst-like lesions that most commonly produce bone destruction within the paranasal sinuses. Approximately 2/3rd of all mucoceles involve the frontal sinuses, followed by ethmoid and maxillary sinuses. Sphenoid mucoceles occur rarely (incidence 1%). These lesions tend to extend and expand along the path of least resistance. The slow and silent expansion of a mucocele may be unsuspected until bone is eroded and it impinges on adjacent structures.

Sphenoidal mucoceles generally tend to spread more frequently in an anterior–inferior fashion with invasion of the ethmoid, nasal fossae and the nasopharynx. It may show upward invasion with destruction of the sellar floor. There may be an invasion in the orbital cavity when spreading occurs sideways. More rarely, the middle cranial fossa is invaded through the lateral wall and the posterior cranial fossa through the posterior wall.

The most common presenting symptom is headache, which is often described as frontal/retroorbital in nature (70% of patients). Second common symptom is visual disturbances (65% of patients). Visual symptoms include diplopia, ocular muscle paresis, exophthalmus and complete visual loss. Sphenoid mucocele is a rare differential diagnosis of oculomotor nerve palsy, which is probably caused by compressing the microvascular supply to the nerve. Oculomotor nerve involvement is usually accompanied by optic nerve involvement. Rarely orbital apex syndrome may also be caused.

Imaging is important in early diagnosis because it may help prevention of the occurrence of the neurological manifestations resulting from the extension of the lesion. A large mucocele produces a classic radiographic appearance of an enlarged distorted sinus with a large bony defect due to breakthrough into the adjacent structures. On CT mucoceles are homogeneous isodense expansile mass, filling the sinus cavity and extending into the surrounding structures. After injection of contrast medium, there is no increase in the intrinsic density of mucocele due to its avascular mucoid content. However, rim enhancement may rarely occur, and it is caused by capsular inflammation or peripheral induration. CT is particularly useful in delineating the full extent of the mucocele.

MRI features of the sphenoid sinus mucocele are varying signal intensities, depending on their stage of development and protein content. Some of them have moderate or low signal intensity on T1 weighted images and a high signal intensity on T2 weighted images. They may show peripheral enhancement after administration of contrast material. Some cases show high signal intensity on both T1 and T2 weighted images. High signal intensity on T1 weighted images may be due to elevation of its protein content and viscosity. Some mucoceles may be hypointense on T2 weighted images if they contain thick mucus.



Dr Paresh Desai
Goa Medical College, Bambolim Goa
Email- mailpkd@yahoo.co.in

References:
1. Di Girolamo S, Cannizzaro P, Picciotti P, Nardi C. Ophthalmoplegia and ptosis as onset symptoms of an isolated primary mucocele of the sphenoid sinus. J Oral Maxillofac Surg 2002; 60: 1500–1502
2. Nugent GR, Sprinkle P, Bloor BM. Sphenoid sinus mucoceles. J Neurosurg 1970;
32: 443–451

3. Lim CCT, Dillon WP, McDermott MW. Mucocele involving the anterior clinoid process: MR and CT findings. AJNR Am J Neuroradiol 1999; 20: 287–290

4. H Akan , B Cihan and Ç Çelenk , Sphenoid sinus mucocele causing third nerve
paralysis: CT and MR findings,Dentomaxillofacial Radiology (2004)33,342-344