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
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