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Neuroradiology Case of the Week

Case 110

Sarah Goldfeder and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: The patient is a 19-year-old female with a past medical history significant for morbid obesity who presented with a history of headaches for six weeks, as well as nausea and vomiting. She was initially evaluated for suspicion of brain tumor, pseudotumor cerebri, and venous sinus thrombosis.

Radiological Findings: MRI of the head revealed a 14x18 mm right sphenoid sinus cystic lesion with scalloping of adjacent bone in clivus. Otherwise, the head MRI was normal. MRA and MRV of the head were both normal. MRI and MRA of the neck were both normal.
     CT facial showed a right ethmoid low density mass with mild bowing of the clivus posteriorly without evidence of destruction or osseous erosion. The left sphenoid sinus and remaining paranasal sinuses were within normal limits.

Diagnosis: Mucocele of the right sphenoid sinus.

Discussion: A sinus mucocele is defined as a mucous collection lined by the mucous-secreting epithelium of a paranasal sinus. It occurs when a sinus ostium or a compartment of a septated sinus becomes obstructed, thus causing the sinus cavity to be mucous-filled and airless. The obstruction is often inflammatory in nature, but may also be due to tumor, trauma, or surgical manipulation. It is the most common expansile lesion of the paranasal sinuses and leads to outward expansion with bony remodeling. Initially, the bony structures remain intact, but with further expansion, deossification may occur. If outward expansion is not identified, then the sinus is considered to be an obstructed sinus, as opposed to one containing a mucocele. Sixty to 65% of mucoceles reside in the frontal sinuses, 20 to 25% in the ethmoid sinuses, 5 to 10% in the maxillary sinuses, and 5 to 10% in the sphenoid sinuses.
     While a retention cyst is also defined as a mucous collection lined by mucous membrane, it differs from a mucocele in the following ways. A retention cyst forms when a mucous gland of the sinus mucosa becomes obstructed. Its walls are thus defined by the epithelium of a mucous gland and duct itself, not by the walls of the sinus. There is almost always air still surrounding the retention cyst, and bony expansion and remodeling of the sinus does not often occur. They are most commonly found within the maxillary sinus and are incidental findings in at least 10% of people.
     Signs and symptoms of a mucocele may last from a few days to years and are most often due to mass effect. A mucocele in the frontal sinuses typically leads to frontal headaches and inferolateral proptosis with diplopia. Additionally, a superomedial orbit mass may develop, and the voice may be nasal in quality. A mucocele in the ethmoid sinuses frequently presents as lateral proptosis as well as nasal congestion. A mucocele in the maxillary sinuses causes upward displacement of the eye, a cheek mass, and nasal congestion. A mucocele in the sphenoid sinuses can lead to suboccipital headaches and visual loss. While mucoceles are usually sterile in nature, pain may indicate infection. An infected mucocele, or mucopyocele, may have ring enhancement.
     On CT, a mucocele presents as a nonenhancing, homogeneous, and hypodense mass that fills and expands the entire sinus cavity. Its appearance on MRI varies depending on the protein concentration, which changes over time.  On contrast-enhanced MRI, the sinus mucosa enhances as a thin line surrounding the mucocele.
     The recommended treatment of most mucoceles is surgical marsupialization, through endonasal endoscopic surgery. This approach is minimally invasive and preserves sinus architecture.

References:

1. Som and Curtin: Head and Neck Imaging, 4th ed., Volume One. 2003 Mosby: 204-230, 838-840.
2. Cummings: Otolaryngology: Head and Neck Surgery, 3rd ed., 1998 Mosby-Year Book, Inc: 1084, 1115-1116.
3. Serrano E, Klossek JM, Percodani J, Yardeni E, Dufour X.  Surgical management of paranasal sinus mucoceles: a long-term study of 60 cases. Otolaryngology—Head and Neck Surgery.  2004. 131(1): 133-140. [Medline]