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Neuroradiology Case of the Week

Case 84

Deepa Popuri and Leena Ketonen, MD, PhD

Clinical Presentation: The patient is a 13-year-old woman with a diagnosis of Ewing’s sarcoma status post three courses of chemotherapy.

Radiological Findings:  There is an expansile lesion in the right side of the ethmoid air cells that measures 3.7 AP x 2.9 transverse x 3.7 in height. This lesion shows significant enhancement after administration of Gadolinium. In addition there is increased secretions within the frontal sinuses related to obstruction with inflammatory changes.

Diagnosis: Ewing's sarcoma of the nasal cavity and sinuses with secondary mucocele

Discussion: 
CLINICAL DISCUSSION:
Epidemiology: Mucoceles are caused by the accumulation of mucus due to occlusion of a draining sinus ostium [1]. Mucoceles are responsible for approximately 3% cases of nonendocrine exophthalmos and 4% of orbital or sinus disease [[2].

Presentation: Patients often have a history of allergic rhinitis, sinusitis, or violent injury. Typical presentation may include headache or rhinomucorrhea. Ocular abnormalities such as exophthalmos, visual deficit, and disaxiation of eyeball may occur due to oculomotor nerve or muscle displacement [2].

Etiology: Mucoceles result from the accumulation of impacted mucus behind an occlusion of a sinus ostium; blockage may be secondary to trauma or neoplastic obstruction. Accumulation may also occur as a result of increased mucous secretions of inflamed epithelium in the sinuses [1,2].

Etiology/Pathology: Mucoceles are slow growing, benign accumulations of mucus. Accumulation of mucous occurs from most to least commonly in the frontal, ethmoid, maxillary and sphenoid sinuses; posterior fossa accumulations are less common. Mucocele may compress or distend intracranial and or intraorbital structure. Skull erosion may be evident on radiographic studies [1,2].

Treatment and Prognosis: Early detection of mucocele along with surgical intervention is optimal to avoid irreversible neurological damage. Goals of surgery include evacuation of the lesion and removal of sinus mucosa to prevent relapse. Post surgically, patients experience improvement in visual acuity and decreased exophthalmos [2].

NEUROIMAGING DISCUSSION:
Mucosal lining appears hypointense or isotense on T1 images and moderately hyperintense on T2 images with variable thickness. MRI findings within the mucocele are more variable and depend on consistency of the accumulated mucus. Solid, inspissated mucus secretions are hypointense on T1 images and even more so on T2 images. This reflects a decrease in available hydrogen protons for the resonance phenomenon, producing hypointense MR signal. CT reveals diffuse hyperdensity within inspissated mucus and no enhancement upon contrast injection. CT, then, is especially useful in identifying dehydrated mucus accumulation; this may appear as an aerated sinus in MR images if there is no sinus enlargement. Mucus with liquid consistency appears hyperintense on T1 and T2 images, reflecting high water and protein content [1,3]. This hyperintensity on MR images is useful in distinguishing fluid mucocele from isotense neoplasms [4]. CT images of fluid mucus are hypointense [1]. Mucocele may produce ring enhancement on MR images with contrast. [4]. Distension of sinus walls or compression of adjacent neurovascular structures are other possible findings in CT and MR images [2].

References:

1. Osborn A. Diagnostic Neuroradiology. St. Louis: CV Mosby, 1994.
2. Delfini R, Missori P, Iannetti G et al. Mucoceles of the paranasal sinuses: report of 28 cases. Neurosurgery 1993; 32:901-906.
3. Van Tassel P, Lee Y, Jing B, and DePena C. Mucoceles of the paranasal sinuses: MR imaging with CT correlation. American Journal of Neuroradiology 1989;10:607-612.
4. Lanzieri C, Shah M, Krauss D, and Lavertu P. Use of Gadolinium-enhanced MR imaging for differentiating mucoceles from neoplasms in the paranasal sinuses. Radiology 1991;178:425-428.