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Neuroradiology Case of the Week

Case 93

Igor Mikityansky, MD and P-L Westesson MD, PhD, DDS

Clinical Presentation - Patient 1: A 52-year-old female presented with headache and diplopia.

Radiological Findings - Patient 1: A non-contrast enhanced CT demonstrates mucosal edema in the left ethmoid, maxillary, frontal and sphenoid sinuses. There is an erosion of the floor of the left frontal sinus with mucocele protruding into the orbit and causing left eye depression and minimal exophthalmos. There is also an erosion of the superior part of the posterior wall of the left frontal sinus without any evidence of perforation. The mucocele measures 2.5x 2.6x2.2 cm.

Clinical Presentation - Patient 2: A 60-year-old male presented with headache and diplopia.

Radiological Findings - Patient 2: A contrast enhanced MRI demonstrates a ring-enhancing lesion arising from the left frontal sinus that has low-signal on T1, intermediate signal on T2, high-signal on diffusion weighted imaging, and low-signal on apparent diffusion coefficient mapping. The lesion measures 6.0x 3.2x4.0 cm. There is expansion of the lesion roof of the orbit causing anterior displacement of the left eye. It also exerts mass effect against anterior and posterior walls of the left frontal sinus with a large bony defects and displacement of the left frontal lobe posterior-superiorly.

Diagnosis: Frontal mucocele

Discussion: Mucocele is an epithelial lined mucus-containing sac completely filling a paranasal sinus and capable of expansion by virtue of a dynamic process of bone resorption and new bone formation [1]. They are benign lesions that occur with similar frequency in adults of both sexes, 20 to 60 year-old [2].
     An ostial obstruction caused by an inflammatory scar, trauma, or tumor has been suggested as a pathogenesis of mucoceles. The frontal sinuses are most commonly affected, comprising up to 65% of all mucoceles. They are followed by ethmoid sinus mucoceles, presenting in about 25% of cases, and maxillary in 10% [3].
     Symptoms and signs of frontal mucoceles include pain, swelling, exophthalmos, diplopia, and loss of vision. An erosive mucocele may lead to meningitis, meningoencephalitis, pneumocephalus, brain abscess, seizures or CSF fistulas [2].
     On plain film examination, the density of a frontal sinus mucocele is greater than that of an aerated sinus, but never greater than that of the adjacent normal frontal bone. If the sinus density is greater than the adjacent calvarium, a fibro-osseous-type lesion rather than a mucocele should be considered [4].
     CT demonstrates an airless, mucoid density (10–25 HU) filled, expansile, non-enhancing sinus mass with gradual thinning and erosion of the bony margins. Frontal sinus mucoceles tend to erode posterior wall because of its inherent thinness. The density of sinus contents of a mucocele may be low or mixed relative to that of muscle [3, 4].
     MR exhibits variable signal intensities on both T1- and T2-weighted images, depending on the state of hydration, protein content, and viscosity of the contents of the mucocele. The two most frequently observed patterns are (1) moderate-to-marked high-signal intensity on both T1- and T2-weighted images, and (2) moderate-to-marked low-signal intensity on both T1- and T2-weighted images. Contrast-enhanced MR imaging is useful in differentiating mucoceles from sinonasal tumors. Mucoceles characteristically reveal a thin peripheral linear enhancement with central low-signal intensity on T1 weighted images. Sinonasal tumors, on the other hand, demonstrate diffuse enhancement [3].
     Differential diagnosis includes paranasal sinus carcinoma, Aspergillus infection, chronic infection, inverting papilloma [5].
     The most common treatment modality is radical extirpation of the mucocele, cranialization of the sinus and nasofrontal duct obliteration using gelfoam, muscle graft and fibrin glue through a transcranial access when the posterior wall of the frontal sinus is eroded and the dura is involved. In the cases with infiltrated dura and intradural invasion of the mucocele, resection of the involved dura and duraplasty using pericranium or galea graft and fibrin glue is used. Vascularized local flaps using pericranium or galea graft are highly effective in preventing contamination of the anterior fossa. The residual defects of the anterior wall must be reconstructed with autologous bone or alloplastic materials [2].

References:

1. Gavioli C, Grasso DL, Carinci F, Amoroso C, Pastore A. Mucoceles of the frontal sinus: Clinical and therapeutical considerations. Minerva Stomatol 2002 Sep;51(9):385-90.
2. Suri A, Mahaparta AK, Gaikwad S, Sarkar C. Giant mucoceles of the frontal sinus: a series and review. J Clin Neurosci. 2004 Feb;11(2):214-8.
3. Rao VM, Sharma D, Madan A. Imaging of frontal sinus disease: concepts, interpretation, and technology. Otolaryngol Clin North Am 2001 Feb;34(1):23-39.
4. Taveras and Ferrucci’s. Radiology on CD-ROM. LW&W; 2003:V3, Chapter 12.
5. Danhert W. Danhert’s Electronic Radiology Review. W&W, 1998.