Sphenoid Mucocele

Abstract

Sphenoid mucocele is defined as the accumulation and retention of mucoid secretion within the sphenoid sinus, leading to thinning, distension, and erosion of its bony walls. Sphenoid sinus mucoceles must be differentiated from simple retentional cysts frequently observed after transsphenoidal surgery (Fig. 39.1) Several mechanisms have been proposed for the formation of mucocele: primary mucoceles can develop as retention cysts of the mucous glands of the sinus epithelium; secondary mucoceles are caused by obstruction of the sinus ostium, possibly from tumors extending inside the sphenoid sinus such as nasopharyngeal carcinoma, after trauma, radiotherapy, or transsphenoidal surgery. If impaired permeability of the antigravitational sphenoid sinus ostium seems always necessary for mucocele formation, it is probably not sufficient: an associated chronic inflammatory process, as attested by the presence of cytokines in the mucocele, constitutes a better explanation for the bone resorption and erosion phenomenon resulting in sphenoid sinus wall expansion and pseudotumoral development. Clinical features are related to mass effect, mainly headache and optic nerve compression, the latter being favored by anterior clinoid process pneumatization. Third and sixth cranial nerve palsies can also occur (Fig. 39.2) as well as chiasm compression and invasion of the pituitary fossa (Fig. 39.3). Intracranial extension caused by mucocele rupture in the subarachnoid spaces is rare (Fig. 39.4). On MRI, mucocele appears as a T1-hyperintense mass with regular contours occupying the whole or the main part of the sphenoid sinus. T1 intensity depends on the proteinic concentration and mucus viscosity. T2 signal is more variable, from hyperintense to hypointense in cases of high proteinic concentration. Concomitant aspergillosis can result in signal heterogeneity. After gadolinium injection, enhancement of the mucocele wall, but not of the mucocele itself, can be observed. Bulging or ballooning of sphenoid sinus walls is constantly observed. Diagnosis is usually easy except when the sphenoid mucocele is secondary to a sphenoid tumor. In cases of transsphenoidal surgery history, a T1WI fat-saturated sequence can be useful to differentiate fatty surgical packing from mucocele. Prevention of postsurgical sphenoid mucocele is based on excision of the sphenoid sinus mucosa and on a large sphenoidotomy to avoid mucus accumulation. Surgical treatment consists of endoscopic transnasal marsupialization (Fig. 39.5).