December 20, 2013 by Alireza Mohebbi, MD; Hesam Jahandideh, MD; Ali Amini Harandi, MD . Ear Nose Throat J. 2013 December;92(12):563-565.

Abstract

A 37-year-old woman presented with isolated right-sided oculomotor nerve palsy. Neurologic examination revealed no other disorder. Computed tomography of the paranasal sinuses demonstrated complete opacification of the sphenoid sinus. Dense mucoid fluid was drained from the sphenoid sinus via an endoscopic transseptal sphenoidotomy. A biopsy confirmed the diagnosis of sphenoid sinus mucocele. At follow-up 4 weeks postoperatively, the patient’s ocular symptoms were markedly alleviated. Considering rare causes of isolated oculomotor nerve palsy, such as sphenoid sinus mucocele, is important in the differential diagnosis, even in patients with well-known risk factors such as diabetes mellitus.

Introduction

Isolated palsy of the oculomotor nerve (cranial nerve III) is seen in association with neoplasms, trauma, infarctions, hemorrhages, demyelination, aneurysms, inflammations, ischemias, infections, and uncal herniations.1 Mucoceles occur as a consequence of long-standing sinusitis; they may arise when any lesion blocks the normal outflow of mucus from a sinus cavity. Symptoms occur when a mucocele impinges on surrounding structures.2

In this article, we describe a rare manifestation of a sphenoid sinus mucocele as isolated oculomotor nerve palsy in a diabetic patient. This case has important implications for the differential diagnosis of diabetic ophthalmoplegia.

Case report

A 37-year-old woman was referred to our clinic for evaluation of headache in her right frontoparietal area of 1 month’s duration and right-sided ptosis of 15 days’ duration. She reported diplopia but denied any impairment in her visual acuity. She also denied nasal obstruction, postnasal drainage, purulent discharge, and hyposmia/anosmia. She had a 5-year history of diabetes mellitus, which was well controlled with metformin. She was also taking fluoxetine for the treatment of depression. She had no other significant medical problems.

On physical examination, the patient’s blood pressure and other vital signs were normal. Her visual acuity in both eyes was 20/25, and her pupils were symmetric and reactive to light; there was no relative afferent pupillary defect. Pupil-sparing oculomotor nerve palsy was seen in the right eye, but the trochlear nerve (cranial nerve IV) and the abducens nerve (cranial nerve VI) were both intact (figure 1). Funduscopic examination detected no abnormality, and neurologic assessment revealed no deficit other than the right oculomotor nerve palsy.

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Figure 1. Preoperatively, the patient exhibits isolated pupil-sparing oculomotor nerve palsy

Computed tomography (CT) of the paranasal sinuses demonstrated complete opacification of the sphenoid sinus. Magnetic resonance imaging (MRI) of the head and paranasal sinuses showed marked intensity on T1- and T2-weighted imaging without enhancement after gadolinium injection (figure 2). The results of four-vessel CT angiography of the brain, which had been performed at another center to rule out an intracranial lesion, were normal.

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Figure 2. The sphenoid sinus mucocele is seen on T1-weighted MRI

Since the findings on imaging studies were consistent with a mucocele, we performed an endoscopic transseptal sphenoidotomy. Dense mucoid fluid was drained from the sphenoid sinus. No intersphenoid septum was present, and the anterior and inferior walls of the sinus were thinned significantly. The right lateral wall of the sphenoid sinus exhibited dehiscence in some areas. Analyses of smears and a culture of sinus fluid were negative. A biopsy confirmed the diagnosis of a sphenoid sinus mucocele.

At follow-up 4 weeks postoperatively, the patient’s ocular symptoms were markedly alleviated (figure 3).

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Figure 3. At follow-up 4 weeks after sphenoid sinus mucocele drainage, the patient shows a marked alleviation of her ophthalmoplegia

Discussion

Sphenoid sinus mucocele can occur at any time from early adulthood to 70 years of age; it occurs in men and women equally.3 Sphenoid sinus mucoceles account for only 1% of all mucoceles of the paranasal sinuses.2 To the best of our knowledge, only 140 cases of sphenoid sinus mucocele have been reported in the literature.3 However, it is likely that more cases have been missed because the presenting symptoms are nonspecific and because the physical examination is inadequate for detecting them because of the inaccessibility of the sinus.

The etiology of sphenoid sinus mucocele is still not completely understood, but three pathogenic mechanisms have been identified: submucosal edema, secretory duct obstruction, and ostia obstruction.3 Primary mucoceles occur as a result of secretory duct obstruction of a single mucous gland that leads to the formation of a mucus retention cyst. Secondary mucoceles are caused by obstruction of the natural ostium of the sinus following trauma, surgery, or inflammation. Secondary mucoceles are more common than primary mucoceles.

Symptoms occur when a mucocele impinges on surrounding structures, including cranial nerves II through VI, the dura mater, the anterior cranial fossa, the pituitary gland, the cavernous sinus, the internal carotid artery, the pterygoid canal, the pterygoid nerve, the sphenopalatine artery, and the sphenopalatine ganglion. The most common symptom of sphenoid sinus disease is headache. The headache can be nonspecific in location and quality or it can be localized to the vertex, occipital, posterior parietal, retro-orbital, or other areas of the head and face.2

The second most common symptom is vision loss secondary to the proximity of the sphenoid sinus to the orbital apex.4 Also, cranial neuropathies are seen in as many as 50% of cases; the oculomotor nerve is generally considered to be the most frequently involved nerve,5 although one series found that the abducens nerve was the most common cranial nerve involved in sphenoid pathologies, including neoplasms.2

Isolated oculomotor nerve palsies often occur as a result of the presence of a lesion within the subarachnoid space, so considering this condition in the differential diagnosis is important.1 The presence of a normal-sized and reactive pupil reduces the likelihood of an aneurysm but does not rule it out. One explanation for isolated oculomotor nerve palsy in sphenoid sinus mucocele is that the sinus expands anteriorly at the level of the anterior clinoid process where the oculomotor nerve is closest to the sinus.5 Frontal sinus mucoceles also have been reported to cause isolated oculomotor nerve palsy.6

In cases of sphenoid sinus mucocele, CT of the paranasal sinuses will reveal an expansile, homogeneous lesion with no contrast enhancement in the sinus. On MRI, the appearance of mucoceles varies because of alterations in the protein concentration of the obstructed mucoid secretions; however, the mass may be hyperintense on all sequences of MRI.7

Ischemic oculomotor nerve palsy, also called diabetic third-nerve palsy, is the most common etiologic subset of oculomotor nerve palsy in adults.1 Its pathogenesis is believed to be microvascular in nature; hypertension and advanced age are risk factors. Although some cases of isolated ischemic oculomotor nerve palsy are caused by a midbrain infarction, most are due to peripheral ischemia.1 In our case, the patient’s known history of diabetes, her headache, and the pupil-sparing pattern of her oculomotor nerve palsy could have been erroneously interpreted as diabetic third-nerve palsy. Hence, the importance of clinical suspicion and appropriate imaging cannot be overemphasized.

The treatment of sphenoid sinus mucocele is surgical drainage, preferably via an endoscopic approach.3 Fluid encountered at the time of surgery is commonly viscid and gray-green, brown, or yellow. It is usually sterile; in rare cases, mixed anaerobic organisms are found.2 Treatment usually results in rapid regression of the ophthalmic manifestations,5 as occurred in our case.

References

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  2. Grillone GA, Kasznica P. Isolated sphenoid sinus disease. Otolaryngol Clin North Am 2004; 37 (2): 435-51.
  3. Soon SR, Lim CM, Singh H, Sethi DS. Sphenoid sinus mucocele: 10 cases and literature review. J Laryngol Otol 2010; 124 (1): 44-7.
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