A sinus mucocele is a dilated, epithelial-lined cystic lesion containing encapsulated mucus [1]. Although its etiology remains uncertain, secondary infection may transform it into a pyocele. COVID-19 has been suggested to be associated with opportunistic sinus infections, including multidrug-resistant bacterial or fungal pathogens. This increased susceptibility has been examined in relation to COVID-19–associated immune dysfunction and the widespread use of antibiotics and steroids during the pandemic [2–7]. The clinical manifestations of mucoceles vary depending on their location and the extent of invasion, and in some cases may mimic complications related to COVID-19 infection or vaccination [8,9]. We report the case of a 68-year-old female patient who experienced a rapid exacerbation of symptoms during a COVID-19 infection, presenting with an ethmoid sinus mucocele that manifested as ophthalmoplegia, ptosis, and blurred vision.

A 68-year-old female patient presented with an acute three-day history of left-eye ptosis, severe visual impairment, and ophthalmoplegia. One week prior to admission, she had received nirmatrelvir/ritonavir (Paxlovid) following a confirmed COVID-19 infection. Upon initial presentation to the neurology department, she was diagnosed with optic neuritis and treated with intravenous methylprednisolone (1 g/day for four days). Her medical history was notable only for hypertension and hyperlipidemia, with no prior history of trauma, sinus surgery, or other rhinologic disease.

Physical examination confirmed ptosis and significant ocular movement disorders in the left eye (Fig. 1). Visual acuity assessment revealed severe visual disturbance in the left eye, with measurements of 0.3 in the right eye and hand motion in the left eye. Although pupil size and the direct light reflex were normal, a relative afferent pupillary defect was observed in the left eye. Optical coherence tomography, fundoscopy, slit-lamp examination, Ishihara test, and tonometry revealed no specific abnormalities, and no abnormal findings were identified on examination of the other cranial nerves. Nasal endoscopy initially demonstrated no specific abnormalities, apart from a small amount of mucoid discharge in both nasal cavities (Fig. 2).

Orbital magnetic resonance imaging (MRI) with T1- and T2-weighted sequences identified a 2.2-cm expansile cyst in the left posterior ethmoid sinus, characterized by high signal intensity on T1-weighted images and low signal intensity on T2-weighted images. These findings indicated significant compression of the medial rectus muscle, inferior rectus muscle, and intracanalicular portion of the optic nerve (Fig. 3). Computed tomography (CT) of the facial bones further confirmed a well-demarcated cystic lesion with a density similar to that of brain parenchyma, and revealed diffuse bone erosion involving the anterior ethmoid wall, sphenoid sinus, and orbital apex (Fig. 4).

Consequently, emergency marsupialization of the mucocele was performed via navigation-assisted endoscopic sinus surgery for decompression. The mucoperiosteum-encapsulated mucocele was accessed using a transethmoid approach, and specimens from the drained mucoid discharge were submitted for culture and biopsy (Fig. 5). Bacterial cultures subsequently identified methicillin-resistant Staphylococcus aureus (MRSA). Histopathological analysis revealed degenerated necrotic debris and submucosal granulation tissue with associated inflammation.

Postoperatively, left ocular movement rapidly improved. At the 10-month follow-up, ptosis and external ophthalmoplegia had resolved, and no specific abnormalities were observed in the nasal cavity (Fig. 6). Concurrently, visual acuity improved to 0.4 in the right eye and 0.3 in the left eye.

COVID-19 has been discussed in relation to increased mucus retention within the paranasal sinuses, which may be associated with heightened susceptibility to opportunistic infections. Furthermore, systemic immune dysfunction in patients with COVID-19, together with the widespread use of antibiotics and steroids during the pandemic, has been associated with an increased risk of multidrug-resistant bacterial and fungal infections [3–7]. In this context, antibiotic overuse appears less relevant in the present case, and the findings instead suggest proliferation of pre-existing MRSA colonization within the nasal cavity or mucocele, potentially promoted by high-dose steroid therapy administered for presumed optic neuritis [10]. While mucoceles typically develop over a prolonged period (approximately 11–49 years), secondary infection resulting in pyocele formation can lead to rapid symptom manifestation due to accelerated bone destruction [11,12]. As a mucocele expands and exerts pressure on the surrounding orbital bone, intraorbital compression may occur, resulting in ophthalmic symptoms. Although mucoceles most commonly occur in the frontal and anterior ethmoid sinuses, involvement of the posterior ethmoid or sphenoid sinuses, as observed in this case, may present with symptoms such as visual impairment, diplopia, and headache.

Diagnosis of mucoceles is typically established through a combination of clinical symptoms and imaging studies, with CT serving as a primary diagnostic modality [13,14]. More recently, MRI has become instrumental in evaluating involvement of the optic nerve and other critical structures. T1- and T2-weighted MRI images may demonstrate variable signal intensity patterns depending on the protein concentration of the mucoid cyst contents. However, in cases associated with severe fibrotic changes or fungal infection, low signal intensity may be observed on both T1- and T2-weighted images [15]. Histologically, mucoceles are often encapsulated by mucoperiosteum, as was observed in the present case [12]. Given that biopsy results may occasionally reveal malignancy, histopathological examination of tissues obtained during surgery remains essential [16].

Endoscopic marsupialization has emerged as a key surgical approach for expanding the drainage pathway while preserving normal mucosa, allowing the cyst wall to function as the medial orbital wall. This technique effectively maintains anatomical integrity while reducing postoperative complications and enabling continuous postoperative observation. In cases of mucoceles accompanied by ophthalmic symptoms, rapid surgical decompression plays a critical role in symptom resolution and overall prognosis [17,18]. During the period in which this case occurred, COVID-19 isolation measures were mandatory, and hospital visits were restricted, in contrast to the pre-pandemic era. Ophthalmic symptoms similar to those observed in this patient, although infrequently reported, have been associated with immune-mediated responses following COVID-19 infection, such as post-COVID-19 optic neuritis, or following vaccination. Given the variability in symptom onset timing, a comprehensive differential diagnosis that includes neurological and autoimmune diseases is essential [8,9,19,20].

The rarity of rapid symptom onset in mucoceles, together with the ophthalmic manifestations observed in this patient, underscores the importance of considering mucoceles secondary to infection or other sinus pathologies. Such consideration should be informed by recent COVID-19 infection history, treatment exposure, and vaccination status. Additionally, this case highlights the need for timely surgical intervention in improving ophthalmic outcomes and facilitating accurate differential diagnosis. In cases in which mucoceles with ophthalmic symptoms develop after COVID-19 infection or vaccination, judicious selection of antibiotics and steroids is essential to minimize secondary infections and optimize prognosis.