Differential Diagnosis

The patient's presentation of left eye swelling, left frontal headache, and progressive left ptosis, along with the laboratory and imaging findings, suggests an invasive fungal infection. The key findings include:

• Elevated WBC count with neutrophilia
• Elevated blood glucose indicating diabetes mellitus
• CT scan showing fluid in both ethmoid sinuses and inflammatory changes lateral to the left medial rectus muscle
• KOH preparation demonstrating broad, aseptate hyphae

Single Most Likely Diagnosis

• Mucorales (Mucormycosis): This is the most likely diagnosis given the patient's diabetic status, the presence of broad, aseptate hyphae on KOH preparation, and the clinical presentation of invasive fungal sinusitis with orbital involvement.

Other Likely Diagnoses

• Aspergillus: While Aspergillus species typically show septate hyphae, some species can appear aseptate, and this diagnosis should be considered, especially in an immunocompromised patient. However, the broad, aseptate hyphae are more characteristic of Mucorales.
• Fusarium: This fungus can also cause invasive sinusitis and has a variety of clinical presentations. However, it is less commonly associated with the specific findings in this case compared to Mucorales.

Do Not Miss Diagnoses

• Invasive Aspergillosis: Although less likely given the aseptate hyphae, invasive aspergillosis can present similarly and is critical to diagnose due to its high mortality rate if left untreated.
• Bacterial Sinusitis/Orbital Cellulitis: While the fungal elements are a key finding, bacterial infections can coexist or mimic fungal infections, and missing a bacterial cause could lead to inadequate treatment.

Rare Diagnoses

• Entomophthorales (Entomophthoromycosis): This is a rare cause of fungal infection that can present with similar clinical findings but is less common and typically associated with a more subacute presentation.
• Other Rare Fungal Pathogens: Various other fungi can cause invasive sinusitis, but they are less common and would be considered based on specific risk factors or exposures not mentioned in the case presentation.