A 68-year-old male with a history of poorly controlled type 2 diabetes mellitus presents to the emergency department with a several-day history of worsening left-sided facial pain, headache, and bloody nasal discharge. He also reports rapidly progressive blurred vision and painful periorbital swelling. On physical examination, he appears acutely ill, with a temperature of 39.1°C, heart rate 110 bpm, and blood pressure 130/80 mmHg. Inspection of the nasal cavity reveals a black eschar on the left nasal septum, and there is noticeable proptosis of the left eye. Laboratory findings are notable for a white blood cell count of 18.5 x 10^9/L and a plasma glucose level of 25.0 mmol/L. What is the most likely diagnosis and the immediate critical next step in management?

A 65-year-old male with a history of uncontrolled type 2 diabetes presents to an outpatient specialty clinic after being referred for persistent, severe headache and worsening facial pain over the past week. He reports nasal congestion that has progressed to a foul-smelling, bloody discharge. His wife notes recent episodes of confusion and decreased responsiveness. On examination, he is found to have unilateral periorbital edema and erythema, with tenderness over the maxillary sinus. A dark, necrotic lesion is visible on the nasal septum. He is febrile. Considering his clinical presentation and underlying comorbidities, what is the most probable diagnosis and the immediate critical intervention required?

A 58-year-old male with a significant history of poorly controlled type 2 diabetes mellitus presents to an urgent care center. He reports a rapidly progressing onset of severe right-sided facial pain, periorbital swelling, and a dark, bloody nasal discharge over the past 72 hours. He also notes blurred vision in his right eye. His wife mentions he has been increasingly lethargic. Vital signs on arrival are: blood pressure 150/90 mmHg, heart rate 105/min, respiratory rate 22/min, and temperature 39.5°C. Physical examination reveals a tender, swollen right periorbital area with proptosis, and a dark, necrotic lesion visible on the right middle turbinate upon rhinoscopy. Cranial nerve examination shows diminished sensation in the V2 distribution on the right. Given this severe and rapidly evolving presentation, what is the most likely diagnosis and the immediate crucial therapeutic intervention?

A 58-year-old male, with a known but poorly managed history of type 2 diabetes mellitus, presents to the emergency department with a 3-day history of progressively worsening headache, severe facial pain, and unilateral periorbital swelling. He also reports blurred vision in the affected eye. On examination, a tender, erythematous swelling is noted around the left orbit, extending to the left side of the nose, with evidence of a dark, necrotic lesion on the nasal septum. His family reports a recent episode of hyperglycemia with altered mental status. Given the rapid progression and alarming physical findings, what is the most likely diagnosis and the immediate critical management strategy?