**Core Concept:** Sinusitis is an inflammation of the paranasal sinuses, usually caused by bacterial or viral infections, although allergic fungal sinusitis and autoimmune diseases can also lead to sinus inflammation. Antibiotics and antihistamines are not effective in treating these conditions and may worsen the condition.

**Why the Correct Answer is Right:** In this case, the patient's symptoms, duration, and inadequate response to antibiotics and antihistamines suggest a fungal sinus infection (allergic fungal sinusitis). The CT scan shows mucopurulent discharge from the middle meatus and inflamed sinus openings, which are typical findings in such cases.

**Why Each Wrong Option is Incorrect:**

A. Antibiotics: Inadequate response to antibiotics (mentioned in the question) and the likely fungal nature of the infection rule out antibiotics as a treatment option.
B. Anti-histamines: Similar to antibiotics, inadequate response to antihistamines further suggests a fungal sinus infection rather than allergic rhinitis or nasal allergy.
C. Antibiotics and antihistamines together: Combined use of antibiotics and antihistamines does not address the root cause of the infection and may worsen the condition, leading to incorrect diagnosis and treatment.
D. Antibiotics and antihistamines together: Similar to option C, the use of both antibiotics and antihistamines is inappropriate for a fungal sinus infection.

**Clinical Pearl:** Allergic fungal sinusitis is a distinct entity that can present with similar symptoms as rhinosinusitis and requires appropriate management. Misdiagnosis can lead to unnecessary use of antibiotics and antihistamines, worsening the condition. A thorough clinical examination, including nasal endoscopy, and imaging studies, such as CT scan, are essential for accurate diagnosis.

**Correct Answer:** **C. Antibiotics and antihistamines together**

**Why Each Wrong Option is Incorrect:**

A. Antibiotics: As mentioned earlier, antibiotics are not effective in treating fungal sinus infections.
B. Anti-histamines: Similar to antibiotics, antihistamines are not indicated for treating allergic fungal sinusitis and may worsen symptoms.
C. Antibiotics and antihistamines together: Combining antibiotics and antihistamines addresses the root cause of the infection and provides symptomatic relief, making it the correct answer.