How a Sinus Infection Is Diagnosed

The diagnosis of a sinus infection (sinusitis) is usually based on your symptoms and a physical exam. If symptoms continue and aren't resolved with treatment, X-rays or a CT scan may be performed. Sometimes direct sinus visualization with a tiny fiber-optic endoscope will be done and a specimen may be taken for microscopic exam and culture. Though not all sinus infections require treatment, identifying one early—and starting medication, if necessary—can not only help you feel better sooner but potentially prevent the infection from progressing.

sinusitis diagnosis
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Self-Checks

Most sinus infections are caused by a viral infection such as the common cold. Because your doctor will want to avoid giving you antibiotics unnecessarily (they only work for bacterial sinusitis, not viral), it's typically advised that you wait and see if your symptoms get better over the course of a few days before treatment is considered.

While you wait, take note of when your symptoms began and how they have progressed. This information will be helpful to your doctor if you end up seeking an evaluation.

Whether in infants, children, or adults, a cold should get better after a week. The virus can involve the sinuses and produce nasal congestion, sinus pressure, and mucus drainage for as long as 10 days. At that point, a viral sinus infection should show improvement.

However, if it has been 10 days and the symptoms are not getting better—or they improved, but then worsened (what's called double sickening)—a bacterial sinus infection may have developed. Other signs include a persistent or high fever; severe sinus pain, especially on only one side; and discolored nasal discharge, especially on just one side. These should prompt you to call your doctor to get an appointment for an examination and diagnosis.

If at any time you experience severe symptoms, including changes in your vision, swelling around the eyes or forehead, severe headache, or confusion, you should see your doctor immediately. These are serious signs that a bacterial sinus infection is spreading.

Examination

Sinus infections can be diagnosed and treated by your pediatrician or primary care provider. Typically, sinus infections are diagnosed solely on a patient's symptoms and a medical examination.

Be sure to share all of the information you've taken note of: when your sinus infection started, what symptoms you've been experiencing, and, if you've had previous infections, when they occurred and how long they took to resolve. Having four or more sinus infections in a year will lead your doctor to look for contributing factors that are increasing your risk. Share any known risk factors, including a history of allergies, asthma, and any conditions that could weaken your immune system.

The physical exam itself will likely include checking inside your nose with a speculum and flashlight. Your doctor will note where you feel pain or tenderness as this can point to which of the sinuses is involved. Your doctor will also look for purulent drainage in the nose and throat. Looking in the nose can help determine if there is a foreign body, deviated septum, nasal polyps, tumor, or nosebleed.

Labs and Tests

Your doctor may choose to run some tests, but this is not done in every case. These may include:

  • A culture of nasal drainage collected via a swab of the nose or sinus
  • Blood tests (erythrocyte sedimentation rate, CBC, C-reactive protein)
  • Allergy testing, especially for a chronic sinus infection or repeat sinus infections

Imaging and Procedures

Imaging usually isn't done in cases of acute sinusitis. It is mostly used for chronic sinusitis or recurrent sinusitis to look for structural causes. It may also be performed if you have severe acute symptoms that hint that the infection might be spreading. 

An X-ray sinus series can be performed to detect fluid in the sinuses and nasal polyps. A CT scan gives a more thorough view of the sinuses and it is now preferred. MRIs are less commonly used because they don't distinguish air from the bone.

In some cases, a doctor will perform a rhinoscopy (nasal endoscopy) to look into the nasal passages. You may be referred to an ENT specialist for this procedure. The nasal endoscope is a thin tube that is inserted into your nose to see your nasal passages and sinuses. It contains a light, fiberoptic cable, and a lens for viewing. It may be attached to a video camera so the doctor can see the images on a screen and record the exam.

To make you more comfortable during rhinoscopy, you'll be given a nasal decongestant spray and a local anesthetic spray to numb the nose. This exam can be used to check for nasal polyps, a deviated septum, enlarged turbinates, tumors, and pus. It can also be used to remove tissue so your doctor can check for bacterial or fungal infection.

Your doctor may want to positively identify the organism responsible for the sinus infection, especially in cases of an infection that doesn't respond to antibiotics or is spreading. This sample is obtained through nasal endoscopy or sinus puncture in order to avoid contamination with bacteria found in the nasal passages. A sinus puncture is done by numbing the puncture site (usually just below the nose or inside the mouth), inserting a needle, and withdrawing an aspirate.

Differential Diagnoses

Your doctor will first want to differentiate between allergic, viral, bacterial, or fungal causes of the symptoms of the sinus infection. Allergic rhinitis typically has clear nasal drainage rather than the thick, yellow or green drainage seen in bacterial or fungal sinusitis. The doctor may refer you for allergy testing if this is suspected. If you primarily have facial pain and a headache, the source could be a migraine rather than sinusitis. There are also cases, especially in children, of a foreign body stuck up the nose that is causing the inflammation.

The waiting period before treating with antibiotics helps the doctor ensure she isn't overprescribing antibiotics, which will not help resolve viral sinusitis, allergic rhinitis, or other non-infectious inflammatory reactions, and can lead to resistance. 

If the symptoms persist for more than 10 days and the examination shows signs of sinus involvement, or if you have a fever, the doctor may prescribe antibiotics on the presumption that it is acute bacterial sinusitis.

Acute sinusitis will clear up by four weeks. Once you have had the symptoms for 12 weeks it will be called chronic sinusitis. This can be due to causes including allergies, allergic fungal sinusitis, fungal sinusitis, nasal polyps, benign or malignant sinonasal tumors, enlarged turbinates, or a deviated septum.

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Article Sources
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  • Radojicic C. Sinusitis. Cleveland Clinic. http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/allergy/rhino-sinusitis/.
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