Skip to content

Computed Tomography (CT) of the Posterior Fossa Without Contrast

Published: August 9, 2026Updated: August 16, 2026

A CT scan uses X-rays to examine the cerebellum, brainstem, and surrounding structures at the back of the brain without IV contrast.

Quick summary

["This scan provides detailed images of the lower back portion of the brain without using injected contrast dye."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
36517-1
Short code
CT Post fossa WO contr
Synonyms
CT Post fossa WO contr
Category
liver
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ct
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What is this test?

A posterior fossa CT scan creates detailed X-ray images of the lower back portion of the brain, including the cerebellum, brainstem, and nearby fluid spaces. This version is performed without injected contrast dye.

Why might I need this test?

This test may be used to evaluate symptoms such as severe headache, dizziness, vomiting, balance problems, weakness, difficulty speaking, or changes in alertness. It can also help assess the brain after head trauma or the spread of a known condition.

How is the test performed?

You will lie on a padded table while a CT scanner rotates around your head and takes X-ray images. The procedure is painless and usually takes only a few minutes, although the scanner may make loud clicking or humming sounds.

How do I prepare for the test?

Usually no fasting or medication changes are needed for a CT scan without contrast. Tell the imaging staff if you are pregnant, may be pregnant, or have recently received imaging material containing contrast; follow any instructions provided by the ordering clinician.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Posterior Fossa CT Without Contrast

Frequently asked questions

Does this CT scan use contrast dye?
No. This test is performed without injected contrast, so you generally do not need to wait before a contrast-enhanced scan.
Is a posterior fossa CT scan painful?
No. The scan itself is painless, but you may feel brief pressure from the table or hear loud scanner noises. Tell the technologist if you are anxious or unable to remain still.
What can the scan show?
It can show structural changes in the cerebellum, brainstem, and surrounding areas, including bleeding, swelling, fluid buildup, tissue loss, or a mass. It cannot determine the cause of every symptom on its own.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy