*28 year-old male with headache.
What is the most likely diagnosis?
1. Pneumocephalus
2. Abscess
3. Multiple myeloma
4. Dermoid cyst rupture
Answer
Answer: Pneumocephalus secondary to trauma
Case Discussion:
Scout image demonstrates multiple round lusen lesions mimicking multiple myeloma.
Axial CT images show displaced nasal bone fracture and extensive pneumocephalus throughout the intracranial extraaxial compartment.
Pneumocephalus is the presence of intracranial gas, and the gas is generally air. Trauma and surgery is the most common cause (1).
Pneumocephalus can be divided into two groups according to their location;
Extra-axial (epidural, subdural, subarachnoid)
Intra-axial (parenchymal, intra-ventricular, intra-vascular)
The underlying cause: mechanical trauma (common), instrumentation (neurosurgery, sinus surgery, etc.), barotrauma, otogenic pneumocaphalus, pneumosinus dilatans, meningitis from a gas forming organism (rare) (1, 2, 3)
On CT, air has a very low density (near -1024HU). Fat mimics this appearance but it has a higher density than air (near -90HU).
References:
1. Zasler ND, Katz DI, Zafonte RD. Brain Injury Medicine, Principles And Practice. Demos Medical Publishing. (2007) ISBN:1888799935.
2. Alviedo JN, Sood BG, Aranda JV et-al. Diffuse pneumocephalus in neonatal Citrobacter meningitis. Pediatrics. 2006;118 (5): e1576-9. doi:10.1542/peds.2006-1224
3. Jensen MB, Adams HP. Pneumocephalus after air travel. Neurology. 2004;63 (2): 400-1.