Presentation
Headaches and photophobia with intermittent nausea and vomiting for several years. Physical, neurological and laboratory investigations were unremarkable.
Patient Data
CT scan of the skull base demonstrates a lesion with sclerotic borders and internal curvilinear calcifications located in the left sphenoid bone, anterior clinoid process and petrosal apex. Normal position and aspect of the vidian canals and inferior orbital fissures, indicating no mass effect.
The lesion in the apex of the left petrosal and sphenoid bone, without evidence of a mass effect, demonstrates heterogeneous high signal in T1 and T2 acquisitions. T1 fat saturation with post gadolinium acquisition demonstrates low signal. These features suggest fat and cystic components.
Case Discussion
The normal process of pneumatization of the skull base and paranasal sinuses starts at the age of 4 months and develops through young adulthood. Redbone marrow is being replaced by fatty marrow prior to pneumatization of the paranasal sinuses, including the sphenoid bone. The precise mechanisms that remain largely unclear. This bone marrow conversion precedes the invasion of epithelial cells to form the respiratory mucosa. When one of the steps described above is halted, no or reduced pneumatization of the sinus will occur.
Imaging consists of CT and MR studies involving the skull base.
CT findings: characteristic features on CT is the presence of
- a non-expansile lesion with
- internal curvilinear calcifications and
- sclerotic margins
MRI findings: the hallmark of MR imaging is
- presence of internal fat and microcystic components
- absence of any mass effect
The non-expansile nature of the lesion is best evaluated at the inferior orbital fissure and vidian canal, which are not displaced nor disrupted.
Differential Diagnosis:
In contrast with arrested pneumatization, all of these conditions lack the presence of internal fat or usually show signs of mass effect on the surrounding structures.
With courtesy of Drs. M. de Jong and Drs. Th. Fassaert
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