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Arrested pneumatisation of the sphenoid

Case contributed by: Dr Erik Ranschaert

Presentation:

this 24 year-old woman was complaining of headaches and photophobia with intermittent nausea and vomiting for several years. Physical, neurological and laboratory investigations were unremarkable

From the case: Arrested pneumatisation of the sphenoid
Modality: CT

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  • <p>CT skull base</p> Axial CT scan of the skull base shows a lesion with sclerotic borders and internal curvilinear calcifications located in sphenoid bone, anterior clinoid process and petrosal apex. There is a normal position and aspect of the vidian canal and inferior orbital fissure, indicating no mass effect

non-contrast

CT skull base

Axial CT scan of the skull base shows a lesion with sclerotic borders and internal curvilinear calcifications located in sphenoid bone, anterior clinoid process and petrosal apex. There is a normal position and aspect of the vidian canal and inferior orbital fissure, indicating no mass effect
From the case: Arrested pneumatisation of the sphenoid
Modality: MRI

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  • <p>MRI axial + gadolinium</p> Plain axial T1-weighted imaging shows a heterogeneous high signal localized in the apex of the left petrosal and sphenoid bone without evidence of mass effect. In these series with Gd-DOTA and fatsat the lesion shows low signal without enhancement indicating fatty content

T1 C+ fat sat

MRI axial + gadolinium

Plain axial T1-weighted imaging shows a heterogeneous high signal localized in the apex of the left petrosal and sphenoid bone without evidence of mass effect. In these series with Gd-DOTA and fatsat the lesion shows low signal without enhancement indicating fatty content

Case Discussion:

The normal process of pneumatisation of the skull base and paranasal sinuses starts at the age of 4 months and develops through young adulthood. Red bone marrow is being replaced by fatty marrow prior to pneumatisation 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 pneumatisation 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: 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 cannal, which are not displaced nor disrupted.

Differential Diagnosis: 

  • fibrous dysplasia
  • ossifying fibroma
  • chondrosarcoma
  • osteomyelitis
  • chordoma 
  • bone metastasis

In contrast with arrested pneumatisation, 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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