Delayed diagnosis of central skull-base osteomyelitis with abscess: case report and learning points

Abstract

Central skull-base osteomyelitis (CSBO) is a rare life-threatening infection, usually resulting from medial spread of necrotising otitis externa. Here, we describe a case with no identifiable source of infection, causing a delay in diagnosis. An 80-year-old man with Crohn's disease treated with mesalazine presented with collapse and tonic-clonic seizure. Computed tomography and magnetic resonance imaging showed a nasopharyngeal mass that was initially thought to be a neoplasm. Awaiting formal biopsy, he represented with collapse and repeat imaging showed features of abscess formation. Review of previous scans revealed skull-base erosion and the diagnosis was revised to skull-base osteomyelitis. This is the first reported case of CSBO associated with mesalazine use, an aminosalicylate used in Crohn's disease. It is only the second reported case with abscess formation. We discuss the learning points in making a timely diagnosis and examine the potential association of factors such as mesalazine use and abscess formation in this case.

Keywords: Abscess; Crohn’s disease; Mesalazine; Osteomyelitis; Skull base.

Figure 1A

Axial computed tomography showing subtle clival erosion on the right side (arrow) which was not appreciated at the time of the examination

Figure 1B

Axial T2 magnetic resonance imaging showing the inferior slices of the study and demonstrating a T2 hyperintense retropharyngeal/preclival mass (asterisk); bilateral middle ear and mastoid effusions are also present

Figure 2A

Sagittal T1 magnetic resonance imaging showing loss of the normal T1 fat signal in the clivus (arrow); the preclival mass is again noted (arrowhead)

Figure 2B

Fat-saturated axial T1 post IV gadolinium scan demonstrating a rim-enhancing mass in the preclival region consistent with an abscess (arrowheads); diffuse inflammatory change and enhancement is seen in the clivus and surrounding soft tissues, in keeping with central skull base osteomyelitis; note the abnormal retroclival dural enhancement (arrows)

Figure 3

An axial computed tomography guided biopsy was performed using a paramaxillary and subzygomatic approach

Figure 4

Fat-saturation axial T1 post IV gadolinium post-treatment scan showing a marked reduction in size of the preclival abscess with a residual rim-enhancing cleft seen on the right side (arrow); the clivus signal has now returned to normal and the dural enhancement has also resolved