Imaging of mucormycosis skull base osteomyelitis

Abstract

Skull base osteomyelitis (SBO) is typically bacterial in origin and caused by Pseudomonas, although the fungus Aspergillus has also rarely been implicated. SBO generally arises from ear infections and infrequently complicates sinonasal infection. Rhinocerebral Mucor infection is characteristically an acute, fulminant, and deadly infection also affecting the orbits and deep face and is associated with intracranial complications. Bony involvement is uncommon because of the angioinvasive nature of the fungus. More recently, chronic invasive Mucor sinusitis has been described. We report the unusual clinical and imaging features of a patient with biopsy-proven invasive mucormycosis arising from chronic isolated sphenoid sinus disease, who presented with extensive SBO and a paucity of deep facial, orbital, or intracranial involvement.

fig 1.

Axial CT image through the skull base. A 5-mm-section using a standard soft-tissue algorithm and bone windowing shows mucosal thickening in the sphenoid sinuses, focal bony destruction of the right lateral sphenoid sinus wall (white arrowheads), and subtle lytic foci in the clivus (black arrowheads). fig 2.  Photomicrograph of the sphenoid sinus wall reveals broad hollow-appearing hyphae with 90° branching (arrowheads at 90° to each other) characteristic of mucormycosis. A large necrotic bone fragment is seen centrally (methanamine silver stain, original magnification ×400)

fig 3.

MR images through the skull base. A, Axial T1-weighted (600/12/2 [TR/TE/excitations]) MR image, obtained from an outside institution and performed 10 weeks prior to CN VI palsy onset, reveals foci of signal hypointensity in the clivus and bilateral petrous apexes (arrowheads). B, Axial T1-weighted (600/9/2) MR image, obtained at our institution 10 weeks after A, shows progressive heterogeneity of the marrow fat in the central skull base. C, Contrast enhanced fat-suppressed coronal T1-weighted (600/9/2) MR image shows bilateral, thick, smooth enhancement of the dura of the medial wall and floor of the middle cranial fossae (arrowheads) and abnormal marrow enhancement in the clivus (asterisk). fig 4.  A 3-mm-thick CT image obtained using a high-resolution bone algorithm postoperatively more clearly shows the extensive erosive changes in the central skull base (brackets)