Diagnosis suspicion
Diagnosis of MEO is suspected in patients suffering from persistent otorreha and otalgia
Sometimes Cranial nerve palsy : essentially homolateral facial nerve palsy .
MEO is a challenging disorder to diagnose and imaging should be performed as soon as diagnosis is suspected.
(CT) being as an easy and fast method to acquire to overview of the Temporal bone ,is the
most commonly used imaging modality for diagnosis and follow-up of MEO.
CT protocol :
The examination consists of acquisition in the axial with high resolution reconstruction in coronal and sagittal planes interesting Skull base to the sus claviculair plane before and after biphasic (pre impregnation) contrast injection.
CT has a main role in evaluation of bone erosion especially with the use of (ultra)thin high-resolution.
MRI with its better resolution and higher soft tissue detail may be of better apport in evaluating the spread of infection in soft tissues , and bone marrow.
MRI protocol :
The standard protocole includes 4 sequences in two planes : axial and coronal :
T1-Weighted Sequences without Fat supression in order to evaluate extension de skull base bone :Loss of high signal of bone marrow , stranding fat in deep spaces of head and neck.
T2-Weighted Sequences also to evaluate inflammation extension to soft tissues.
T1 Weighted Sequences + Fat saturation and gadolinium injection : Involved skull base osseous structures and soft tissues will enhance diffusely .
Diffusion-Weighted Imaging used as an additionnel sequence aiding in the differentiation
between lymphoma/nasopharynx carcinoma and bacterial infection.
Additionnal sequences : T1 weighted sequence with Fat saturation , T2 with Fat saturation , STIR
Findings and procedure details :
Our study was retrospective including 15 patients with MEO hospitalized at Rabta hospital.
CT with contrast was performed for all our patients for diagnosis .
MRI with contrast materiel was performed in only 5 patients before instauring treatment.
MEO starts in the external auditory canal in the bony-cartilaginous junction.
It spreads along the temporal bone through the fissures of Santorini extending to surrounding soft tissues and bone .
Kwon et al. described four spreading patterns of the soft tissue extension :
1/Anterior spreading : involves extension to Temporo –mandibular joint leading to arthritis ( condilar bone erosion erosion and bone marrow infiltration ) , to masticator space ( thickening of muscles and contrast enhancement), also parotid gland is envolved and facial nerve.
2/ Posterior spreading : to the mastoid causing mastoiditis , the peri mastoid soft
tissues and the stylo mastoid foramen causing infiltration and enhancement of facial nerf
3/ In medial pattern : there is extension to the petrous bone apex , sphenoid , clivus and jugular foramen associated to bone erosion .
There is ipsilateral parapharyngeal fat infiltration with nasopharyngeal wall thickening and/or ipsilateral preclival soft tissue infiltration, cranial nerves IX ,X, XI involvement( stranding fat in jugular foramen associated to perinervous enhancement)
4/Superiorly : Dural enhancement with intra cranial extension through skull base foramina.
Some complications may be noted as :
Intra cranial extension and Abscesses in the epidural space, brain parenchyma
Spreading to the prevertebral space with abcess , and dural involvement
Venous sinus thrombosis.
Cranial nerve involvement
On CT soft-tissue thickening and bone erosion in the external auditory canal were noted in all patients ( Figure 1)
All examinations showed stranding fat in homolateral parapharyngeal space .
Extension to mastoid and stylo-mastoidien foramen were noted in 5 patients.
Bone erosion of the temporo-mandibular joint associated to arthritis in 4 cases.
Retropharyngeal abcess was noted in one patient also associated to jugular and sigmoid sinus thrombosis .(Fig
Intra cranial extension was noted in 3 patients with dural enhancement and cranial nerve involvement.
CT and MRI for follow up where performed in only 3patients .
At present, there is no consensus about the preferred imaging method of SBO follow-up.
There is no followed protocol for follow up . It depends in clinical and biological evolution.
Follow-up via CT scan is not a good reliable tool as measuring recovery by bone remineralization, however, this does not immediately occur after disease resolution. It may show regression of soft tissue infiltration also .
MRI imaging is known To be a reliable Imaging modality to monitor soft tissue changes , however , an abnormal bone marrow caan still 6-12 months after recovery .