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                Spontaneous lateral sphenoid cerebrospinal fluid fistula: MRI diagnosis

                Matthew Goodier, MB ChB
            

            Darlene Lubbe, 

            Savvas Andronikou, MB BCh, FCRad, FRCR (Lond), PhD
        

        Rene Truter, MB ChB, MMed (Radiol)
    

    Department of Radiology, University of the Witwatersrand, Johannesburg

    
        Corresponding author: M Goodier (goodiermatt@gmail.com)

        
            Abstract

            Spontaneous
            or primary cerebrospinal fluid (CSF) fistula is a rare cause of CSF
            rhinorrhoea. Magnetic resonance imaging with high-resolution highly
            T2-weighted images is valuable in pre-operative localisation and
            characterisation of the defect, particularly if a transnasal endoscopic
            approach is planned. This report describes the radiological evaluation
            and surgical management of a 53-year-old man who presented with a
            spontaneous lateral sphenoid CSF fistula.

        

        
        

        Case report

        We present the case of a 53-year-old man who
        presented with a primary complaint of a lateral tongue tumour. During
        admission for surgery, a large lesion was noticed on his occiput. An
        MRI revealed a large occipital meningioma for which he had a subtotal
        resection. Postoperatively he presented with an unexplained spontaneous
        CSF leak through the right sphenoid sinus. The patient never had
        documented raised pressures, and it was felt that the remaining tumour
        residue could not be responsible for causing raised intracranial
        pressure.

        The MRI performed at the time demonstrated a
        herniation of meninges through a bony defect in the lateral wall of the
        right sphenoid sinus and subtle features of encephalomalacia of the
        adjacent temporal lobe (Figs 1a - c).

        An endoscopic transsphenoidal reduction of the meningocoele and obliteration of the right sphenoid sinus was performed.

        At surgery, a 1x1 cm dehiscent area in the right
        sphenoid sinus was present. There was some mucosal thickening with
        visible dura which was cauterised to identify the actual leak. The
        sinus was cleared of all mucosa and obliterated with fat. Six weeks
        post-operatively, the patient was well, with no further CSF leak.

        Discussion

        The presence of CSF rhinorrhoea indicates the
        existence of an abnormal communication between the intracranial CSF
        spaces and the nasal cavity (or via the eustachian tube from a temporal
        bone fracture and CSF-leak). Post-traumatic CSF rhinorrhoea as a
        complication of a base of skull fracture is the most common cause.
        Non-traumatic causes of CSF rhinorrhoea make up only 3 - 4% of cases1 
        and comprise several causes such as skull base tumours, destructive
        granulomatous processes such as Wegener’s granulomatosis, and
        complicated sinonasal infections.1
    

    Spontaneous, or primary, CSF fistula is a
    separate entity with no underlying cause of the CSF leak. Spontaneous
    leaks are more common in obese middle-aged women, and there is commonly
    a co-existing encephalocele of variable size.2 
    The pathogenesis of this condition is thought to be due to a
    combination of embryological and acquired factors. The medial aspect of
    the temporal bone may fail to develop, resulting in a persistent
    lateral craniopharyngeal canal (also known as the Sternberg canal)
    between the middle cranial fossa and the pneumatised inferolateral
    recess of the sphenoid sinus.3  Idiopathic intracranial hypertension (pseudotumour cerebri) and empty sella syndrome are also known to occur in these patients,2 
    suggesting that chronically increased intracranial pressure with
    localised thinning of the bone may also play a role in the pathogenesis
    of this condition.4


Spontaneous CSF fistulae are most common in
the anterior cranial fossa, at the ethmoid roof and cribriform plate.
Less common sites include the sphenoid sinus, around the sella or at
the inferolateral or pterygoid recesses.2


The goals of imaging in CSF fistulae are to confirm
the diagnosis, evaluate any underlying cause, localise the defect site
and exclude an associated meningoencephalocoele at the defect.2 
Successful treatment depends on the accurate pre-operative localisation
of the site of the fistula. This is especially true as most defects are
now repaired by means of endoscopic surgery. An open approach via a
craniotomy may be required in large defects or in well pneumatised
sphenoid sinuses where the defect is located in the lateral recess of
the sphenoid sinus. Pure obliteration of the sphenoid sinus would
rarely be successful in large defects, and a vascularised flap is often
needed in these instances. The mucoperichondrial septal flap, pedicled
on the posterior septal artery, is a useful flap when endoscopic repair
is considered.

High-resolution CT scanning alone has a low
sensitivity for the detection of the osseous-dural defect. Accuracy may
be increased by introducing low-oslomar contrast materal into the
subarachnoid space (CT cisternography), which improves the sensitivity
for active leaks to 80 - 85%.3 
Inactive or intermittent fistulae may not be demonstrated, however. CT
is best for bony anatomical detail and is useful in pre-operative
planning.

Magnetic resonance imaging (MRI) provides
complementary information and appears to have a higher sensitivity than
CT scanning, with accuracy rates for detection of the site of even
inactive fistulae as high as 100%.5 
High-resolution highly T2-weighted images such as are obtained by the
constructive interference in the steady state (CISS) sequence are the
most useful. MRI is also able to depict the contents of any associated
encephalocoele. Subtle encephalomalacia as seen in our patient is often
present at the site of the leak.2  MRI was sufficient to allow accurate pre-operative assessment in our patient.

Surgery for spontaneous CSF leaks has traditionally been performed transcranially. Success rates of up to 80%2 
have been reported; however, there is additional morbidity related to
the craniotomy as well as the risk of anosmia owing to damage to the
olfactory tracts.

Transnasal endoscopic surgical techniques are now increasingly performed, especially for small defects.6  In experienced hands, the reported success rates approach 90%, which is superior to open repair.2 
Some cases, however, are not amenable to endoscopic techniques; these
include high-pressure leaks, patients with multiple defects, large
defects or very well pneumatised sphenoid sinuses with lateral recesses.2


Conclusion

Spontaneous or primary CSF fistula is a rare cause
of CSF rhinorrhoea. Various imaging modalities including CT, CT
cisternography, MRI and radio-isotope scanning may be used for
preoperative evaluation. MRI with high-resolution and highly
T2-weighted images are most valuable in preoperative localisation and
characterisation of the defect, especially if a transnasal endoscopic
approach is planned.




1. Pandey AK. Case report: Anteromedial temporosphenoidal encephalocele
with a clinically silent lateral bony defect in the greater wing of the
sphenoid. Indian J Radiol Imaging 2009;19:311-313.

1. Pandey AK. Case report: Anteromedial temporosphenoidal encephalocele
with a clinically silent lateral bony defect in the greater wing of the
sphenoid. Indian J Radiol Imaging 2009;19:311-313.

2.	Lloyd KM, DelGaudio JM, Hudgins PA. Imaging of skull base cerebrospinal fluid leaks in adults. Radiology 2008;248:725-736.

2.	Lloyd KM, DelGaudio JM, Hudgins PA. Imaging of skull base cerebrospinal fluid leaks in adults. Radiology 2008;248:725-736.

3.	Wind JJ, Caputy AJ, Roberti F. Spontaneous encephaloceles of the temporal lobe. Neurosurg Focus 2008;25:1-6.

3.	Wind JJ, Caputy AJ, Roberti F. Spontaneous encephaloceles of the temporal lobe. Neurosurg Focus 2008;25:1-6.

4. Schuknecht B, Simmen D, Briner HR, Holzmann D. Nontraumatic skull
base defects with spontaneous CSF rhinorrhea and arachnoid herniation:
imaging findings and correlation with endoscopic sinus surgery in 27
patients. Am J Neuroradiol 2008;29:542-549.

4. Schuknecht B, Simmen D, Briner HR, Holzmann D. Nontraumatic skull
base defects with spontaneous CSF rhinorrhea and arachnoid herniation:
imaging findings and correlation with endoscopic sinus surgery in 27
patients. Am J Neuroradiol 2008;29:542-549.

5. Johnson DB, Brennan P, Toland J, O’Dwyer AJ. Magnetic
resonance imaging in the evaluation of cerebrospinal fluid fistulae.
Clin Radiol 1996;51:837-841.

5. Johnson DB, Brennan P, Toland J, O’Dwyer AJ. Magnetic
resonance imaging in the evaluation of cerebrospinal fluid fistulae.
Clin Radiol 1996;51:837-841.

6. Arai A, Mizukawa K, Nishihara M, Fujita A, Hosoda K, Kohmura E.
Spontaneous cerebrospinal fluid rhinorrhea associated with a far
lateral temporal encephalocele – case report. Neurol Med Chir
(Tokyo) 2010;50:243-245.

6. Arai A, Mizukawa K, Nishihara M, Fujita A, Hosoda K, Kohmura E.
Spontaneous cerebrospinal fluid rhinorrhea associated with a far
lateral temporal encephalocele – case report. Neurol Med Chir
(Tokyo) 2010;50:243-245.




    
        
    

    
        Figs 1a - 1c. MRI scans of the brain and sphenoid
        sinus in a patient with lateral sphenoidal CSF fistula. (1a) Coronal
        (1b)sagittal and (1c) high-resolution axial T2-weighted images
        demonstrate a herniation of CSF-filled meninges from the right middle
        temporal fossa into the right sphenoid sinus through a bony defect
        (arrow). There is subtle encephalomalacia of the right temporal pole.