Cranial CSF fistula

General

Aka: CSF leak.

Types

Traumatic

Iatrogenic (post op)

Transphenoidal
Mastoid surgery
Transmastoid approaches for vestibular schwannoma
FAKE CSF leak: Skull-base surgery (especially involving greater superficial petrosal nerve)

Pseudo-CSF rhinorrhea
Due to nasal hypersecretion from imbalanced autonomic regulation of the nasal mucosa ipsilateral to the surgery.
Presents with

Nasal stuffiness and
Absent ipsilateral lacrimation,
Facial flushing

Post traumatic

67–77% of all CSF leak cases
2–3% of all patients with head injury
8.9% of penetrating trauma has CSF leak

Can be Acute or Delayed

Atraumatic

Aetiology

High pressure

Hydrocephalus
Tumor

Normal pressure

Congenital defects
Bony erosion from infection or necrosis
Focal atrophy (olfactory or sellar)

Associated with

Agenesis of the floor of the

Anterior fossa (cribriform plate) or
Middle fossa

Empty sella syndrome

Primary
Post-transsphenoidal surgery

Infection of the paranasal sinuses

Tumor

Pituitary adenomas
Meningiomas

Persistent remnant of the craniopharyngeal canal

Congenital anomalies: most involve dehiscence of bone

Dehiscence of the footplate of the stapes (congenital abnormality) which can produce CSF rhinorrhoea via the eustachian tube
Dehiscence below foramen rotundum

Spontaneous posterior fossa CSF fistula

Paediatric

Usually presents with either meningitis or hearing loss

Hearing preserved (Preserved labyrinthine function-hearing and balance)

Present with meningitis.
3 usual routes of fistula

Facial canal: can fistulize into middle ear

Petromastoid canal: along path of arterial supply to mucosa of mastoid air sinuses

Hyrtl’s fissure (AKA tympanomeningeal fissure): links p-fossa to hypotympanum

Between the bony labyrinth and the jugular bulb

Right temporal bone (dry specimen, viewed from be-low). The black arrow and shaded are indicate the jugular fossa and the region where Hyrtl’s fissure emerges. The white arrow indicates the external auditory meatus

Hearing loss (Anomalies of labyrinth)

One of several types of Mondini dysplasias,

Congenital disease one and a half coils of the cochlea instead of the normal two coils
Usually presenting with rounded labyrinth/cochlea that permits CSF to erode through oval or round window into auditory canal

Sac-like cochlea (black arrow)

Amorphous vestibule without any defined semicircular canals (white arrow)

Enlarged vestibular aqueduct (red arrow)

Adult

Presentation

Conductive hearing loss
Serous effusion
Meningitis after an episode of otitis media)
Cerebral abscess.

Occurs most commonly through middle fossa.

May be due to arachnoid granulations eroding into air sinus compartment

Difference between traumatic and atraumatic

Difference	Traumatic	Atraumatic
Pneumocephalus	Common	Uncommon
Anosmia	Common (78%)	Rare
Cessation rate	60% occur within days of trauma, 95% within 3 months	33%
Age	- Adult: child 10:1 - Rare < 2yrs - Child incidence < 1%
Infection rate	50% infected if has penetrating injury + CSF leak

Presentation

Otorrhea or rhinorrhea after head trauma

Recurrent meningitis

Possible routes of egress of CSF

Mastoid air cells (especially after p-fossa surgery, e.g. for vestibular schwannoma (VS))

Sphenoid air cells (especially post-transsphenoidal surgery)

Cribriform plate/ethmoidal roof (floor of frontal fossa)

Frontal sinus air cells

Herniation into empty sella and then into sphenoid air sinus

Along path of internal carotid artery

Rosenmüller’s fossa

Located just inferior to cavernous sinus,

May be exposed by drilling off anterior clinoids to allow access to ophthalmic artery aneurysms

Site of the opening of the transient lateral craniopharyngeal canal

Percutaneously through a surgical or traumatic wound

Petrous ridge or internal auditory canal: following temporal bone fracture or vestibular schwannoma surgery.

Rhinorrhea: through middle ear → eustachian tube → nasopharynx
Otorrhea: via perforated tympanic membrane → external auditory canal

Meningitis in CSF fistula

Incidence with posttraumatic CSF leak: 5–10%

Increases as leak persists > 7 days

Risk higher post neurosurgical procedure vs posttraumatic fistula

Due to elevated ICP common

Meningitis → inflammatory changes at leak site → resultant cessation of the leak

Only temporary (false sense of security)

Pneumococcal meningitis

Is the most common pathogen (83% of cases),
Mortality is lower than in pneumococcal meningitis without underlying fistula (< 10% vs. 50%), possibly because the latter is frequently seen in elderly debilitated patients.
Prognosis in children is worse.

Evaluation

Determining if it is CSF

Examination

Anosmia is present in ≈ 5% of CSF leaks

Characteristics

Clear as water

Fluid does not cause irritation inside or outside the nose

Salty taste

Confirmatory test

Beta-2 transferrin

Present

CSF
Vitreous fluid (eye)

Absent in

Tears
Saliva
Nasal exudate
Serum

Except for newborns and patients with liver disease.

Need to collect 0.5mls

Placed in sterile container and sent with dry ice

Very sensitive and specific

Glucose quantification

Urine glucose detection strips are too sensitive, and may be positive even with excess mucus

Test the fluid shortly after collection to minimize fermentation.

Normal CSF glucose is > 30mg% (usually lower with meningitis), whereas lacrimal secretions and mucus are usually< 5mg%.

A negative test is more helpful since it rules out CSF (except in hypoglycorrhachia (low glucose in the CSF)

45–75% chance of false positive

“Ring sign”

When a CSF leak is suspected but the fluid is blood tinged, allow the fluid to drip onto linen (sheet or pillowcase).

A ring of blood with a larger concentric ring of clear fluid (so-called “double ring” or halo sign) suggests the presence of CSF.

An old, but unreliable, sign

Reservoir sign

A gush of fluid that occurs with first sitting up after a period of recumbency.

Thought to indicate drainage of CSF pooled in the sphenoid sinus.

Not reliable

Radiographic signs

Pneumocephalus on CT or skull X-ray.

20% of patients with CSF leaks

Cisternogram

Intrathecal injection of

Radionuclide tracer followed by scintigram
Radiopaque contrast followed by CT scan

Localizing the site of CSF fistula

90% of the time, localization does not require water-soluble contrast CT cisternography (WS-CTC) (see below).

Detect

Pneumocephalus
Fractures
Skull base defects
Hydrocephalus and obstructive neoplasms. Include thin coronal cuts or reconstructions through anterior fossa all the way back to the sella turcica

Non-contrast (optional): to demonstrate bony anatomy
With IV contrast: leak site has abnormal enhancement of adjacent brain parenchyma

Due to inflammation

Water-soluble contrast CT cisternography (procedure of choice)

Procedure of choice.
Indication

No site identified on plain CT (with coronals)
When patient is leaking clinically (the site is only sometimes identified in the absence of an active leak)
When multiple bony defects are identified, and it is essential to determine which site is actively leaking
If a bony defect seen on plain CT does not have associated changes of abnormal enhancement of adjacent brain parenchyma

Technique

Pre-scan

Use iohexol 6–7ml of 190–220mg/ml injected into lumbar subarachnoid space via 22 gauge spinal needle (or 5ml via C1–2 puncture).
Positioned in -70° Trendelenburg × 3min prone with neck gently flexed

In scan

Prone with head hyperextended with 5mm coronal cuts with 3mm overlap (use 1.5mm cuts if necessary).

May need provocative manoeuvres

Prone (brow up)
In position of leak,
Intrathecal saline infusion (requires Harvard pump)

Positive signs

Accumulation of contrast in air sinuses.

Apparent discontinuity of bone on CT without extravasation of contrast is probably not the site of leakage (bone discontinuities may be mimicked by partial volume averaging on CT).

Plain skull X-ray (helpful in only 21%)

May provide additional information for localization and can
R/O

P-fossa mass
Tumour
Empty sella better than CT
Hydrocephalus.

T2WI fast spin-echo sequences with fat suppression and video image reversal have been used to visualize CSF flow (sensitivity and specificity are 0.87 and 0.57, respectively)

Older tests (abandoned in favour of above)

Radionuclide cisternography (RNC)

Not a contemporary test.
Poor localization.
Some of the studied radiopharmaceuticals are no longer available

Intrathecal (visible) dye studies

Some success with indigo carmine or fluorescein with little or no complications.
❌ methylene blue is neurotoxic and should not be used

Treatment for CSF fistula (initial treatment → CSF drainage → surgical)

Initial treatment

Acutely post trauma, observation is justified as most cases cease spontaneously.

Prophylactic antibiotics

Controversial.

There was no difference in the incidence or morbidity of meningitis between treated and untreated patients.
Furthermore, the risk of selecting resistant strains appears real and is therefore usually avoided.

We do not give unless dirty wound

Pneumococcal vaccine: recommended for adults age 2–65 years

For persistent posttraumatic or post-op leaks Non-surgical treatment

Measures to lower ICP

Bed rest
Avoid straining (stool softeners) and avoid blowing nose
Acetazolamide (250mg PO QID) to reduce CSF production
Modest fluid restriction; caution post-transsphenoidal because of possible DI: 1500ml/day in adults, 75% of maintenance/day in peds

If leak persists (caution: first R/O obstructive hydrocephalus with CT or MRI)

LP: QDS/BD (lower pressure to near atmospheric or until H/A) OR
Continuous lumbar drainage (CLD): via percutaneous catheter.

Two (of many) management options

15 ml/hr
Keep HOB elevated 10–15° and place drip chamber at shoulder level (lower the chamber if leak persists) and leave open to drain (uses pressure to regulate drainage—may be dangerous e.g. if drainage bag falls to floor)

CLD may require ICU monitoring.

If patient deteriorates with drain in place: immediately stop drainage, place patient flat in bed (or slight Trendelenburg), start 100% O₂, get CT or bedside cross-table skull X-ray (to R/O tension pneumocephalus due to drawing in of air)

Surgical treatment

General information

Need to find site of leak preop.

If not

30% develop a recurrent leak post-op,
15% of these developing meningitis before leak is stopped.

Indications

Traumatic CSF leak that persists > 2 weeks in spite of non-surgical measures

Spontaneous leaks and those of delayed onset following trauma or surgery: usually require surgery because of a high incidence of recurrence

Leaks complicated by recurrent meningitis

Leaks through cribriform plate/ethmoidal roof

Extradural approach

ENT preferred choice
If a frontal craniotomy is being performed, an intradural approach should be used since problems may arise in dissecting the dura off of the floor of the frontal fossa, wherein the dura almost always tears and then it is difficult to know if an identified tear is the cause of the leak or if it is iatrogenic.
Fluorescein dye mixed with CSF injected intrathecally may help demonstrate the leak intraoperatively.

CAUTION: must be diluted with CSF to reduce risk of seizures.

Intradural approach

Generally the procedure of choice.
Techniques of intradural approach

If fistula site is unidentified preoperatively, use a bifrontal bone flap.

If the leak is unidentified pre-op and intra-op, then pack both cribriform plates and sphenoid sinus (incise dura over tuberculum sellae, drill through bone to reach sphenoid sinus, remove mucosa or pack it inferiorly, pack with fat).

If fistula site is identified pre-operatively

Close bone defects with fat, muscle, cartilage, or bone.
Close dural defect with fascia lata, temporalis muscle fascia, or pericranium.

Fibrin glue may be used to help hold tissue in place.

Post op

Lumbar drain after craniotomy is controversial.

Some feel CSF pressure may help enhance the seal.
If used, place the drip chamber at the level of shoulder for 3–5 days.

Consider shunt (LP or VP) if elevated ICP or hydrocephalus is demonstrated.

Leaks into sphenoid sinus (including post-transsphenoidal surgery leak)

LP BID or CLD: as long as pressure > 150mmH20 or CSF xanthochromic

If leak persists >3 days: repack sphenoid sinus and pterygoid recesses with fat, muscle, cartilage and/or fascia lata (must reconstruct floor of sella, packing alone is inadequate).

Some recommend against muscle since it putrefies and shrinks.
Continue LP or CLD as above for 3–5 days post-op

If leak persists >5 days: lumboperitoneal shunt (first R/O obstructive hydrocephalus)

More difficult surgical approach: intracranial (intradural) approach to medial aspect of middle cranial fossa

Consider transnasal sellar injection of fibrin glue under local anaesthesia

Petrous bone may present as otorrhea or as rhinorrhea (via the eustachian tube)

Following posterior fossa surgery

See also treatment following vestibular schwannoma surgery

Following mastoid bone fractures

May be approached via extensive mastoidectomy

Due to dehiscence of the footplate of the stapes: may require obliteration of the middle ear and eustachian tube through a tympanomeatal flap