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CSF Leaks and Sequelae

CSF Leaks

Terminology

CSF anywhere outside the subarachnoid space of the brain and spine is abnormal. CSF leaks are named by location, e.g., CSF rhinorrhea (nasopharynx), CSF otorrhea (temporal bone).

Etiology

CSF leaks can be congenital or acquired. Congenital CSF leaks can occur with a cephalocele, persistent craniopharyngeal canal, or cribriform plate defect.

Acquired CSF leaks can be spontaneous, posttraumatic, or iatrogenic. Spontaneous intracranial CSF leaks are most commonly associated with arachnoid granulations in the

(34-43A) Bone CT in a patient with a spontaneous CSF leak shows a defect in the right sphenoid wing and sphenoid sinus air-fluid level . (34-43B) T2 FS scan in the same patient shows fluid filling the right sphenoid sinus . The left sphenoid is normally aerated. In-111 DTPA cisternogram (not shown) demonstrated activity in nose and sphenoid sinus, confirming CSF leak. (Courtesy H. R. Harnsberger, MD.)

(34-44A) Axial T2WI in a patient with severe headaches and recurrent meningitis shows fluid filling the right mastoidand filling defect in temporal bone . (3444B) Coronal CT cisternogram in the same patient shows contrast in the CPA cistern entering the petrous temporal bone through a defect caused by a giant arachnoid granulation , then filling the mastoidand middle ear . (Courtesy H. R. Harnsberger, MD.)

lateral sphenoid sinus. Posttraumatic CSF leaks typically occur with fractures of the sphenoid sinus, cribriform plate, or ethmoid roof. Iatrogenic CSF leaks are seen with skull base surgery or following functional endoscopic sinus surgery.

Clinical Issues

Epidemiology and Demographics. CSF leaks can occur in patients of all ages. Trauma, prior skull base operation, and sinonasal surgery are common antecedents. Spontaneous CSF leaks usually develop in middle-aged obese women with idiopathic intracranial hypertension.

Presentation. The most common symptoms are CSF rhinorrhea, especially if the nasal discharge increases with Valsalva or head-down maneuvers.

Imaging

CT Findings. Bone CT with multiplanar reformations is the procedure of choice and may obviate the need for invasive CT cisternography. A bone defect, with or without an air-fluid level in the adjacent sinus, is the typical finding (34-43). Defects under 3 or 4 mm may be difficult to detect, especially in areas where the bone is normally very thin.

CT cisternography is indicated if standard bone CT is negative or shows more than one potential leakage site (34-44).

MR Findings. MR is generally used only if CT is negative or the presence of brain parenchyma within a cephalocele is suspected. T2 scans disclose an osseous defect with fluid in the adjacent sinus cavity.

Nuclear Medicine. In isotope cisternography, CSF is labeled with intrathecal Tc-99m or In-111 DTPA, and the activity over the head and spine is scanned. Pledgets can be packed into

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the nose or ear and then counted, usually 1-2 hours after tracer injection. Pledget counts should be at least 1.5 times the serum count.

Differential Diagnosis

The major differential diagnosis of a cranial CSF leak is a skull base defect without CSF leak. Some areas of the skull base—such as the cribriform plate, olfactory recesses, and petrous ridges—are often very thin.

Intracranial Hypotension

Intracranial hypotension is a poorly understood, frequently misdiagnosed entity that can present with a wide variety of symptoms. Imaging is key to the diagnosis, sometimes providing the first insight into the cause of often puzzling symptoms.

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Terminology

Intracranial hypotension is also known as CSF hypovolemia syndrome.

Etiology

Intracranial hypotension can be spontaneous (SIH) or acquired. Common antecedent causes include lumbar puncture, spinal surgery, and trauma. Patients with Marfan and Ehlers-Danlos syndromes have abnormal connective tissue and an increased risk of CSF rupture through the congenitally weakened dura.

Spinal meningeal diverticula can rupture suddenly and may be responsible for many cases of "spontaneous" intracranial hypotension. Occasionally, CSF leaks occur through a dural tear caused by a cervical or lumbar disc-osteophyte complex. In contrast to idiopathic intracranial hypertension, skull base CSF leaks rarely cause SIH.

Pathology

CSF hypovolemia and hypotension (lumbar OP < 60 mm H O) result in venous and dural interstitial engorgement with brain descent ("sagging") (34-45). The dura itself typically appears normal without evidence of neoplasia or inflammation.

Longstanding cases of SIH may have dura-arachnoid fibrosis with nests of prominent meningothelial cells that should not be mistaken for meningioma.

Clinical Issues

Epidemiology and Demographics. The true incidence of SIH is unknown. Estimated prevalence is 1:50,000 per year. Although SIH can occur at any age, peak prevalence is in the third and fourth decades. There is a moderate female predominance.

Presentation. Symptoms range widely, from mild headache to coma. The classic presentation of SIH is a severe orthostatic

headache that is relieved by lying down. (Loss of approximately 10% of the total CSF volume is required to induce orthostatic headache.)

Nonorthostatic headache, nuchal rigidity, and visual disturbances are less common. Severe cases may present with progressive encephalopathy. Orthostatic or postural headache can have posterior neck pain or stiffness,vomiting, or photophobia. Hyperprolactinemia with stalk effect caused by the infundibular compression may be present.

Natural History. Most cases of SIH resolve spontaneously. In rare cases, severe unrelieved brain descent can result in coma or even death.

Treatment Options. Treatment is aimed at restoring CSF volume. Fluid replacement and bed rest can be sufficient in many cases. In others, epidural blood patch or surgical repair may be required. Emergent intrathecal saline infusion may be lifesaving in obtunded, severely encephalopathic patients.

Epidural blood patch is often performed on the basis of clinical and brain imaging findings alone. If lowand high-volume patches are unsuccessful, further studies may be necessary to localize precisely the level of the CSF leak.

INTRACRANIAL HYPOTENSION

Etiology and Pathology

•CSF hypovolemia leads to brain "sags," dural/venous sinuses increase

•Can be spontaneous (idiopathic) or acquired

Clinical Issues

•Most common symptom = headache

○± Orthostatic

•Severe intracranial hypotension can cause coma, even death

MR Findings

•Common

○Midbrain "sags" down

○Angle between midbrain, pons decreases (< 50°)

○Pontomammillary distance < 5.5 mm

○Optic chiasm/hypothalamus draped over prominent pituitary

○Diffusely thickened enhancing dura (reduced with time)

○"Fat" pituitary

•Less common

○Pons, midbrain may appear "fat"

○± Tonsils displaced downward

○Effaced cisterns/sulci

○Small lateral ventricles ± atria "tugged" inferomedially

○± Subdural collections (hygromas > frank hematomas)

○Enlarged dural sinuses with outwardly bulging (convex) margins

•Rare but important

○Ventricular angle on coronal imaging decreases

○Torn bridging cortical veins

○Subarachnoid hemorrhage, superficial siderosis

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Imaging

Although CT is often obtained as an initial screening study in patients with severe or intractable headache, MR of the brain and spine is the procedure of choice to evaluate possible SIH. A spectrum of findings occurs with SIH; only rarely are all imaging signs present in the same patient! Almost 20% of patients with clinically apparent intracranial hypotension have NO abnormal brain MR findings!

CT Findings. CT scans in SIH are often normal. The most obvious findings are subdural fluid collections. Subtle CT clues to the presence of SIH include effacement of the basal cisterns (especially the suprasellar subarachnoid space), medial herniation of the temporal lobes into the tentorial incisura, small ventricles with medial deviation of the atria of the lateral ventricles, and a "fat" pons.

MR Findings. Between 90-95% of SIH patients have one or more key findings on standard MR scans.

T1WI. Sagittal T1 scans show brain descent in approximately half of all cases (34-46). Midbrain "sagging" with the midbrain displaced below the level of the dorsum sellae, decreased angle between the peduncles and pons below 50°, shortened pontomammillary distance below 5.5 mm, and flattening of the pons against the clivus are typical findings (34-47). Caudal displacement of the tonsils is common but not invariably present.

The optic chiasm and hypothalamus are often draped over the sella, effacing the suprasellar cistern. The pituitary gland appears enlarged in at least 50% of all cases (34-46) (34-50C).

Axial scans show that the basal cisterns are effaced. The pons often appears elongated and "fat" (34-49B). Midbrain anatomy is distorted with decreased width and increased anteroposterior diameter (34-49C). The temporal lobes are displaced medially over the tentorium into the incisura. The lateral ventricles are usually small and distorted, as they are pulled medially and inferiorly by the brain "sagging" (34-48).

In cases with severe brain descent, coronal scans may show that the angle between the roof of the lateral ventricles progressively decreases (< 120°) as brain sagging increases

(34-48) (34-50).

The dural sinuses often appear distended with outwardly convex margins and exaggerated "flow voids" (34-49E). Between 15-50% of cases have subdural fluid collections (hygromas > hematomas) (34-48).

T2/FLAIR. The slit-like third ventricle is displaced downward and on axial scans appears almost superimposed on the midbrain and hypothalamus (34-49C).

T1 C+. One of the most consistent findings in SIH, seen in 8085% of cases, is diffuse dural thickening with intense enhancement. Linear dural thickening may extend into the internal auditory canals, down the clivus, and through the foramen magnum into the upper cervical canal (34-47). On axial imaging the engorged enhancing cervical venous plexuses may appear like a "draped curtain," narrowing the canal and even mimicking sarcoid or metastatic disease.

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(34-51A) T2WI in 48y woman (severe HA) shows inferiorly displaced tonsils , slumping midbrain; called Chiari 1, decompressed surgically.

Dural enhancement is time dependent and gradually decreases over time. Patients with chronic SIH may have no dural enhancement despite ongoing CSF leakage detectable on CT myelography.

T2* (GRE, SWI). Tearing of bridging veins caused by brain sagging can result in subarachnoid hemorrhage and superficial siderosis.

Spine Imaging. CT myelography (CTM) with immediate and delayed imaging is considered the gold standard for finding a CSF leak. MR of the entire spine with heavily T2-weighted sequences ("MR myelogram") can be helpful in identifying meningeal diverticula with pericyst extraarachnoid CSF.

Nuclear Medicine. In-111 DTPA, intrathecal radionuclide cisternography can detect extradural egress of tracer. SPECT/CT fusion imaging is very helpful to determine the precise spinal level responsible for the CSF leak.

Differential Diagnosis

The major differential diagnosis of intracranial hypotension is Chiari 1 malformation. In rare SIH cases, prolapse of the cerebellar tonsils can be mistaken for a Chiari I malformation (34-51). However, in Chiari I the only intracranial abnormality is displaced tonsils, which appear peg-like with vertically oriented folia. Other findings of SIH are absent. Mistaking SIH for Chiari 1 on imaging studies can lead to decompressive surgery, worsening CSF hypovolemia, and clinical deterioration!