In this presentation, a clinical application of isotope cisternography is explained in detail. Several examples are provided. The slides are based on UPTODATE.

1. Clinical application and indications

2.  Radiopharmaceuticals
 111In-DTPA is the most commonly used
 99m-Tc-DTPA is a viable alternative however imaging past 24 hours can not be done
 The best way of introduction in to the sub-arachnoid space is lumbar puncture
 Dosage
 111In-DTPA: 0.5-1 mCi
 99m-Tc-DTPA: 3-5 mCi

3.  Posterior image of thoracolumbar spine at 15-30 minutes
 Should show linear ascent of tracer in the spinal subarachnoid space.
 Failure to see this pattern or the presence of an outline of the vertebral segments
indicates an extrathecal injection
 Rapid visualization of bladder

7.  1-2, 3-6, 24 hour imaging of the skull
 1h images show the radiotracer in the basilar cisterns
 4-6 h images show the radiotracer in the basilar cisterns as well as sylvian and
interhemispheric fissures
 24 h images cerebral convexities are reached
 48 h (not available by Tc-99m-DTPA) mainly superior sagittal sinus

13.  Can be seen on the 6h images
 Should be cleared on the 24 h images

15.  Standardized pledgets, most often 1.0 x 1.0 cm with an absorptive capacity of 0.5
mL, are placed in each nasal passage 2 hours after the lumbar administration of
the tracer.
 These are left in place for 4 hours.
 Each time the pledgets are removed, a 2-mL aliquot of blood is drawn for
comparison to account for the blood background present from absorbed tracer.
 A weight-corrected ratio of pledget to plasma counts
 Never exceeds 1.3 to 2

16.  A condition of pathologically enlarged ventricular size with normal opening
pressures on lumbar puncture.
 A classic triad of
 Dementia
 Gait disturbance
 Urinary incontinence

17.  Impaired absorption of CSF is the suspected mechanism
 The most common identified underlying causes
 Intraventricular and/or subarachnoid hemorrhage (either from aneurysm or trauma)
 Prior acute or ongoing chronic meningitis (from infection, cancer, or inflammatory
disease).
 When no cause is identified
 A previous head injury or subclinical viral meningeal infection
 Patients with NPH also may have a higher than expected prevalence and severity
of periventricular white matter disease on magnetic resonance imaging (MRI)

18.  The gold standard with which diagnostic tests for NPH are compared is a response
to ventricular shunting
 MRI or CT
 MRI is superior to CT as can show other DDx. However CT is better for screening
 Findings include
 Ventriculomegaly in the absence of sulcal enlargement
 White matter lesions
 MRI may show a characteristic high signal abnormality around the ventricles, which is
thought to represent transependymal egress of fluid.
 Aqueduct flow void
 MRI in patients with NPH frequently demonstrates loss of signal in the aqueduct of Sylvius

22.  Confirmatory tests
 Removal of CSF
 Tests measuring a clinical response to removal of cerebrospinal fluid (CSF) are appealing since
they appear to simulate a response to shunting.
 Intracranial pressure monitoring
 B-waves occurring during more than 50 percent of the recording time has been associated with a
good response to shunting in some studies
 CSF infusion tests
 Isotope cisternography

23.  Persistent ventricular reflux and delayed movement to the convexities are the
main findings

27.  Although radioisotope cisternography is able to identify communicating
hydrocephalus, it has not been shown to reliably predict outcomes from shunt
surgery

30.  Classic syndrome
 Orthostatic headache
 Low cerebrospinal fluid (CSF) pressure
 Diffuse meningeal enhancement on brain MRI
 Many non-classic cases are diagnosed
 Historically a number of other terms have been used to describe it
 ●Spontaneous (or idiopathic) low CSF pressure headache
 ●Low CSF volume headache
 ●Hypoliquorrhoeic headache
 ●Aliquorrhea
 ●CSF leak headache
 ●CSF hypovolemia
 ●CSF volume depletion

31.  CSF leak
 The prevailing etiology of spontaneous intracranial hypotension is that of CSF leakage
located in the spine, which may occur in the context of rupture of an arachnoid
membrane
 An underlying connective tissue disorder may result in dural weakness
 Meningeal diverticula, often seen in patients with CSF leaks, may be related to this
connective tissue problem
 Trauma
 A potential contributing factor
 Fall
 sudden twist or stretch
 sexual intercourse or orgasm
 a sudden sneeze
 sports activity,

32.  Low venous pressure
 The lower pressure in the inferior vena cava leads to epidural venous hypotension and
outflow of CSF along the spinal cavity, and in some cases precipitates actual CSF leaks
from existing radicular arachnoid diverticula or cysts.

33.  Is almost exclusively spinal
 most occur at the thoracic or cervicothoracic junction.
 Few, if any, cases result from CSF leaks at the skull base.
 Presents as overt rhinorrhea or otorrhea
 Epidemiology
 ●The estimated annual incidence is 5 per 100,000
 ●The peak incidence is around age 40, but children and older adults are also affected
 ●Women are affected more frequently than men, with a female to male ratio of 2:1
 Possible risk factors are connective tissue problems and bariatic surgery

34.  Headache
 The headache ordinarily develops within two hours, and in most cases within 15
minutes, of sitting or standing
 Headache relief is typically obtained with recumbency, usually within minutes
 is often described as throbbing or dull pain that may be generalized or focal
 Associated symptoms
 ●Neck pain or stiffness
 ●Nausea
 ●Vomiting

35.  Confirmation of the diagnosis requires evidence of low CSF pressure
 Most often by MRI
 Less often by radioisotope cisternography
 and/or evidence of a CSF leak on other neuroimaging studies, mainly computed tomographic
(CT) myelography.
 Brain MRI with gadolinium and MRI of the spine without gadolinium
 Diffuse pachymeningeal enhancement (image 1)
 “Sagging" of the brain
 Tonsillar descent, posterior fossa crowding (image 2)
 Dilated cervical epidural veins
 Spine MRI
 ●Extra-arachnoid fluid collections
 ●Collapse of the dural sac and engorgement of the epidural venous plexus
 ●Meningeal diverticula
 ●Extradural extravasation of fluid

38.  Once the diagnosis is confirmed, the need for further evaluation to confirm the
exact site of the CSF leak is driven by the patient’s response to therapy.
 Patients who fail adequate trials of conservative therapy and repeated epidural
blood patch treatments, may require definitive localization of the CSF leak or
leaks in order to have surgical repair.
 This is usually accomplished with CT myelography.

39.  For confirming a CSF leak.
 It is usually obtained as the next step if a CSF leak is suspected and MRI is normal or
nondiagnostic.
 The most common cisternographic abnormality in CSF leaks is the absence or paucity
of activity over the cerebral convexities
 In contrast, the presence of radioactivity over the cerebral convexities at 24 hours argues
against an active CSF leak
 Other findings suggestive of a CSF leak, though not as reliable
 Early accumulation of radioisotope within the bladder and kidneys,
 Leakage of isotope outside of the normal confines of the subarachnoid space
 Early soft tissue uptake of radioisotope.
 In a minority
 Reveals direct evidence of the exact cite of the CSF leak in the form of paradural
extravasation of radioisotope

40. Paradural activity in a patient with
spontaneous cerebrospinal fluid
(CSF) leak. Radioisotope was
intrathecally introduced at lumbar
level. Arrow points to the site of the
CSF leakage. Such localizations are
often approximate, while
determining the exact site of the
leak – especially if surgery is
considered – would call for
computerized tomography (CT)-
myelography or its variations such
as dynamic CT-myelograghy

41. Radioisotope cisternogram anteroposterior (upper
panel), right lateral view (middle panel), and
computerized tomography (CT)-myelogram (lower
panel) in a patient with high-flow cerebrospinal
fluid (CSF) leak. Sequential cisternographic
images at less than 20 minutes, at 2 hours, and at
4 hours. Note that IT-introduced radioisotope,
leaking with high flow, quickly enters the systemic
circulation and clears through the kidneys (upper
arrows) and collecting in the urinary bladder
(lower arrow at 2-hour image).
Quickly leaked radioisotope is in high
concentration in the blood before it gets a chance
to be cleared by the kidneys. As a result, patient’s
silhouette is noticeable in many of the images (the
“silhouette sign”). In later images, not enough
tracers had been left in the thecal sac to enable
meaningful imaging. Spine magnetic resonance
imaging (MRI; lower panel) shows extensive
extravasation of the contrast (arrows) related to
the high-flow CSF leak. Also note a hydromyelic
cavity at “C.”

44.  Normal: The IT-injected radioisotope remains intrathecal and expands in cephalad direction. Spinal
CSF Leak: Focal paradural radioactivity, often but not always, unilateral and typically away from the
injection site. This is the direct and the most desirable cisternographic evidence of spinal cerebrospinal
fluid (CSF) leak but not the most common finding, and additionally there are certain pitfalls.
Inadvertent Extradural or Partial Extradural Injection of radioisotope. Backwash Phenomenon, where
a fraction of the IT-injected radioisotope would egress from the injection site extradurally. Paradural
Activity Within the Meningeal Diverticula, often but not always multiple and with rounded
appearance.

45. Both anteroposterior and
posteroanterior are less than 20-
minute images. Note that there is
only a small amount of IT activity
while there is diffuse activity in the
systemic circulation having created
a robust silhouette sign and activity
in the kidneys and urinary bladder.

46. Image at 1 hour shows fuzzy
extradural activity at the lumbar
level and also the early appearance
of radioactivity in the urinary
bladder. Sequential images show
cephalad expansion of radioactivity.
Note that at 24 hours, there is
plenty of activity over the cerebral
convexities.

47. Multiple meningeal diverticula. No
definite leak could be demonstrated
on CT-myelograms done elsewhere
and at our institution.

48. Radioisotope cisternography (RIC)
showing extreme “meningeal
diverticulosis.” Note that the
diverticula are more abundant in
the thoracic area. No leak was
identified on computerized
tomography (CT)-myelography. In
this 24-hour image there is plenty of
activity over the cerebral
convexities, a finding typically
pointing away from active
cerebrospinal fluid (CSF) leak.

49.  Conservative treatment
 The most conservative treatment for spontaneous intracranial hypotension is avoidance
of the upright position, with strict bed rest and the possible addition of analgesics.
 Strategies aimed at restoring CSF volume include oral or intravenous hydration, high
oral caffeine intake, and high salt intake. Use of an abdominal binder is an additional
measure that may be helpful

50.  Epidural blood patch
 as first-line therapy for patients with spontaneous intracranial hypotension who
fulfill any of the following conditions
 ●Acute, mild to moderate headache unresponsive to a reasonable period of conservative
treatment (eg, one to two weeks)
 ●Severe headache or other disabling symptoms, regardless of duration
 ●Symptomatic for two weeks or longer at the time of diagnosis
 ●An aggressive precipitating injury (eg, a water skiing accident) as compared with a
minor or "trivial" trauma (eg, a sudden twist or stretch)
 ●A history of connective tissue disease or joint hypermobility

51.  Epidural fibrin glue
 There is only anecdotal evidence that treatment with epidural fibrin glue is beneficial for
spontaneous intracranial hypotension, and larger studies are needed before this
technique can be routinely recommended.
 Surgery
 For patients with spontaneous intracranial hypotension who have failed an adequate
trial of repeated EBP and have a clearly identified site of CSF leakage
 Continuous epidural infusion
 For patients with spontaneous intracranial hypotension who have failed an adequate
trial of repeated EBP and in whom the site of the CSF leak cannot be identified