CSF Imaging: Cisternography & Shunt StudiesIn-111-DTPA (intrathecal)

Quick Answer

Radionuclide CSF studies use an intrathecally injected tracer (In-111-DTPA) to follow cerebrospinal-fluid dynamics. Three roles persist: localizing a CSF leak (rhinorrhea/otorrhea — with nasal/aural pledgets counted for activity), assessing shunt patency, and demonstrating the normal-pressure hydrocephalus (NPH) pattern of ventricular reflux with delayed convexity clearance. Imaging is delayed and sequential (up to 48–72 h) because CSF turnover is slow.

Definition & Role

Cisternography images CSF circulation after intrathecal tracer injection. It answers physiologic questions — where fluid is leaking, whether a shunt flows, and whether CSF dynamics show the NPH pattern — that anatomic imaging alone cannot, though it is now used selectively alongside high-resolution CT/MRI.

Physiology of CSF Flow

CSF is produced mainly by the choroid plexus, circulates from the ventricles through the basal cisterns, ascends over the cerebral convexities, and is absorbed at the arachnoid granulations. Normally, intrathecal tracer ascends over the convexities to the granulations by ~24 hours without entering the lateral ventricles. Turnover is slow, dictating delayed, sequential imaging.

Clinical Indications

• CSF leak (rhinorrhea/otorrhea) localization and confirmation.
• Ventriculoperitoneal / other shunt patency assessment ("shuntogram").
• Normal-pressure hydrocephalus — supportive physiologic pattern.

Technique

• Intrathecal In-111-DTPA via lumbar puncture (In-111's ~2.8-day half-life suits the delayed 24–48–72 h imaging).
• Sequential imaging (e.g. ~1, 3, 6, 24, ± 48–72 h).
• CSF leak: place pledgets in the nares/nasopharynx (and ear) before/after injection; count pledget activity vs serum to localize and lateralize a leak, correlating with high-resolution CT.
• Shunt study: inject tracer into the shunt reservoir; normal flow through the distal catheter confirms patency (a shorter-lived tracer such as Tc-99m-DTPA may be used).

Interpretation

• Normal: convexity ascent by ~24 h, no ventricular entry.
• NPH: early entry and persistence of tracer in the lateral ventricles (ventricular reflux) with delayed ascent/clearance over the convexities at 24–48–72 h.
• CSF leak: skull-base activity with positive pledget counts (localizes/lateralizes).
• Shunt obstruction: stasis / absent distal flow.

Reporting Checklist

• State the time course of tracer distribution (convexity ascent, ventricular entry).
• For leaks, report pledget-to-serum ratios and side, correlated with CT.
• For shunts, state distal-catheter flow (patent vs obstructed).
• Explicitly note that the NPH pattern is supportive, integrated with the clinical triad and MRI.

Common Pitfalls

• Intermittent leaks missed if not actively leaking during the study.
• Technical injection issues (subdural/epidural placement) producing a non-diagnostic distribution.
• Treating the NPH pattern as definitive — it is supportive, not diagnostic on its own.
• Under-appreciating slow CSF turnover (inadequate delayed imaging misses the pattern).

Board Pearls

Intrathecal tracer normally ascends over the convexities to the arachnoid granulations by ~24 h without entering the lateral ventricles. The cisternographic hallmark of normal-pressure hydrocephalus is the opposite: ventricular reflux with delayed clearance over the convexities at 24–48–72 h.

For a CSF leak, skull-base activity with counted nasal/aural pledgets confirms and side-localizes rhinorrhea/otorrhea (correlate with high-resolution CT); a shunt study injects the reservoir and checks distal flow (patent vs obstructed).

Imaging is delayed and sequential because CSF turnover is slow; intermittent leaks may be missed if not actively leaking during the study, and subdural/epidural injection produces a non-diagnostic distribution. The NPH pattern is supportive, not definitive — integrate with the clinical triad (gait, cognition, incontinence) and MRI.

Related Pages

• Related CNS: Brain FDG & dementia imaging (NPH is a reversible-dementia mimic), brain perfusion agents.
• Pitfalls: Pearls, pitfalls & normal variants.

Figure / Diagram Suggestions

• A normal vs NPH cisternographic sequence (convexity ascent vs ventricular reflux/delay).
• A CSF-leak pledget setup schematic (nares/ear placement, count comparison).
• A shuntogram flow diagram (reservoir injection → distal catheter).

Self-Check (Board-Style)