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3.18. Evaluation of radionuclide cisternography

Static scintigraphy of the cerebrospinal fluid spaces after intrathecal application of a radioindicator is referred to as radionuclide cisternography if we examine cerebrospinal fluid dynamics in the celebral region , or as radionuclide perimyelography if we monitor the spinal region .

The evaluation of this static scintigraphy consists of two stages:

• Visual evaluation of the distribution of the radio indicator in individual projections in order to assess the permeability of cerebrospinal fluid pathways, to detect or cerebrospinal fluid fistulas and differential diagnosis of communicating and obstructive hydrocephalus.
• Creation and printing of the final report containing images and verbal evaluation, including the conclusion.

Saving studies

We perform scintigraphic examination after intrathecal application of approximately 30-50 MBq ¹⁶⁹ Yb-DTPA or more preferably ¹¹¹ In-DTPA. During radionuclide cisternography, we scan the head area at 6, 24 and possibly even 48 hours after application in the front and both side projections.

Recommended storage mode:

matrix 128 ´ 128, 16 bits, preselection min. 200,000 imp.

Picture 1: AP - 5 p.m. Picture 2: DX - 5 p.m. Picture 3: SIN - 5 p.m.

Picture 4: AP - 24 hours Picture 5: DX - 24 hours Picture 6: SIN - 24 hours

if necessary:

Picture 7: AP - 48 hours Picture 8: DX - 48 hours Picture 9: SIN - 48 hours

This order of projections corresponds to the default preset in the CISTER program, so there is no need to permute the order of projections when evaluating it.

Study evaluation

First we call the required scintigraphic study in the basic menu PROCESSING (if it consists of several studies, we select them one by one and use the "Next" command to combine them into one for evaluation). We will launch a comprehensive CISTER program - static cisternography .

Sequence of projections and visual evaluation

The display shows the accumulated images and describes the names of the projections in the default order: AP-6.h. - DX-6 p.m. - SIN-6 p.m. - AP-24.hr. - DX-24h - SIN-24.hr. - AP-48h - DX-48h - SIN-48h (Only as many images as stored have been displayed). If the order of the projections agrees and we want to keep all the images, we will answer the question of the program "Order of projections okay?" positive. Otherwise (negative answer), we specify the actual assignment of the images to the projection names on the program instructions . In this way, it is possible not only to switch the order of projections, but also to select certain images and reject others for further display, processing and documentation. If we have displayed images with the corresponding assignment of projections, a visual evaluation begins .

After application of the radioindicator by lumbar puncture, the radioactivity also spreads in the cranial direction due to the concentration gradient, ie against the flow of cerebrospinal fluid, which slows down the spread of the radioindicator and prevents its diffusion into the ventricular system. Under physiological circumstances, the radioindicator is displayed 4-6 hours after application at the magna cistern level, and 24 hours after application, the convexities of both hemispheres are displayed ; however, the radioindicator does not penetrate the ventricular system.

However, in normotensive communicating hydrocephalus , the ventricular system is well displayed as early as 5-6 hours after lumbar application, while in basal cisterns and subaraches. convex spaces are only a small part of the radioactivity. This cisternoventricular reflux, lasting 2-3 days, can be caused by a slowed outflow of cerebrospinal fluid from the ventricular system (in case of impaired cerebrospinal fluid resorption into the venous system), or by changing the pressure conditions in the chambers and subaraches. space. The circulation of cerebrospinal fluid can be significantly affected by by blocking the flow of cerebrospinal fluid to the transition of the echoes between the ventricles - then it is an obstructive hydrocephalus. However, scintigraphic images of conventional cisternography tend to be non-specific here, so the application of a radioindicator directly to the lateral ventricle is sometimes used to directly detect the site of obstruction (this scintigraphy is then referred to as cerebral ventriculography). In hydrocephalus and vacuum, cisternographic images of normal shape are observed, only a slowing of the radiolabel distribution.

In post-traumatic, post-inflammatory or post-operative conditions, the intradural space may be connected to the nasal cavity or auditory canal (intracranial dural defect) - a cerebrospinal fluid fistula is formed . Extracranial deposition of the radioindicator may then be visible on the scintigrams at 24 hours . In addition to scintigrams, however, cerebrospinal fluid can be demonstrated by measuring (eg in a well scintillation detector) the radioactivity of tampons introduced about 5 hours after application to the nasal cavities, or radioactivity of aspirated gastric juice, and compare these values ??with the radioactivity of plasma. In the case of cerebrospinal fluid fistula, the radioactivity of nasal tampons and gastric juice is significantly higher compared to the plasma sample.

This category of scintigraphic methods also includes examination of the patency of the drainage of the ventricular system in obstructive or communicating hydrocephalus, where the radioindicator is applied intraventricularly or into the drain and we monitor the distal or retrograde progression of radioactivity on scintigrams.

For the text of the visual evaluation of radionuclide cisternography we can use both the implicit standard formulation of the normal evaluation, eg:

or a non-standard free text of a pathological finding (as in Fig. 3.18.1).

Final protocol

The display then shows all selected images, and we can set their optimal modulation (LT / UT). In the box below we can edit the text of the verbal description of the scintigraphic images and the conclusion. Finally, we can print a report , containing (in addition to basic data such as the patient's name) the relevant images, the text of the verbal evaluation, conclusion and signature - Fig.3.18.1.

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