CSF imaging

CSF imaging

1. CSF NUCLEAR IMAGING Miad alsulami

2. Objectives : To understand : physiology of CSF anatomy and CSF circulation. Radiopharmaceuticals . clinical applications of CSF imaging .

3. Introduction : Cerebrospinal fluid (CSF): is a clear, colorless body fluid found in the brain and spinal cord. It is produced by ependymal cells in the ventricles of the brain, and absorbed in the arachnoid granulations. There is about 125mL of CSF at any one time, and about 500 mL is generated every day.

4. Function of csf : CSF acts as a cushion or buffer for the brain, providing basic mechanical and immunological protection to the brain inside the skull. CSF also serves a vital function in cerebral autoregulation of cerebral blood flow.

5. LOCATION OF CSF : CSF occupies the subarachnoid space (between the arachnoid mater and the pia mater) and the ventricular system around and inside the brain and spinal cord. There is a connection from the subarachnoid space to the bony labyrinth of the inner ear via the perilymphatic duct where the perilymph is continuous with the cerebrospinal fluid.

6. Distribution of CSF: There is about 125–150 mL of CSF at any one time. This CSF circulates within the ventricular system of the brain. The majority of CSF is produced from within the two lateral ventricles.

7. Contents of CSF : CSF is derived from blood plasma and is largely similar to it, except that CSF is nearly protein-free compared with plasma and has some different electrolyte levels. CSF contains approximately 0.3% plasma proteins , or approximately 15 to 40 mg/dL, depending on sampling site. globular proteins and albumin are in lower concentration in ventricular CSF compared to lumbar or cisternal fluid. CSF is normally free of red blood cells , and at most contains only a few white blood cells.

8. Comparison of Average Serum and Cerebrospinal Fluid Substance CSF Serum Water Content (%) 99 93 Protein (mg/dL) 35 7000 Glucose (mg/dL) 60 90 Osmolarity ( mOsm /L) 295 295 Sodium ( mEq /L) 138 138 Potassium ( mEq /L) 2.8 4.5 Calcium ( mEq /L) 2.1 4.8 Magnesium ( mEq /L) 2.0–2.5 1.7 Chloride ( mEq /L) 119 102 pH 7.33 7.41

9. The brain produces roughly 500 mL of cerebrospinal fluid per day, at a rate of about 25 mL an hour. The transcellular fluid is constantly reabsorbed, so that only 125–150 mL is present at any one time.

10. HOW THE CSF PRODUCED about 80 % of CSF is produced by the choroid plexus. The choroid plexus is a network of blood vessels present within sections of the four ventricles of the brain. It is present throughout the ventricular system. The CSF is also produced by the single layer of column-shaped ependymal cells which line the ventricles.

11. filtered form of plasma moves from fenestrated capillaries in the choroid plexus into an interstitial space,with movement guided by a difference in pressure between the blood in the capillaries and the interstitial fluid. This fluid then needs to pass through the epithelium cells lining the choroid plexus into the ventricles, an active process requiring the transport of sodium, potassium and chloride that draws water into CSF by creating osmotic pressure. The epithelial cells lining the choroid plexus contain tight junctions between cells, which act to prevent most substances flowing freely into CSF.

12. Reabsorption: CSF returns to the vascular system by entering the dural venous sinuses via arachnoid granulations.

13. CSF REGULATION CSF generation are influenced by hormones and the content and pressure of blood and CSF. when CSF pressure is higher , there is less of a pressure difference between the capillary blood in choroid plexuses and CSF, decreasing the rate at which fluids move into the choroid plexus and CSF generation. The autonomic nervous system influences choroid plexus CSF secretion, with activation of the sympathetic nervous system increasing secretion and the parasympathetic nervous system decreasing it.

14. Clinical SIGNIFICANCE of CSF 1-Pressure CSF pressure, as measured by lumbar puncture, is 10–18 cmH2O (8–15 mmHg) with the patient lying on the side and 20–30 cmH2O (16–24 mmHg) with the patient sitting up. In newborns, CSF pressure ranges from 8 to 10 cmH2O (4.4–7.3 mmHg or). Most variations are due to coughing or internal compression of jugular veins in the neck. When lying down, the CSF pressure as estimated by lumbar puncture is similar to the intracranial pressure.

15. Any condition lead to abnormal accumulation of CSF in the ventricles of the brain will raise the intracranial pressure .

16. 2-CSF leak CSF can leak from the dura as a result of different causes such as physical trauma or a lumbar puncture, or from no known cause when it is termed a spontaneous cerebrospinal fluid leak It is usually associated with intracranial hypotension: low CSF pressure. It can cause headaches, made worse by standing, moving and coughing,as the low CSF pressure causes the brain to "sag" downwards and put pressure on its lower structures

17. If a leak is identified, a beta-2 transferrin test of the leaking fluid , when positive, is highly specific and sensitive for the detection for CSF leakage.

18. Caffeine, given either orally or intravenously, often offers symptomatic relief. Treatment of an identified leak may include injection of a person's blood into the epidural space (an epidural blood patch), spinal surgery, or fibrin glue.

19. ANATOMY AND CSF CIRCULATION

20. Radiopharmaceuticals Radiopharmaceuticals injected intrathecally into the lumbar subarachnoid space must meet strict standards for sterility and apyrogenicity . The intrathecal administration of radiopharmaceuticals is of even more concern than with intravenous injection since animal experiments have shown that the subarachnoid space is possibly 1000 times more sensitive to endotoxin administered intrathecally compared with that administered intravenously.

21. They should follow the flow of the CSF without affecting the dynamics, and they should rapidly clear through the arachnoid villi. non–lipid soluble, not metabolized, and not absorbed across the ependyma before reaching the arachnoid villi. Imaging in cisternography studies may extend over a period of days; radiotracer with long half- and reasonable imaging characteristics are preferable.

22. Radioiodinated serum albumin (RISA) was the first widely used tracer for CSF imaging. RISA distributes thoroughly throughout the CSF. The long half-life of iodine 131 allowed extended imaging intervals.

23. the beta emissions increased the radiation dosimetry to the patient, specifically the brain and spinal cord, and limited both the administered dose and the available photons for imaging. numerous authors reported a high rate of aseptic meningitis from its use—up to 14% in one series. This was manifested as headache, fever, chills, and nuchal rigidity, which presented within 24 hours of injection and spontaneously resolved without sequelae after 72 hours. Sterile leukocytosis was present in the CSF of 24% of the patients who developed symptoms.

24. DTPA: The radiopharmaceutical most commonly used for CSF imaging today is indium In 111 diethylenetriaminepentaacetic acid (DTPA). The high abundance of its primary photons, 171 keV (89%) and 247 keV (94%). Its 67.5-hour half-life is ideally suited for delayed imaging at 48 to 72 hours, and its radiation dose to the brain and spinal cord is 2.5 R/ mCi . It distributes in all CSF spaces and escapes the subarachnoid space only at the arachnoid villi.

25. The target-to-nontarget ratio is also higher with DTPA than with RISA; although both are absorbed into the vascular space at the arachnoid villi, the continued blood clearance of DTPA by the kidneys decreases blood background within the head, whereas RISA persists with a long vascular half-life. Rare reports of aseptic meningitis have occurred with In111-DTPA.

26. Technetium Tc 99m DTPA is successfully used in many applications, particularly in pediatric patients and for shunt patency studies. Its obvious benefits of higher availability, lower cost, low radiation dose .

27. clinical applications of CSF imagings 1- Cisternography. 2- Surgical Shunt Patency. 3- Cerebrospinal Fluid Leak. 4- leptomeningeal metastatic disease*.

28. Cisternography Used to asses the CSF circulation . Hydrocephalus is abnormal enlargement of the CSF spaces resulting from abnormalities of CSF production, circulation, or absorption .

29. Cause of hydrocephalus : 1-Obstruction to CSF flow free passage through the ventricular system and subarachnoid space (e.g., stenosis of the cerebral aqueduct or obstruction of the interventricular foramina) secondary to tumors, hemorrhages, infections or congenital malformations) and can cause increases in central nervous system pressure. 2-Hydrocephalus can also be caused by overproduction of CSF (relative obstruction) (e.g., choroid plexus papilloma, villous hypertrophy. 3-Bilateral ureteric obstruction is a rare, but reported, cause of hydrocephalus.

30. Types of hydrocephalus: 1-Communicating hydrocephalus. 2-non-Communicating hydrocephalus .

31. Communicating hydrocephalus Communicating hydrocephalus, also known as nonobstructive hydrocephalus , is caused by impaired CSF reabsorption in the absence of any CSF-flow obstruction between the ventricles and subarachnoid space. This may be due to functional impairment of the arachnoidal granulations (also called arachnoid granulations or Pacchioni's granulations), which is the site of CSF reabsorption back into the venous system.

32. CAUSES OF communicating hydrocephalus subarachnoid/intraventricular hemorrhage. Meningitis. congenital absence of arachnoid villi. Scarring and fibrosis of the subarachnoid space following infectious. inflammatory, or hemorrhagic events can also prevent resorption of CSF, causing diffuse ventricular dilatation.

33. Noncommunicating hydrocephalus Noncommunicating hydrocephalus, or obstructive hydrocephalus, is caused by a CSF-flow obstruction. Foramen of Monro obstruction may lead to dilation of one, or if large enough (e.g., in colloid cyst), both lateral ventricles. The aqueduct of Sylvius, normally narrow, may be obstructed by a number of genetically or acquired lesions (e.g., atresia, ependymitis , hemorrhage, tumor) and lead to dilation of both lateral ventricles, as well as the third ventricle.

34. Fourth ventricle obstruction leads to dilatation of the aqueduct, as well as the lateral and third ventricles (e.g., Chiari malformation). The foramina of Luschka and foramen of Magendie may be obstructed due to congenital malformation (e.g., Dandy-Walker malformation).

35. cisternography The role of radionuclide cisternography is generally reserved for situations that remain unclear. When assessing hydrocephalus, it must first be known whether the process is noncommunicating or communicating. Then the route of radiopharmaceutical administration and expected pattern during cisternography can be predicted and evaluated.

36. In noncommunicating causes of hydrocephalus , flow from the ventricular system into the basal cisterns and subarachnoid space is obstructed. This is commonly due to a mass or congenital abnormality at or above the fourth ventricle, and the diagnosis is usually made by MRI. In communicating hydrocephalus, radionuclide studies were commonly used to help assess communicating hydrocephalus patients with normal-pressure hydrocephalus to determine whether the patient would be likely to benefit from CSF shunting.

37. Normal-pressure hydrocephalus manifests clinically with progressive dementia, ataxia, and incontinence. Surgical shunting of CSF can potentially cure this cause of dementia, but not all patients improve with surgery. 111InDTPA injected intrathecally into the subarachnoid space via lumbar puncture (done in intervention suite ) .

38. 111In has a relatively long half-life (67 h) and reasonable imaging characteristics. After the injection, an initial image of the site usually confirms the correct location by visualizing the cephalad migration of radiotracer up the spinal canal . No excessive renal activity should be noted on these early images .

39. Planar views in multiple projections are typically acquired at 2, 4, 24, and 48 h. In a study with normal findings, the radiotracer should reach the basal cisterns within the first hour, the Sylvian fissure by 2–6 h, the cerebral convexities by 12 h, and the arachnoid villi in the sagittal sinus by 24 h .

40. Neptune's trident

41. Activity should be identified over the convexities of the brain by 24 hours. Normally, there is no reflux of activity into the lateral ventricles. a small amount of activity which is transiently present in the lateral ventricles within the first 24 hours is within the accepted limits of normal . Persistent activity within the lateral ventricles after 24 hours is virtually diagnostic in the proper clinical setting.

42. Several patterns of flow can be observed after introduction of radiopharmaceutical into the intrathecal space. Normal flow should not reflux into the ventricles and should move over the convexities by 24 hours . In patients with noncommunicating hydrocephalus , cisternography usually shows a normal pattern of flow up to the basal cisterns , over the convexities. No ventricular reflux is seen. However, if activity is injected into the ventricles through a ventriculostomy rather than via lumbar puncture, serial images show minimal activity in the basal cisterns.

43. The common denominator is absent flow or a marked delay of activity flow up over the convexities of the brain. Ventricular reflux of activity may occur transiently or persist . Atrophy alone will cause delayed tracer movement through the enlarged subarachnoid space, sometimes with transient ventricular reflux. normal clearance over the hemispheres is seen by 24 hours.

44. Types of CSF circulation

45. Type I, which can be either normal or seen in a noncommunicating hydrocephalus , shows radiotracer movement over the convexities at 24 h.

46. type II, there is delayed migration over the convexities, but no ventricular reflux is noted. This pattern can been seen in cerebral atrophy or in advanced age .

47. type IIIA pattern demonstrates transient ventricular reflux, with radiotracer activity over the convexities. This pattern is considered to be indeterminate, because it can be seen in either evolving or resolving communicating hydrocephalus .

48. no migration of radiotracer over the convexities at 24 h with transient ventricular activity

49. ventricular activity persists at 24 h, the pattern is type IV

50. These two patterns can support a clinical diagnosis of NPH, and patients with these patterns were once thought to benefit the most after CSF shunting, with a sensitivity of 88% in predicting a good response

51. Surgical Shunt Patency A variety of diversionary CSF shunts (ventriculoperitoneal, ventriculoatrial , ventriculopleural , lumboperitoneal ) have been used to treat obstructive hydrocephalus . Complications may include catheter blockage, infection, thromboembolism, subdural or epidural hematomas, disconnection of catheters, CSF pseudocyst, bowel obstruction, and bowel perforation.

52. The diagnosis of shunt patency and adequacy of CSF flow often can be made by examination of the patient and inspection of the subcutaneous CSF reservoir. When this assessment is uncertain, radionuclide studies with In-111 DTPA or Tc-99m DTPA are useful for confirming the diagnosis. Familiarity with the specific shunt type and its configuration is helpful. For example, the valves may allow bidirectional or only unidirectional flow.

53. A proximal shunt limb consists of tubing running from the ventricles into the reservoir, and the distal limb carries CSF away from the reservoir into the body. Shunt injection should be performed with aseptic technique by a physician familiar with the type of shunt in place, preferably the neurosurgeon .

54. Patency of the proximal shunt limb can sometimes be evaluated before checking distal patency. In patients with certain types of variable or low-pressure two-way valves , the distal catheter is initially occluded by manually pressing on the neck. The pressure may cause injected tracer to flow into the proximal limb. Images should show prompt flow into the ventricles, followed by spontaneous distal flow through the shunt catheter .

55. Resistance at the time of injection always indicates malfunction of the shunt. If there is proximal limb malfunction, either no activity will reflux into the ventricle and there will be rapid transit of the radiopharmaceutical through the distal shunt into the peritoneal cavity.

56. if the radiopharmaceutical refluxes into the ventricles— there will be slow clearing, taking several hours. If the one-way valve is located proximal to the port, the pattern will mimic a proximal shunt obstruction.

57. Obstruction of the distal limb of ventriculoperitoneal shunts is indicated by lack of free radiopharmaceutical into the peritoneal cavity or a loculated collection at the distal tip. Obstruction of the distal limb may be due to tip occlusion from fibrous adhesions, distal tubing kinking or—if the radiopharmaceutical refluxes into the ventricles—there will be slow clearing, taking several hours.

58. The shunt tubing is usually seen. Catheters draining into the peritoneum show accumulation of radiotracer freely within the abdominal cavity. In cases of obstruction, activity does not move through the distal limb on delayed images or may pool close to the tip of the catheter in a loculated collection .

59. Cerebrospinal Fluid Leak Trauma and surgery (transsphenoidal and nasal) are the most common causes for CSF rhinorrhea. Nontraumatic causes include hydrocephalus and congenital defects. CSF rhinorrhea may occur at any site, from the frontal sinuses to the temporal bone The cribriform plate is most susceptible to fracture, which can result in rhinorrhea, Otorrhea is much less common.

60. Accurate localization of CSF leaks can be clinically difficult. Radionuclide studies are sensitive and accurate methods of CSF leak detection. To maximize the sensitivity of the test, nasal pledgets are placed in the anterior and posterior portion of each nasal region by an otolaryngologist and then removed and counted 4 hours later

61. A ratio of nasal-to-plasma radioactivity greater than 2:1 or 3:1 is considered positive. After cisternography, there will always be a small, but quite variable, amount of In-111 DTPA in the plasma. Some of the plasma activity will be excreted into the mucosal cavities. it is essential to compare the pledget data with the plasma data.

62. leptomeningeal metastatic disease Identification of obstructed flow of CSF along the subarachnoid space in patients undergoing or being considered for intrathecal chemotherapy for leptomeningeal metastatic disease. Leptomeningeal metastases is complication of neoplasms , occurring in up to 5% of all malignant neoplasms; the median survival for untreated patients is 1.5 to 2 months. Forty percent to 50% of patients with leptomeningeal metastases may present with abnormal dynamics of CSF flow , represented by partial or complete obstructions of the flow pattern, most commonly at the base of the brain, along the cerebral convexities, or along the spinal canal, typically in the region of the conus medullaris or the cauda equina.

63. The radiotracer can be injected in the lumbar segment of the spinal canal with a standard lumbar puncture or, if clinically indicated, through an existing Ommaya reservoir. This can be performed, after sterile preparation of the overlying skin, access with a 25-gauge needle , and removal of approximately 2 mL of CSF , by injecting 0.5 mCi of mIn -DTPA. The catheter is then flushed with the autologous CSF previously aspirated, always in a sterile system .

64. Several authors have found radionuclide cisternography to be a sensitive method for assessment of disease burden in these patients; it is considered more reliable than contrast-enhanced MRI or CT as well as CT-myelography to Identify Compartmentalization. Compartmentalization of the CSF flow, characterized by arrest of CSF migration in regions of leptomeningeal adhesions caused by tumor. Patients without CSF flow obstructions appear to respond statistically better to intrathecal chemotherapy, with prolonged survival.

65. Normal times to appearance of 111 Indium-DTPA following intraventricular injection in either adults or children : ventricles (median 1 minute) cisterna magna/basal cisterns (5 minutes ) cervical (15 minutes ) thoracic (20 minutes ) lumbar (30 minutes ) spinal subarachnoid spaces; and sylvian cisterns (50 minutes ).

66. Normal times to appearance of 111 Indium-DTPA following intralumbar injection : lumbar (1 minute ). thoracic (22.5 minutes ). cervical (32.5 minutes ). cisterna magna/basal cisterns (37.5 minutes) sylvian cisterns (65 minutes ). ventricles (1,440 minutes ). cerebral convexities (1,440 minutes ).

67. INTRESTING CASES This Photo by Unknown Author is licensed under CC BY-NC-ND

68. CASE 1: 36 year old woman with a ventriculoperitoneal shunt presents with headache, diplopia, and seizures.

69. Initial 30-second anterior images obtained with the camera over the patient's head and neck .

70. first set only displayed at higher intensity

71. DIAGNOSIS?

72. The patient underwent a second injection, this time into the shunt reservoir.

73. Major teaching points If there is no movement of activity on a CSF shunt study, be sure to exclude the possibility of an infiltrated injection before diagnosing shunt obstruction.

74. CASE 2: 15 month old female with rhinorrhea following resection of a nasal mass.

75. Images obtined 1 hour after the injection of the radiopharmaceutical into the lumbar subarachnoid space .

76. 3hr. delayed images over the abdomen.

77. The pledgets were removed, weighed and counted in a well counter along with a simultaneously obtained plasma sample. The ratio of pledget activity per gm of accumulated fluid to that of plasma activity per ml was 40:1 in the right pledget . The ratio in the left pledget was 1.5:1.

78. DIAGNOSIS? Cerebral Spinal Fluid Leak

79. Major teaching pointS : In pediatrics Tc-99m DTPA is usually used . One of the concerns with Tc-99m DTPA is that if there is improper labelling, or dissociation of the Tc-99m, one may see gastric uptake as a result of free Tc-99m pertechnetate. The absence of thyroid and salivary gland activity indicates that this has not occurred.

80. Radionuclide cisternography is a sensitive method for the detection of active CSF leaks. The major value of radionuclide cisternography for the detection of CSF leaks is in the pledget count. Coordination between multiple departments is required for this study. Nuclear medicine performs the imaging and counting while otolaryngology is required to place the pledgets . In many institutions, neuroradiology will perform the intrathecal injection.