From the Guidelines
The workup for cisterna magna abnormalities should start with a detailed neurological examination, followed by MRI as the gold standard imaging modality to evaluate posterior fossa structures and cerebrospinal fluid spaces, as recommended by the American College of Radiology 1. When evaluating the cisterna magna, it is essential to measure its anteroposterior diameter, with normal measurements typically between 3-8 mm.
- Values outside this range may indicate pathology such as mega cisterna magna (>10 mm), Dandy-Walker malformation, or arachnoid cysts.
- Additional testing, such as genetic studies, may be warranted if syndromic associations are suspected, particularly with conditions like trisomy 18 or Joubert syndrome.
- Cerebrospinal fluid analysis might be necessary if infection or inflammation is suspected. The workup should be tailored to the specific clinical presentation, patient age, and whether the finding was incidental or associated with symptoms such as headache, ataxia, or developmental delays.
- Consultation with neurology and/or neurosurgery is often beneficial for comprehensive evaluation and management planning, especially in cases where intracranial hypotension is suspected, as the pathophysiologic mechanism of headache symptoms and various neurological deficits in patients with intracranial hypotension is not well understood but likely multifactorial 1. It is crucial to note that the diagnosis of spontaneous intracranial hypotension (SIH) is challenging, and in some cases, SIH cannot be definitively diagnosed or excluded until a full diagnostic workup with invasive imaging (myelography) has been performed 1.
- The cumulative presence of intracranial findings, such as engorgement of venous sinuses, pachymeningeal enhancement, midbrain descent, superficial siderosis, subdural hygroma or hematoma, and convex superior surface of the pituitary, has been shown to correlate with a likelihood of finding a spinal leak source 1.
From the Research
Cisterna Magna Workup
- The workup for cisterna magna involves ultrasonic evaluation, particularly in neonates, to delineate the normal topography of the region 2.
- Standardized measurements for the midsagittal height of the cisterna magna and the distance of the fastigium of the fourth ventricle from the plane of the foramen magnum are essential to appreciate subtle alterations in size and/or position of these structures 2.
- In cases of isolated mega cisterna magna, prenatal diagnosis and clinical outcomes can be evaluated through a multicenter retrospective cohort study, analyzing maternal demographics, prenatal findings, delivery outcomes, and postnatal outcomes 3.
Diagnostic Criteria
- Isolated mega cisterna magna is defined as a cisterna magna >10 mm with a normal cerebellar vermis and no cystic dilation of the fourth ventricle 3.
- The mean anteroposterior diameter of the cisterna magna can be measured to assess the severity of the condition 3.
- Adults with isolated mega cisterna magna may exhibit lower performance on memory tasks and verbal fluency, but overall cognitive functioning remains normal 4.
Clinical Significance
- The prevalence and clinical significance of isolated mega cisterna magna in both fetuses and adults are not yet well defined, making it challenging to provide reliable parental counseling 4.
- Children with an enlarged cisterna magna may be at risk for mild developmental delay, particularly in cases of nonisolated enlargement 5.
- Incidental findings, including mega cisterna magna, can be discovered in patients imaged for headache disorders, highlighting the importance of careful evaluation and consideration of clinical context 6.