Advanced Imaging Techniques for Diagnosing Intracranial Hypotension

Introduction

Intracranial hypotension (IH) refers to the drop in intracranial pressure. This change is said to be caused by pressure changes in cerebrospinal fluid (CSF). The CSF is present within the tissue that surrounds the brain and the spinal cord. It has an important role in keeping the brain function optimum and protecting it. One of the possible factors that cause a drop in CSF pressure is fluid leakage, either from the spinal cord or the brain. The fall in intracranial pressure presents itself clinically as a persistent headache. Other clinical manifestations may include nausea, fever, vomiting, and tinnitus. Diagnosing intracranial hypotension accurately is a task, as it may closely resemble other conditions such as meningitis, or pituitary adenoma. Imaging modalities such as the MRI (Magnetic Resonance Imaging) aid in prompt disease findings like enlargement of the pituitary gland, sagging of the brain, and subdural fluid accumulation. This article attempts to highlight and give a brief overview of the several imaging modalities that are used to correctly diagnose intracranial hypotension.

What Are the Clinical Features Of Intracranial Hypotension?

Intracranial hypotension has a highly rare incidence with only about 5 in 100,000 people affected annually. Young to middle-aged adults are more likely to suffer from this condition, with a predilection towards women. IH can either be primary or secondary, based on the cause. Primary IH is a result of weakened dural sacs owing to degenerative conditions. Secondary IH is caused by a reported injury to the dura mater in cases such as spinal or cranial injury, lumbar puncture, spinal anesthesia, and craniospinal trauma.

Clinically, IH is represented in the following ways:

1. Upon lumbar puncture, the pressure of CSF is found to be low, about less than 50 mm Hg.

2. The protein markers are elevated.

3. An orthostatic headache is present that seems to worsen while coughing, laughing, or breathing in the Valsalva maneuver. No amount of painkillers seems to provide relief.

4. Elevated hormone levels, such as prolactin, are reported in about 24 percent of IH patients.

5. Bleeding into the CSF may be present, as indicated by the erythrocyte and pleocytosis findings in CSF.

6. Impaired hearing, tinnitus, weakness, fever, nausea, vomiting, visual impairment, backache, and neck pain are some other clinical features that may be observed.

What Are the Imaging Techniques Used to Diagnose Intracranial Hypotension?

The primary causative factor responsible for intracranial hypotension is leakage of the cerebrospinal fluid (CSF). The CSF leak may be categorized as fast, slow, or, in some cases, absent. There are cases where no visible signs of a CSF leak are detected; however, the clinical signs and symptoms point towards the presence of intracranial hypotension. The CSF leaks are commonly observed in the thoracic region. The imaging techniques utilized are equipped to identify these leaks, along with their sources. Several modalities are used to fulfill this purpose. The first-line imaging techniques are discussed here.

1. Contrast-Enhanced Brain MRI:

This technique is especially efficient in showing any abnormalities in the brain that warrant a further evaluation of an underlying spinal CSF leak. These abnormalities include diffuse pachymeningeal thickening, sagging of the posterior fossa structures, superficial siderosis, subdural collections, and pituitary engorgement.

2. Heavily T2-Weighted Whole-Spine MRI:

Spinal leaks are possible to detect with a conventional spine MRI. However, the extradural CSF may be leaking laterally via a perineural cyst or a lateral dural defect as well. Thus, heavily T2-weighted imaging ensures the evaluation of abnormal extradural CSF leaks, even around paraspinal soft tissues.

3. Dynamic CT Myelography:

CT (computed tomography) and fluoroscopic methods are used in dynamic myelography. Even though the fluoroscopic dynamic myelography exhibits effective temporal resolution, endotracheal anesthesia may be necessary in certain cases due to respiratory motion artifacts that cause unnoticed CSF leaks in the thoracic area.

The dynamic CT technique trumps the fluoroscopic technique in terms of providing excellent spatial resolution of whole-spine images. The need for anesthesia is omitted as well. The only downside is that the patient is exposed to high doses of irradiation through this technique.

4. MR Myelography:

MR myelography can offer anatomical details about the subarachnoid space. MR myelography has several benefits over conventional radiography myelography, such as being non invasive, and not requiring ionizing radiation. The intrathecal gadolinium-based contrast agent used for MR myelography is thought to be a secure and reliable technique for finding CSF leaks. This technique is efficient in detecting slow CSF leaks that are typically incomprehensible during the early phase imaging.

How Is Intracranial Hypotension Diagnosed in Those Unable to Have an MRI?

Magnetic resonance imaging has proven its role as a vital diagnostic tool for intracranial hypotension. The inability to undergo MRI poses a significant diagnostic challenge for clinicians and radiologists. Opting for CT is the next best solution for patients who are contraindicated to use MRI. The first-line imaging techniques utilized in such cases include contrast-enhanced head CT to identify brain sagging, pachymeningeal enlargement, dural venous sinus, pituitary engorgement, and CT myelography to assist in spine imaging.

Conclusion

Intracranial hypotension, although rare, is a serious complication and, to date, poses quite a challenge to neurologists and radiologists. The advanced imaging techniques are highly underutilized, thus indicating a lower rate of prognosis. Medical science aims to inculcate these progressive imaging modalities at every hospital to improve the treatment success for the majority of these patients. Although a CSF leak is the leading causative factor of intracranial hypotension, radiologists must be aware of its incidence with no changes in CSF pressure as well. A thorough knowledge of the condition, paired with a sharp assessment of the MRI scans, can lead to a prompt and accurate diagnosis of intracranial hypotension. Misdiagnosis is highly likely to occur, owing to the close resemblance of intracranial hypotension symptoms with other life-threatening diseases.