Neurosurgery Diagnostic Techniques

Introduction

• Diagnostic techniques in neurosurgery have advanced with technological breakthroughs.
• These tests are used to screen, confirm diagnoses, and assist in treatment planning.
• Clinical acumen is still crucial.

Diagnosis

• A combination of history, examination, and investigation is necessary for diagnosis.

Properties of a Diagnostic Tool

• Easy to use
• Non-harmful, non-carcinogenic, and non-allergic.
• 100% sensitive and 100% specific.
• No ideal radiological tool exists.

Classification of Diagnostic Techniques

• Radiological: Plain X-ray, ultrasound scan, computed tomography (CT) scan, magnetic resonance imaging (MRI), positron emission tomography (PET), radionuclide study.
• Non-radiological: Cerebrospinal fluid analysis, hormonal assay, tumor markers, nerve conduction studies.

Plain X-Ray

• Common investigation.
• Useful for identifying fractures, dislocations, deformities, and infections.
• Skull and spine X-rays are frequently requested.
• Skull X-rays: AP and lateral views.
• Spine X-rays: Cervical, thoracic, and lumbosacral spines.
• Abnormalities to look for on skull X-ray include: linear or depressed fractures.

Computed Tomography (CT) Scan

• Indications:
  • Diagnosis of acute neurosurgical lesions in the head and spine, including skull and spinal fractures.
  • Intracranial hemorrhage (extradural hematoma, subdural hematoma, intracerebral hematoma).
  • Brain edema (due to trauma or other causes).
  • Mass lesions, such as tumors and brain abscesses.
  • Hydrocephalus.
  • Stroke.
• Advantages:
  • Better than MRI for diagnosing bone-related pathologies like fractures and bone tumors.
  • Better for acute hemorrhagic lesions.
  • Faster than MRI (few minutes), making it suitable for critically ill patients.
• Disadvantages:
  • Uses ionizing radiation.

Magnetic Resonance Imaging (MRI)

• Indications:
  • Intracranial tumors.
  • Cerebral abscess.
  • Arteriovenous malformations.
  • Venous sinus thrombosis.
  • Craniospinal abnormalities, such as the Chiari malformation.
  • Syringomyelia.
  • Spinal tumors.
  • Disc prolapse (cervical, lumbar, and dorsal).
  • Spinal canal stenosis (lumbar or cervical stenosis) and cervical myelopathy.
• Advantages:
  • Superior to CT for sellar pathology (pituitary), posterior fossa tumors (cerebellar and brainstem tumors), and spinal cord pathology.
  • Non-invasive myelography capability.
  • Can diagnose infarction within a few hours.
  • No ionizing radiation, allowing for safe repetition.
• Disadvantages:
  • Metallic foreign bodies in the body (plating and screwing, shells, cardiac pacemakers, intracranial clips) can interfere with MRI.
  • Claustrophobia.
  • Gross obesity.
  • Uncontrolled movement disorders (Parkinson's disease).
  • Respiratory disease requiring assisted ventilation or carrying risk of apnea.

Positron Emission Tomography (PET) Scan

• Used to map tissue biochemistry and physiology (functional test).
• Commonly used PET tracer is labeled glucose (Fludeoxyglucose (18F) (FDG).
• Useful in differentiating ischemic from neoplastic areas.

Cranial and Spinal Angiography

• Provides images of blood vessels.
• Used to diagnose:
  • Arteriovenous malformations.
  • Intracranial aneurysms.

Ultrasound Scan (USS)

• Transfontanelle USS:
  • Detects hydrocephalus and intracranial bleeds.
• Doppler Scan:
  • Used for carotid studies.
• Advantages:
  • Simple, fast, and non-radiation based.
• Disadvantages:
  • Observer-dependent.

Non-Radiological Techniques

Cerebrospinal Fluid (CSF) Investigation

• CSF can be obtained through spinal or cranial punctures.
• Spinal puncture (lumbar puncture): Most safely accessed in the lumbar cistern, where the spinal cord ends in the cauda equina (between the first and second lumbar vertebrae).
• Indications:
  • Suspected meningitis.
  • Subarachnoid hemorrhage (SAH).
  • Cytology in neoplastic diseases.
  • Measurement of intracranial pressure (ICP).
  • Therapeutic CSF aspiration (pseudotumor cerebri).
  • Conventional myelography via contrast injection.
  • Spinal anesthesia.

Lumbar Puncture

• Indications:
  • Suspected meningitis.
  • Subarachnoid hemorrhage (SAH).
  • Cytology in neoplastic diseases.
  • Measurement of intracranial pressure (ICP).
  • Therapeutic CSF aspiration (pseudotumor cerebri).
  • Conventional myelography via contrast injection.
  • Spinal anesthesia.
• Contraindications:
  • Raised intracranial pressure (except pseudotumor cerebri).
  • Features suggestive of raised ICP, including focal neurological deficit, recent seizure, papilloedema.
  • Sepsis at the site of the LP.
  • Bleeding tendency (coagulopathy and thrombocytopenia).
  • Abnormal respiration.
  • Vertebral deformities (kyphosis and scoliosis).
  • Total spinal block.
  • Obstructive hydrocephalus.
• Complications:
  • Post-spinal headache.
  • Cerebellar tonsillar herniation (if there is raised ICP).
  • Injury to neural structures.
  • Back pain.
  • Infection and meningitis.
  • Implantation of cutaneous tissue, leading to an epidermoid cyst.
  • Bleeding.
• Measurement of intracranial pressure.

Hormonal Studies

• Used to investigate sellar and parasellar pathologies (pituitary tumors, craniopharyngioma, tuberculum sellar meningioma).
• Hormones measured:
  • Prolactin.
  • ACTH.
  • Cortisol.
  • TSH, T3, T4.
  • GH.

Tumor Markers

• Used in pineal region tumors.
• Markers measured:
  • Beta-HCG.
  • Alpha fetoprotein.
  • Placental alkaline phosphatase.

Conclusion

• Diagnostic tests are essential for managing patients in neurosurgery.
• A combination of history, examination, and investigation is crucial for reaching a diagnosis.