109 Corpus Callosotomy for Drop Attacks

Case 109 Corpus Callosotomy for Drop Attacks

Abdulrahman J. Sabbagh, Jeffrey Atkinson, Jean-Pierre Farmer, and José Luis Montes

Clinical Presentation

A 14-year-old right-handed girl was diagnosed with multifocal epilepsy since the age of 4 years.
Her epilepsy has become progressive with time and has been intractable for the past 3 years.
Her seizures are described as staring events that occur 2–4 times a day and atonic drop attack that occur once or twice daily despite compliance with triple therapy.
She is on three antiepileptic medications, without which she has frequent generalized tonic clonic seizures.
On examination she is somewhat cognitively subnormal. She has multiple scalp scars of different ages from repeated falls.

Questions

How would you investigate this case?

Magnetic resonance imaging (MRI) of the brain was essentially normal. Electroencephalography (EEG) showed bilateral multifocal epilepsy.
What are the surgical options?
What would you tell the parents regarding expected seizure outcome after surgery?
What are the predictors of a better outcome?

You operate on her and perform an anterior two-thirds corpus callosotomy. Postoperatively she is well and awake but would not interact or speak for the first few days. She returns to her normal self by the end of the week.
The parents were concerned; what do you tell them happened?
What are the possible complications related to corpus callosotomy?
What are the indications for corpus callosotomy?
Describe the parts of the corpus callosum.
Compare the callosotomy procedure with vagal nerve stimulation.
What are the approaches for corpus callosotomy?

Answers

How would you investigate this case?

Investigations include the following:
- Drug levels to check compliance
- Single photon emission tomography (SPECT) scans
  - Ictal mode
  - Interictal mode
- MRI brain
- Video electroencephalogram telemetry

What are the surgical options?

Surgical options for intractable multifocal epilepsy include 1–3

Corpus callosotomy

Anterior two-thirds callosotomy

Complete callosotomy (not recommended for almost normal children)

Vagal nerve stimulator
What would you tell the parents regarding expected seizure outcome after surgery?
- This surgery is palliative.
- It is more effective in treating atonic or drop attacks compared with other epilepsy types.^1,2
- A meta-analysis/systematic review of the literature showed that the long term seizure outcome is 35% of patients with callostomy become free of most disabling seizures.⁴
What are the predictors of a better outcome?
- Factors predicting better chance of improvement include the following:
  - Lateralization
  - Frontal origin of seizures
  - Extent of corpus callosum resection^1,5,6
The parents were concerned; what do you tell them happened?
- She has developed the expected postcallosotomy transient mutism.7
What are the possible complications related to corpus callosotomy?
- Postoperative complications are as follows:
  - Mortality risk is less than 1% and morbidity rates are 6–30%.^6,8,9
  - The callosal syndrome includes^8,10,11
    - Inability to name objects presented briefly to the left visual hemifield
    - Left hemialexia
    - Left hemianomia
    - Difficulty imitating the hidden other hand
    - Unilateral tactile anomia
    - Unilateral left agraphia
    - Right-hand constructional apraxia (inability to copy a complex design with the right hand, but ability to outperform this by using the left hand)
  - Interhemispheric retraction
    - Supplementary motor area injury
    - Cingulate gyrus injury
  - Vascular compromise or injury to the following:
    - Superior sagittal sinus hemorrhage or occlusion
    - Pericallosal and supramarginal artery injury
  - Disconnection syndrome⁷
What are the indications for corpus callosotomy?
- Callosotomy is a palliative treatment aimed at seizure reduction rather than seizure cure.
- It is indicated for intractable multifocal epilepsy that is not amenable to resection of an epileptic focus and that is associated with drop attacks.^1,2
- Such examples include patients with severe Lennox–Gastaut syndrome.
Describe the parts of the corpus callosum.
- Parts of the corpus callosum are described below (Fig. 109.1).
  - Rostrum
  - Genu
  - Body
  - Isthmus
  - Splenium
  - Forceps minor and major
- Figure 109.1 also shows the approximate locations of connecting fibers of major cortical brain regions.¹²
Compare the callosotomy procedure with vagal nerve stimulation.
- Better seizure control can be achieved by callosotomy, especially drop attacks.³
- Vagal nerve stimulation is less invasive.
- Vagal nerve stimulation is reversible unlike callosotomy.
- Vagal nerve stimulation has less morbidity.
- Vagal nerve stimulation requires battery changes and a closer follow-up.³
What are the approaches for corpus callosotomy?
- Standard anterior two-thirds callosotomy1 or complete callosotomy²
  - Supine position
    - Slight flexion with placement of the midline of the cranium at a right angle to the floor
    - Single or double skin openings (anterior and posterior)
    - Interhemispheric approach by entering the cranium at the nondominant hemisphere and/or the side with the least crossing superior sagittal sinus tributaries obstructing the way (neuronavigation is very helpful in outlining those vessels preoperatively).¹³
  - Lateral position (Olivier technique¹)
    - Letting the side of entry inferior, so the brain will sag with gravity to help open the interhemispheric fissure without retraction (Fig. 109.2)
- Two-stage approach¹³
  - Starting with the two-thirds callosotomy approach and planning for the remaining one-third at a second stage if seizures need better control despite improvement.
- Other techniques
  - Endoscopic approach¹⁴
  - Gamma knife or other forms of radiosurgery¹⁵