26 Colloid Cyst of the Third Ventricle

Case 26 Colloid Cyst of the Third Ventricle

Remi Nader

Fig. 26.1 (A) T2-weighted axial magnetic resonance image (MRI) at the level of the foramen of Monroe. (B) Corresponding T1-weighted MRI with contrast. (C) Coronal and (D) midsagittal MRI with contrast.

Clinical Presentation

A 37-year-old woman presents with history of headaches and head pain for 3 months.

Previous history of migraines over several years.

She also has some dizziness and gait ataxia by history that started 3 months ago.

Neurologic examination shows no deficits.

Magnetic resonance imaging (MRI) scan of the brain with contrast is shown in Fig. 26.1.

Questions

Interpret the MRI.
Give a differential diagnosis of the lesion observed.
What is your initial management?
Would you resect the mass? Why or why not?
What are the different approaches for surgical treatment and which one is the preferred option in this case?
Describe your approach to resection of the lesion. Given a skull, show the landmarks for the skin incision, burr holes, and craniotomy flap. Describe all important structures encountered along the way.
What are the important potential complications and what do you do to avoid them?

Answers

Interpret the MRI.

MRI shows a lesion in the anterior 3rd ventricle at the level of the foramen of Monroe.
The lesion is ~1 cm in size, circular, homogeneous with thin rim enhancement. It is hypointense on both T1- and T2-weighted sequences. It appears to be abutting on both fornices and the internal cerebral veins (see sagittal view). It is in the midline.
There is no evidence of hydrocephalus or ventriculomegaly.

Give a differential diagnosis of the lesion observed.

Anterior 3rd ventricle lesion (mnemonic is “SACHMO”)1,2

Colloid cyst is the most likely diagnosis.

Sellar mass

Metastases

Other less likely lesions: aneurysm, abscess, hypothalamic glioma, histiocytosis, meningioma, optic glioma, sarcoidosis
What is your initial management?
- Discuss treatment options with the patient
- If she elects to have surgery then obtain:
  - Imaging: MRI frameless stereotaxy protocol
  - Laboratory studies: complete blood count, electrolytes, prothrombin time/partial thromboplastin time, type and cross match 2 units of packed red blood cells
- Ventriculostomy placement is not needed as there is no evidence of hydrocephalus.
Would you resect the mass? Why or why not?
- The patient is symptomatic from the mass (headaches, gait ataxia, etc.).
- There is no medical treatment for colloid cysts.
- It is therefore reasonable to offer her surgical treatment.
- Best approach would be to present to her the options of observation versus surgical intervention, explain the risks and benefits of both, and let the patient decide.²
What are the different approaches for surgical treatment and which one is the preferred option in this case?
- Transcallosal approach³
  - Preferred over transcortical, in general
  - Good if ventricles are small
  - Advantages:
    - Short trajectory to 3rd ventricle
    - No cortical transgression
    - Can see both foramina of Monro
  - Complication
    - Weakness
    - Akinetic mutism
    - Memory deficits
  - Preferred approach in this case, given small size of ventricles. Note: This is the approach of choice if surgeon has limited experience with the endoscope.
- Endoscopic approach^4,5
  - Less invasive than open craniotomy
  - Direct vision
  - Good decompression using endoscopic rongeurs
  - Shorter operation and hospitalization
  - Lower incidence of postoperative seizures than transcortical approach
  - Disadvantages
    - Better if ventricles are dilated
    - Poor control of bleeding
    - Cortex/brain matter may be too thick for penetration
- Transcortical, transventricular approach⁵
  - Good for anterior superior 3 rd ventricle lesions
  - Especially if lesion extends into frontal horns
  - Trajectory through the right middle frontal gyrus (F2)
  - Disadvantages
    - Higher risk of seizures (11%)
    - Need larger ventricles
- Subfrontal approach⁵
  - Best for lesions in the anterior-inferior 3 rd ventricle such as craniopharyngiomas
  - Four different corridors to enter
    - Subchiasmal
    - Opticocarotid
    - Lamina terminalis (if there is a prefixed chiasm)
    - Transfrontal–transsphenoidal (if there is a prefixed chiasm)
- Stereotactic aspiration (± endoscopic guidance)⁵
  - Good if patient is not a candidate for craniotomy
  - Good for cysts >1 cm and not very viscous
  - Enter just anterior to right coronal suture
- Ventriculoperitoneal shunt placement⁵
Describe your approach to resection of the lesion. Given a skull, show the landmarks for the skin incision, burr holes, and craniotomy flap. Describe all important structures encountered along the way.
- Interhemispheric transcallosal approach^3,6,7
- Preparation
  - Frameless stereotaxy
  - Review venous anatomy on MRI/magnetic resonance venography to check for cortical vein locations as they enter the superior sagittal sinus.
  - Position the patient supine with the head in neutral position.
  - Head of bed slightly elevated
  - Medicate with preoperative antibiotics, dexamethasone, and mannitol.
- Opening
  - ¾ suttar incision (i.e., bicoronal)
  - Open more on the right side than on the left; preserve temporalis fascia and pericranium tissues
  - Expose coronal, sagittal sutures, and bregma.
  - Lateral exposure up to the temporalis muscle insertion
  - Burr holes: Two behind and two in front of the coronal suture, 6 cm apart. Straddling the superior sagittal sinus (SSS), in front, and ‧ behind the coronal suture
  - Trapezoid bone flap – cut last the part that is straddling the SSS.
- Dissection
  - Open dura in “C”-shaped fashion based on the SSS.
  - Visualize bridging veins; avoid or dissect with microdissectors to create room for interhemispheric approach.
  - Gently place retractors on the right frontal lobe and the falx toward the left side. Be careful not to occlude the SSS.
  - Dissect your way down the interhemispheric fissure. You will identify the cingulate gyrus, callosomarginal and pericallosal arteries, corpus callosum (white structure).
  - Open the corpus callosum just distal to the genu, ~2 × 1 cm, as close to the midline as possible.
- 3rd ventricle approaches (Fig. 26.2)⁸
  - Identify which lateral ventricle has been entered.
  - Choroid plexus goes forward in the choroidal fissure to the foramen of Monro (which is medial), where it converges with the thalamostriate vein.
  - The septal and caudate veins approach the foramen from anterior.
  - With colloid cysts, the foramen of Monro may be hard to recognize initially as it will be plugged with the cyst, which is slightly grayer than the ependymal lining of the ventricle.
  - Interforniceal approach
    - Danger of permanent short-term memory loss if both fornices damaged
- Lateral ventricular approach through the foramen of Monro
  - May enlarge the foramen of Monro by opening the foramen laterally or posteriorly (sacrificing the thalamostriate vein), which is supposedly well tolerated
- Closure
  - Consider leaving ventricular catheter in place, tunneled through one of the burr holes.
What are the important potential complications and what do you do to avoid them?
Complications include^3,6,7
- Venous infarction
  - Sacrifice of critical cortical draining veins
    - Avoid through preoperative planning and imaging review
  - Sagittal sinus thrombosis leading to venous infarction
    - Retraction injury: avoid excessive retraction; keep moist
    - Injury during opening of the bone flap above the sinus
    - Overuse of coagulation in the region of the sinus
    - Hypercoagulable state of the patient, including dehydration
- Bilateral cingulate gyrus retraction or thalamic injury
  - Transient mutism
  - Care must be taken when retracting deeper structures
- Injury to the fornices
  - Injury to both fornices may result in short-term memory deficits and inability to learn new knowledge.
  - Avoid taking both fornices
- Other potential complications
  - Hemiparesis from injury to the motor cortex
  - Seizure
  - Arterial injury to pericallosal or callosomarginal arteries with infarction of the regions supplied by these vessels
  - Disconnection syndrome from wider opening of the corpus callosum
  - Internal cerebral vein injury via coagulation
  - Intraventricular hemorrhage from inadequate hemostasis
  - Other systemic problems: infection, myocardial infarction, deep vein thrombosis, pulmonary embolism, etc.