# Cavernous Malformations

## Overview

Cerebral cavernous malformations (CCMs, also called cavernomas or cavernous angiomas) are low-flow vascular lesions composed of sinusoidal vascular channels lined by a single layer of endothelium without intervening brain parenchyma. They occur in 0.4-0.8% of the population, may be sporadic or familial, and carry a risk of hemorrhage that varies significantly by location and hemorrhage history. Brainstem cavernomas represent a particular surgical challenge due to the eloquence of surrounding structures.

## Epidemiology and Genetics

The prevalence of CCMs on MRI studies is 0.4-0.8%, accounting for 5-13% of all cerebral vascular malformations. Approximately 80% are sporadic, usually presenting as a single lesion without family history. The remaining 20% are familial with autosomal dominant inheritance and multiple lesions. Three gene mutations are associated with familial CCM: CCM1 (KRIT1) on chromosome 7q (most common in Hispanic families), CCM2 (malcavernin/OSM) on chromosome 7p, and CCM3 (PDCD10) on chromosome 3q, which has the most aggressive phenotype and is associated with meningiomas and early-onset disease. Radiation-induced CCMs develop years after cranial radiation, especially in pediatric patients.

## Pathology

CCMs appear as well-circumscribed, lobulated, mulberry-like lesions. They consist of thin-walled, dilated sinusoidal vascular spaces (caverns) filled with blood at various stages of organization. Unlike AVMs, there is no intervening brain parenchyma within the lesion. The vessel walls lack smooth muscle and elastic lamina. A surrounding hemosiderin ring forms from chronic microhemorrhages. An associated developmental venous anomaly (DVA) is present in 20-30% of cases. The DVA is a normal variant of venous drainage and must not be disrupted during surgery.

## Natural History and Hemorrhage Risk

The overall annual hemorrhage rate is 0.7-1.1% per patient-year for incidental or unruptured CCMs. After a first hemorrhage, the annual re-hemorrhage rate increases to 4-5% per year, with temporal clustering meaning the risk is highest in the first 2-3 years after the initial hemorrhage and then decreases. Brainstem CCMs carry a higher hemorrhage rate of 2.3-6.8% per year and higher morbidity per hemorrhage event due to the eloquent location. Risk factors for hemorrhage include prior hemorrhage (the strongest factor), brainstem location, female sex, associated DVA (debated), and CCM3 mutation. Most hemorrhages are small and contained within the lesion or perilesional tissue, unlike AVM hemorrhage. Complete obliteration of the CCM by spontaneous hemorrhage and thrombosis can occur.

## Clinical Presentation

Seizures are the most common presentation for supratentorial CCMs (40-70%), resulting from hemosiderin deposition in surrounding cortex. Focal neurological deficits arise from acute hemorrhage or chronic hemosiderin-related toxicity. Headache is common but non-specific. Between 20-50% are asymptomatic incidental findings. Brainstem CCMs present with cranial nerve deficits, long tract signs, ataxia, diplopia, and facial weakness, and can be devastating even with small hemorrhages.

## Imaging

### MRI

On T1-weighted imaging, CCMs show mixed signal from blood products at various stages. The classic T2 appearance is the "popcorn" or "mulberry" configuration with a heterogeneous core of mixed signal surrounded by a complete hypointense hemosiderin ring. T2*/GRE/SWI sequences are exquisitely sensitive for detection, showing the hemosiderin ring and identifying additional small lesions not seen on standard sequences; these are essential for familial CCM screening. There is no restricted diffusion on DWI. Typically there is no enhancement, though faint enhancement may occur; significant enhancement suggests an alternative diagnosis.

The Zabramski classification describes four types: Type I shows subacute hemorrhage with a T1-bright core. Type II is the classic mixed signal with hemosiderin ring ("popcorn" appearance). Type III is chronic and T1/T2 hypointense (hemosiderin-predominant). Type IV is punctate and seen only on GRE/SWI.

| Zabramski Type | T1 Signal | T2 Signal | Description |
|---------------|-----------|-----------|-------------|
| I | Hyperintense (bright) | Hyper-/hypointense | Subacute hemorrhage |
| II | Mixed (reticulated) | Mixed with hemosiderin ring | Classic "popcorn" appearance |
| III | Iso-/hypointense | Hypointense | Chronic, hemosiderin-predominant |
| IV | Not visible | Not visible (GRE/SWI only) | Punctate, only seen on susceptibility sequences |

### CT

CT may show calcification, and acute hemorrhage is visible, but CT is not sensitive for CCM detection.

### Angiography

CCMs are angiographically occult, meaning DSA is normal with no arterial feeders and no arteriovenous shunting. An associated DVA may be visible on the venous phase.

<image>
Axial MRI comparison showing a cerebral cavernous malformation on T2-weighted imaging (classic "popcorn" appearance with heterogeneous core and complete hemosiderin ring), T1-weighted imaging (mixed signal from blood products of varying ages), and SWI sequence (prominent blooming artifact demonstrating multiple additional small CCMs not visible on conventional sequences). A familial case with multiple CCMs scattered throughout both hemispheres is shown on the SWI panel. Radiological teaching illustration with labeled features and Zabramski classification examples.
</image>

## Surgical Indications

### Supratentorial CCMs

Surgery is indicated for medically refractory epilepsy attributable to the CCM, progressive neurological deficit from recurrent hemorrhage, symptomatic hemorrhage causing mass effect, and accessible location with acceptable surgical risk. Observation is appropriate for asymptomatic, incidental, or deep-seated lesions.

### Brainstem CCMs

Surgical indications are stricter due to the eloquent location. Surgery is considered after at least 2 symptomatic hemorrhages with progressive deficit, after a single hemorrhage with significant deficit if the lesion presents at a pial or ependymal surface (making it surgically accessible), or for a growing lesion with progressive neurological deterioration. The optimal timing for surgery is the subacute phase (2-6 weeks after hemorrhage), when the hematoma cavity provides a surgical corridor and the surrounding hemosiderin-stained gliotic tissue defines the dissection plane. Observation is appropriate for deep brainstem CCMs without surface presentation, those with a single hemorrhage followed by good recovery, or asymptomatic lesions.

## Surgical Technique

### General Principles

Neuronavigation is used for precise localization. Intraoperative neurophysiology with MEPs, SSEPs, and cranial nerve EMG (especially for brainstem CCMs) is essential. Complete resection of the CCM is performed along the hemosiderin-stained gliotic plane. The hemosiderin ring should be removed if safely possible, especially for epilepsy cases since hemosiderin is epileptogenic. The associated DVA must be preserved because it provides normal venous drainage to surrounding brain; DVA sacrifice causes venous infarction.

### Brainstem CCMs

The two-point method (Bertalanffy) determines the safe entry zone based on where the CCM comes closest to the pial or ependymal surface on MRI. Safe entry zones of the brainstem include: for the anterior mesencephalon, the interpeduncular safe zone; for the lateral mesencephalon, the lateral mesencephalic sulcus; for the posterior mesencephalon, supracollicular and infracollicular approaches; for the pons, the peritrigeminal zone, suprafacial triangle, infrafacial triangle, and lateral pontine zone; and for the medulla, the posterior median sulcus, posterolateral sulcus, and olivary zone. Meticulous microsurgical technique with continuous neurophysiological monitoring is mandatory. Circumferential dissection of the CCM within the hemosiderin-lined cavity is performed, removing all visible CCM tissue to prevent recurrence.

### Epilepsy-Specific Considerations

Resection of the hemosiderin ring improves seizure outcomes. Electrocorticography (ECoG) can guide the extent of hemosiderin resection. Seizure freedom rates reach 70-90% with complete CCM plus hemosiderin ring resection compared to 50-60% with lesionectomy alone. Longer duration of epilepsy predicts worse seizure outcome after surgery.

## Radiosurgery for CCMs

Radiosurgery for CCMs remains controversial with no prospective randomized data. SRS does not obliterate CCMs (unlike AVMs) but may reduce hemorrhage risk over time. Retrospective data suggest a reduced hemorrhage rate after a 2-year latency period. Risks include radiation-induced edema, new neurological deficits, and radiation necrosis. SRS is generally reserved for deep brainstem CCMs that are surgically inaccessible and have had multiple hemorrhages.

<image>
Illustration of the brainstem safe entry zones for cavernous malformation resection. An anterior view shows the interpeduncular zone and peritrigeminal zone. A posterior view shows the suprafacial triangle (between CN IV, CN V, and the facial colliculus), infrafacial triangle (between the facial colliculus, CN IX exit, and striae medullares), and the posterior median sulcus. A lateral view shows the lateral mesencephalic sulcus and lateral pontine zone. Each safe entry zone is color-coded with the corresponding cranial nerves and brainstem structures labeled. Surgical neuroanatomical illustration.
</image>

## Clinical Pearls

SWI or GRE sequences are mandatory for evaluating CCMs because standard T1/T2 sequences miss small lesions; SWI should be obtained in all cases, especially to screen for familial CCMs. An associated DVA must never be sacrificed since it drains normal brain parenchyma and its occlusion causes venous infarction. Brainstem CCMs are best operated on 2-6 weeks after hemorrhage because the subacute hematoma cavity provides a natural surgical corridor and the hemosiderin ring defines the dissection plane. Temporal clustering of hemorrhage risk means that patients who have had one hemorrhage face the highest risk of re-hemorrhage in the next 2-3 years, which is when the risk-benefit ratio most favors surgery. CCMs are angiographically occult, so a normal DSA does not rule out a CCM; MRI with SWI is the imaging modality of choice. Multiple CCMs on MRI should prompt genetic testing and family screening because familial CCM is autosomal dominant with variable penetrance. For epilepsy cases, the hemosiderin ring should be removed when safely possible because hemosiderin is a potent epileptogenic substance and its removal significantly improves seizure outcomes.

## References
- Zabramski JM, et al. "The Natural History of Familial Cavernous Malformations." *J Neurosurg*. 1994;80(3):422-432.
- Gross BA, et al. "Brainstem Cavernous Malformations: 1,390 Surgical Cases from the Literature." *World Neurosurg*. 2013;80(1-2):89-93.
- Al-Shahi Salman R, et al. "Hemorrhage from Cavernous Malformations of the Brain: Definition and Reporting Standards." *Stroke*. 2008;39(12):3222-3230.
- Bertalanffy H, et al. "Cerebral Cavernomas in the Adult: Review of the Literature and Analysis of 72 Surgically Treated Patients." *Neurosurg Rev*. 2002;25(1-2):1-53.
- Akers A, et al. "Synopsis of Guidelines for the Clinical Management of Cerebral Cavernous Malformations." *Neurosurgery*. 2017;80(5):665-680.