Cerebral cavernous malformations (CCMs) may exist without apparent symptoms. Obvious symptoms tend to occur when recurrent episodes of bleeding or blood clot formation lead either to seizures, for upper lobe CCMs, or to focal or vision issues, for CCMs in the brainstem, basal ganglia and spinal cord.

Generally, signs and symptoms of CCMs may include weakness, numbness, difficulty speaking, difficulty understanding others, unsteadiness, vision changes or severe headache. Seizures also can occur, and neurological issues can progressively worsen over time with recurrent bleeding (hemorrhage). Repeat bleeding can occur soon after an initial bleed or much later, or a repeat bleed may never occur.

Most CCMs occur as a single formation, without an apparent cause and without any family history.

However, roughly 20 percent of affected people have a familial (inherited) form of the disorder. In many cases, such people can identify similarly affected family members, most often with multiple malformations. A diagnosis of the inherited form can be confirmed by genetic testing.

As mentioned above, while most CCMs occur with no clear cause, the genetic (inherited familial) form of the condition can cause multiple cavernous malformations, both initially and over time.

To date, research has identified three genetic variants responsible for familial cavernous malformations, to which almost all familial cases of cavernous malformations have been traced.

The most concerning complications of CCMs stem from recurrent bleeding (hemorrhage), which may lead to progressive neurological damage.

Hemorrhages are more likely to recur in people with prior diagnosed hemorrhages. They're also more likely to reoccur with malformations located in the brainstem.