Cortical tubers or subcortical tubers (with involvement of the underlying white matter) are a common finding in tuberous sclerosis, present in 95-100% of cases 1.
These benign hamartomatous lesions can be an epileptogenic focus, and are important to diagnose on imaging (typically MRI) as they can affect treatment. In some cases of medically refractory epilepsy, cortical tubers may be surgically resectable 2,3.
Tuberous sclerosis typically presents in the first decade of life and has a reported incidence of 1:6000-12000 1 with intracranial involvement in the vast majority of patients, mainly cortical tubers or subependymal nodules.
Some cases are sporadic, although an autosomal dominant inheritance pattern has been demonstrated in tuberous sclerosis, in about 80% of cases 4.
There is significant variation in presentation of tuberous sclerosis, dependent on the distribution and burden of hamartomata throughout the body.
Cortical tubers may be epileptogenic foci, presenting with partial seizures or infantile spasms. Cortical tubers may also contribute to cognitive defects or austitic/neurobehavioural traits in some tuberous sclerosis patients 1. These symptoms were part of the original Vogt triad, and cortical tubers remain one of the major features in the diagnostic criteria for TS 5. There is an association with worse neurological outcome with greater burden of cortical tubers 6.
Cortical tubers are areas of distorted cortical architecture with abnormal cells, also involving the underlying white matter. Distinguishing these cortical tubers from focal cortical dysplasia can be difficult, often relying on ancillary findings and immunophenotyping.
Calcification can occur in tubers, but is more commonly in present in subependymal nodules. Central cystic degeneration can also occur 1.
The tubers are non-functioning as they have been removed from eloquent areas with little to no long term effects 2.
Small (<1 cm) firm nodular lesions in the cerebral cortical gray matter 7. Cerebellar lesions are typically wegde shaped, and tend not to be epileptogenic foci. Tubers are rarely found in the brainstem (without cortex).
Cortical tubers will contain varying densities of proliferative dysmorphic neurons and giant cells 3. Lower myelin content has also been demonstrated in tubers 3.
Cortical tubers, and most CNS involvement of tuberous sclerosis, are best demonstrated on MRI. 50-90% will be found in the frontal lobes 1,8.
- can show areas of calcification, although this is more commonly demonstrated in subependymal nodules
- T1: low signal
- T2/FLAIR: initally low signal, but typically high signal
- T1 C+ (Gd): only demonstrated in <10% of cases 1,8
In unmyelinated brain (neonatal cases) some tubers can be isointense on T2 sequences and can be missed, relying instead on the T1 sequences 1.
Occasionally radial bands relating to periventricular matter can be seen.
Treatment and prognosis
Treatment of symptoms arising from cortical tubers is usually required in the form of seizure control. If there is reduced cognitive function, supportive care should also be considered.
In medically refractory epilepsy (50-80% of TS cases), surgical excision of the tuber can be considered with a view to improving seizure frequency and control, and with an improvement in cognitive function 2,3.
In the clinical context of known tuberous sclerosis, the appearance is virtually pathognomonic. The presence of other findings (subependymal nodules, subependymal giant cell astrocytomas, white matter abnormalities) or extra-CNS findings will help.
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