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Hypothalamic hamartomas, also known as tuber cinereum hamartomas, are benign non-neoplastic heterotopias in the brain that typically occur in the region of the hypothalamus, arising from the tuber cinereum, a part of the hypothalamus located between the mammillary bodies and the optic chiasm.
Symptoms often begin in early infancy and are progressive, often with general cognitive and functional disability.
Lesions can cause gelastic seizures, visual problems, early onset of puberty and behavioral problems 3.
Gelastic seizures are typically of short duration (2-30 seconds) and characterized by uncontrollable laughter, without impairment of consciousness, which contrasts with frontotemporal gelastic seizures that are usually longer lasting and can result in loss of consciousness 4. Very rarely children with hypothalamic hamartomas can enter into 'status gelasticus' 4.
Although an association with Pallister-Hall syndrome has been described, in general, hypothalamic hamartomas are isolated lesions 5.
Central precocious puberty is also frequently encountered in these children, typically in patients with sessile tumors. It results from over-secretion of gonadotropin-releasing hormone (GnRH) which in turn results in overproduction of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) 5.
A hamartoma is a focal malformation that resembles (but is not) a neoplasm (cf. other CNS neoplasms); it is not a malignant tumor, and it is composed of tissue elements normally found at that site that grow in a disorganized mass.
Histologically, hypothalamic hamartomas resemble normal hypothalamic neurons, although some dysplastic neurons and glial cells have also been described 3. They are thought to arise from anomalous neural migration between 35 and 40 days in utero (time of hypothalamic formation).
The most commonly used classification is morphologic, dividing hypothalamic hamartomas into either sessile or pedunculated morphology 3,5:
On conventional axial CT images, the diagnosis can be challenging, depending on slice position and thickness, although with more recent volumetric scans with coronal and sagittal reformats, the abnormality is easier to identify.
It appears as a nodule of soft tissue of similar attenuation to the adjacent brain, without calcification or contrast enhancement.
Occasionally, it may show suprasellar calcifications, an eroded dorsum sellae, or enlarged pituitary fossa 6.
MRI is the modality of choice for the assessment of this region.
Although historically they were said to have signal intensity similar to normal cortex on all sequences, this is in fact not true in most cases 7.
- hypointense to the cerebral cortex (74%) 7
- T1 C+ (Gd): no contrast enhancement
- hyperintense to the cerebral cortex (93%) 7
- hyperintensity is more conspicuous on FLAIR
- the higher the proportion of glial cells, the higher the T2 signal 3
- reduced NAA/Cr
- increased myoinositol 3
- increased Cho/Cr compared to the amygdala has also been reported 3
Treatment and prognosis
They are benign lesions and typically do not grow, however, symptomatology can be progressive 3.
Children with central precocious puberty can be treated medically.
Intractable epilepsy can respond to surgery (resection or disconnection, depending on the morphology of the tumor) and this can be performed via an open craniotomy or more recently via an endoscope 5.
Gamma knife radiosurgery has also been used 5.
History and etymology
- tuber cinereum from the Latin meaning ash-colored mass. This stems from its color, as it is composed of grey matter
- the word hamartoma derives from the greek “hamartia”: in Greek tragedy, the concept of “hamartia” is an error in judgment or unwitting mistake, normally applied to the actions of the hero; in the same view, in medicine, hamartoma is considered an error of development
- gelastic is a term often used in medical terminology to indicate an association of a symptom or syndrome with laughter; the word originates from the Greek “gelaein”, which means “to laugh”
The differential diagnosis is broadly that of suprasellar/hypothalamic lesions, although the imaging characteristics of hypothalamic hamartomas significantly reduce the differential.
Hypothalamic-chiasmatic glioma is the main differential. Most other lesions encountered in the region either have markedly different signal intensity or demonstrate enhancement.