Overview

The pineal gland and its function in hormone regulation

The pineal gland is a pine cone-shaped, endocrine gland in your brain. The pineal gland in adults weighs approximately 0.1g. The pineal gland plays a role in hormone secretion (release) and secretes melatonin. Melatonin acts as a chemical messenger and helps to regulate your sleep-wake cycle by modulating your circadian rhythm. The production of melatonin increases in response to dark environments (night-time) and less melatonin is secreted when it is light (day-time). This helps to control when you sleep.¹

What are pineal tumours?

Pineal tumours are located in the brain and are known as central nervous system tumours. Whilst these tumours begin in the pineal gland in the brain, they can sadly spread to other areas of your central nervous system, such as the spinal cord.

Anatomy and function of the pineal gland

Where is your pineal gland?

The pineal gland is located centrally within your brain, along the midline, and is attached to the roof of your third ventricle via a short stalk. Your third ventricle is a fluid-filled, funnel-shaped structure that resides within the centre of your brain.^2,3,4

What is the structure of your pineal gland?

Your pineal gland has a solid structure, with a red-grey colour.⁴ Your pineal gland is composed of cells known as pinealocytes, which are responsible for producing and secreting melatonin.²

The location of the pineal gland in the brain in relation to the cerebellum, pituitary gland, pons, medulla oblongata and the spinal cord.

Role of the pineal gland in hormone secretion, particularly melatonin

To first understand the pineal gland’s role in melatonin production we must first look at the structure that generates circadian rhythms and acts as a ‘clock’ in humans, this is known as the suprachiasmatic nucleus (SCN), which is located in the hypothalamus in your brain.

When there is light in your external environment, for example during the day, the SCN secretes a neurochemical known as gamma-aminobutyric acid which inhibits brain cells from signalling and communicating with one another (creating neuronal synapses) in another structure in your brain known as the paraventricular nucleus (PVN). The lack of neuronal synapses in the PVN means that the brain cells within your PVN do not send signals to your pineal gland, and melatonin is not made by the pinealocytes in your pineal gland.²

However, at night time when there is darkness, the SCN releases a different neurochemical transmitter known as glutamate, which has an excitatory effect on the brain cells (neurons) in the PVN, causing these neurons to signal to your pineal gland to synthesise and release melatonin.²

Importance of hormone regulation for overall health and wellbeing

Insufficient melatonin production can result in sleep disturbances due to a dysfunction of your circadian rhythm. However, a lack of melatonin production has also been noted in diseases such as Alzheimer’s disease, type 2 diabetes, severe pain and cancer.⁵

Pineal tumours: types and characteristics

Classification of pineal tumours

Pineal tumours are defined as tumours that begin in the pineal gland and are classified depending on how quickly they grow. Pineal tumours are typically uncommon, occurring in 0.5-1% of intracranial tumour cases. Pineal tumours usually occur in children and adolescents.¹²

The types of pineal tumours are as follows:

• Grade 1: Pineocytomas: these tumours are benign (non-cancerous), have slow growth and are classified as being ‘low grade’
• Grade 2/3: Pineal parenchymal tumours: these tumours typically have slow growth, but they can potentially spread to the spinal cord. They are classified as being ‘low grade’. These tumours have intermediate differentiation, which means that the tumour cells are classified as being intermediately different from normal cells
• Grade 4: Pineoblastomas: these tumours have a much faster growth rate, meaning they are classified as being ‘high grade’. They are malignant (cancerous) tumours, and they possess a high chance of evading nearby tissues.
• Germ cell tumours: these tumours can be benign or malignant, depending on the type of tumour ⁶
• Glial cell tumour: where the pineal tumour consists of cells known as glial cells ⁶
• Papillary tumour of the pineal region: these tumours are newly discovered and are thought to have originated from specialised ependymocytes (which are cells that function in cerebrospinal fluid that circulates your body)⁶
• Pineal cysts⁶

Common symptoms and diagnostic methods for identifying pineal tumours

What are the common symptoms of pineal tumours?

• Headaches
• Vomiting
• Nausea
• Experiencing difficulty when walking
• Difficulty with eye movements
• Having problems with balance

What are the diagnostic methods for identifying pineal tumours?

Imaging is one of the main diagnostic methods for identifying a pineal tumour, with both computerised tomography (CT) and magnetic resonance imaging (MRI) being utilised by healthcare professionals to determine the location, size and shape of the tumour. However, MRI scans remain the preferred neuroimaging scan for determining the type of tumour present.⁷

In conjunction with imaging techniques, biomarkers have also been used to assist in the diagnosis of pineal tumours. Detecting serum and cerebrospinal fluid (CSF) biomarkers for suspected pineal germ cell tumours or grade 2 parenchymal pineal tumours can aid with diagnosis and future treatment plans. These biomarkers include placental alkaline phosphatase and alpha-fetoprotein. Additionally, monitoring the concentration of these biomarkers is important for healthcare professionals to see how you are responding to treatment if you have a germ cell tumour.⁶

How do I cope with my pineal tumour diagnosis?

Once you receive your pineal tumour diagnosis you may experience feelings of shock, sadness or fear for example. It is important to remain well informed about what happens next concerning your treatment plan, and you may find comfort in finding a support network from your family, friends or even a brain tumour support charity.

Hormonal imbalance caused by pineal tumours

Disruption of melatonin production

There has been little research into the effects of melatonin production in those with pineal tumours. However, one study investigating melatonin production in those with pineal cysts found that pineal cysts did not affect the production of melatonin. However, removing the cyst via pinealectomy resulted in there being no pineal melatonin production.⁸

In addition, research into pineal parenchymal tumours has shown that they can result in either hypo-production of melatonin, or hyperproduction of melatonin.⁹

Influence of pineal tumours on other hormones

Germ cell tumours within the pineal tumours may secrete the hormone beta-human chorionic gonadotropin (hCG) hormone. The production of this hormone from tumours can imitate the effect of another hormone on the body, known as luteinizing hormone. More production of luteinizing hormone (or hCG mimicking the effect of this hormone) results in the production of sex steroid hormones. In those who have not yet reached puberty, this production of sex steroid hormones may initiate early puberty, known as precocious puberty.^10,11

Treatment of pineal tumours

Surgical and non-surgical treatment options

Pineal tumours can be treated via surgery. Whilst non-surgical options such as radiotherapy can be used to target ionising radiation towards the tumour to destroy the malignant cells, one research paper argues that removing the pineal tumour via surgery gives a longer survival time for the patient, which is highly desirable.^7,12

Minimally invasive surgery approaches have been used to remove pineal tumours, including endoscopic surgery which involves removing the tumour, typically for a biopsy to be conducted on the tumour tissue, to see what further treatment options should be considered. In addition, keyhole surgery is also used to treat pineal tumours and is considered minimally invasive to the patient.^12,13

Long term effects

Post-treatment care and the importance of regular follow-up

Post-treatment care is offered to those who have treatment for a pineal region tumour. This allows a doctor or healthcare professional to examine you, check in on how you are feeling, and help to answer any concerns you may have post-treatment. This can help to calm any nerves or anxieties you have. In some cases, you may also be offered an MRI scan in your follow-up visits.

Summary

• The pineal gland is a pine cone-shaped endocrine gland, located in your brain, that produces melatonin
• Melatonin is a hormone that regulates your circadian rhythm, and thus your sleep-wake cycle
• Pineal tumours include pineocytomas, pineal parenchymal tumours, pineoblastoma, germ cell tumours, glial cell tumours and papillary tumours
• Symptoms of pineal tumours include headaches, nausea, vomiting, difficulty when walking, having issues with eye movements and balance
• Diagnosis of pineal tumours includes brain scans such as MRI and CT scans, however, CSF samples may be taken to test for biomarkers to identify the type of pineal tumour
• Treatment includes radiotherapy or possibly surgery, such as keyhole surgery
• Post-treatment care is essential to ensure that your feelings after treatment can be discussed and your post-treatment health can be monitored
• Once presented with a diagnosis it is important to seek support from those close to you, or a brain tumour charity