What is Neurohypophysis?

The neurohypophysis or the back part of the pituitary gland is a structure found at the base of your brain. It developed from a layer in the embryo called the infundibulum. The neurohypophysis has two main parts: the pars nervosa and the infundibular stalk. Sometimes, two more parts, the pars intermedia and the median eminence, are also included.

This part of your pituitary gland makes two important hormones called oxytocin and vasopressin (also known as antidiuretic hormone or ADH because it stops your body from making too much urine). These hormones are actually made in a part of your brain called the hypothalamus, more specifically in areas called the paraventricular nuclei and supraoptic nuclei. From there, the hormones are moved to the neurohypophysis where they are stored until needed. When required, they are released into small blood vessels called capillaries that carry them into your bloodstream.

When the back part of the pituitary doesn’t work properly, it affects the balance of hormones in your body. This can cause health problems like diabetes insipidus (which makes you urinate a lot) and the syndrome of inappropriate antidiuretic hormone secretion (which makes your body retain too much water). Problems caused by a lack of oxytocin are less common, but can affect pregnancy and breastfeeding.

The posterior pituitary also includes special support cells called pituicytes, which help release the hormones. A tumor made from these cells is known as a pituicytoma.

What Causes Neurohypophysis?

The neurohypophysis, or the back part of your pituitary gland, can stop working properly due to various reasons.

One of these reasons can be tumors. These can include a pituitary adenoma, glioma in the hypothalamus area of the brain, craniopharyngioma, pituicytoma, granular cell tumors, and germ cell tumors.

Brain injuries as a result of accidents or a surgical procedure can also cause issues with neurohypophysis function.

Imbalances in your metabolism, as well as additional inflammatory conditions – like sarcoidosis, multiple sclerosis, and inflammation of the pituitary gland (pituitary hypophysitis), can negatively impact your neurohypophysis.

Infections such as meningitis, encephalitis, AIDS, an abscess, or septic shock, can also lead to dysfunction of the neurohypophysis.

Events that could cause bleeding in the brain, like a subarachnoid hemorrhage, problems with oxygen delivery such as occurs in Sheehan’s syndrome, pituitary apoplexy, cardiac arrest, or water on the brain (hydrocephalus) can impair the neurohypophysis.

Other potential causes may include issues such as anorexia, congenital conditions like Pituitary stalk interruption syndrome, and genetic conditions like Prader–Willi syndrome and Multiple endocrine neoplasia-1.

Lastly, several medications can affect the functioning of the neurohypophysis. These include Phenothyazides, Carbamazepine, Valproic acid, Omeprazole, Selective serotonin reuptake inhibitors, Morphine, the drug commonly known as ecstasy, Vincristine, and Amitriptyline.

Risk Factors and Frequency for Neurohypophysis

Neurohypophysis disorders can occur at any age, from childhood to late adulthood, and their causes can vary widely. This influences how common these disorders are. On average, 29 to 45 out of every 100,000 people have hypopituitarism, with 4.2 new cases per 100,000 people every year. These disorders affect both men and women equally. Most studies on this topic focus on problems with the whole pituitary gland.

In central DI, a disorder that often happens after a traumatic brain injury (TBI), the incidence ranges from 3 to 50%. The exact number can be hard to determine because the criteria used to diagnose DI can vary from study to study, potentially leading to an underestimate. About 15% of patients in hospitals have hyponatremia, which is when your blood doesn’t have enough sodium. This can be caused by SIADH, a condition where your body makes too much of a certain hormone. In fact, SIADH is the most common cause of hyponatremia after a TBI in both children and adults. It’s responsible for 46% of all hyponatremia cases and is the most common electrolyte problem. For some nerve disorders, over 70% of people will have SIADH. In neurological surgery units, 5 to 10% of patients have SIADH due to a problem with the part of the brain that regulates things like water balance in the body (the posterior neurohypophysis).

The neurohypophysis is a part of the brain where germinomas, a type of tumor, often occur. These tumors are most commonly found in the pineal region of the brain, and in half of cases with tumors in both the pineal and pituitary glands, the tumor is a germinoma.

Pituitary stalk interruption syndrome is a disorder that includes three key symptoms: an ectopic posterior pituitary, a thin or absent pituitary stalk, and an underdeveloped anterior pituitary. Central DI occurs in up to 10% of these cases and occurs more often in males. For people with hypopituitarism, this syndrome is the cause in 4-8% of cases.

Granular cell tumors are the most common type of tumor that starts in the neurohypophysis. They have been found in 9% of routine autopsies of the neurohypophysis. These tumors are unique to the neurohypophysis and the pituitary stalk and are thought to come from pituicytes. They occur twice as often in women than in men. These tumors make up 0.17% of all the tumors removed from the sellar region in a surgery called a transsphenoidal resection.

Sheehan syndrome is more common in developing countries and affects around 3.1% of women who have given birth, especially those who did so at home. This syndrome causes 6-8% of all cases of hypopituitarism.

Signs and Symptoms of Neurohypophysis

When diagnosing the medical condition known as Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH), doctors need to know about prior medical history and medication use. This is because certain illnesses and drugs, including antidepressants, seizure medication, antipsychotics, and cancer treatments, can cause SIADH secretion. The typical symptoms of SIADH include low sodium levels in the blood and normal fluid levels in the body. Some people may have normal blood pressure, heart rate, and skin moisture, no swelling from fluid buildup in their tissues, and regular central venous pressure if measured. As the low sodium levels worsen, people may experience nausea, vomiting, restlessness, headaches, exhaustion, an altered state of consciousness, seizures, coma, and even respiratory arrest.

Another condition related to the functioning of the neurohypophysis, or the posterior part of the pituitary gland, is Diabetes Insipidus (DI). When diagnosing DI, it’s crucial to rule out other potential causes as they will determine the course of treatment. Typical symptoms of DI include excessive urination and thirst. In the beginning, drinking more water can help balance the body’s fluid levels. In some scenarios, if the person doesn’t sense thirst and fails to drink enough water, they can develop a severe water deficiency. This can cause high sodium levels in the blood, signs of dehydration, and potentially lead to a brain issue causing irritability, confusion, disorientation, muscle twitching, seizures, coma, and even death. Some people may also feel weak, tired, and muscle pains.

In severe cases, DI can lead to acute kidney failure, low blood pressure, damage to the muscles, liver failure, and an increased risk of brain hemorrhage, stroke, and deep vein thrombosis in conditions with high levels of bodily fluids. A unique condition called Adipsic DI can occur when there’s damage to the part of the brain where the thirst mechanism is regulated, leading to the patient not feeling thirsty despite being dehydrated.

Testing for Neurohypophysis

The neurohypophysis is a part of your brain that can sometimes encounter disorders, most often linked with how the antidiuretic hormone (ADH) functions. ADH is responsible for absorbing water into your body and indirectly controlling the amount of salt your body releases. An issue with ADH can lead to problems with your body’s salt levels.

Brain magnetic resonance imaging (MRI) tests are the best way to study the functioning of the anterior and posterior pituitary, which includes the neurohypophysis. These tests can help doctors identify or rule out possible causes of neurohypophysis dysfunction.

Diabetic Insipidus is a condition that can occur due to neurohypophysis issues. Various tests such as checking salt levels in blood and urine, monitoring the amount of urine produced in a day or an hour, and examining the density of the urine can help in diagnosing this condition. A water deprivation test, sometimes combined with a medicine called desmopressin, can also be useful. In central diabetic insipidus, this medicine usually corrects the concentration of urine. However, in nephrogenic diabetic insipidus, the medicine’s effect is less noticeable.

When considering a condition called SIADH secretion, doctors first look at the body’s fluid levels. Next, they conduct tests that measure sodium in blood and urine, sugar and potassium levels in the blood, and check the liver’s functionality. Additional tests for thyroid-stimulating hormone (TSH), thyroxine (T4), and cortisol may be ordered to ensure that these are not causing any problems. The most common symptom of SIADH secretion is having low sodium levels in the blood while maintaining normal fluid levels. Other potential causes for low sodium must be ruled out in such cases.

Treatment Options for Neurohypophysis

In cases of central diabetes insipidus (commonly referred to as DI), an excess of urination and an extreme thirst, desmopressin is typically recommended as medication. This is administered either through the nose, orally, or via an injection. It’s crucial to find a suitable dosage that helps to reduce the symptoms without negatively affecting the electrolyte levels in the body.

In the event of acute DI following physical trauma, such as a traumatic brain injury (TBI), it’s important to assess whether the patient is conscious or not. If the patient is conscious, they should be encouraged to drink water. However, if they can’t drink, they need to receive fluids through a nasogastric tube, which is guided by daily weight checks. For unconscious patients, they are given a solution of 5% dextrose intravenously.

The goal of the treatment plan is to balance the electrolytes and have a normal urine output. It’s also essential to continually monitor sodium levels after administering desmopressin. In cases where the patient’s blood sodium level is too high (a condition known as hypernatremia), it’s critical to adjust the body’s sodium concentration gradually. This is often achieved by using a dextrose solution or water through a nasogastric tube.

For patients suffering from Syndrome of Inappropriate Antidiuretic Hormone (SIADH) secretion, a condition where the body retains too much water, the main treatment is restricting fluid intake to between 500-800 ml per day. If low sodium levels in the blood (a condition termed hyponatremia) persist, patients are usually given salt tablets and a type of diuretic medication called furosemide. The administration of isotonic fluids (fluids with balanced electrolyte concentration) won’t correct the deficit, but a 3% hypertonic solution can be given in severe cases of high sodium levels. In TBI, hypertonic saline can also reduce brain pressure.

The ideal correction rate of sodium concentration in the body should be no more than 0.5 to 1 milliequivalent per liter per hour, to avoid a dangerous condition called osmotic demyelination syndrome. For persistent hyponatremia, medications like tolvaptan or conivaptan can be given; both of these are vasopressin V2 receptor antagonists.

However, tolvaptan can be toxic to the liver, and should not be given to patients with liver disease. Alternatively, Demeclocycline, a type of tetracycline that inhibits vasopressin, can be administered, but it can also introduce side effects like reversible kidney insufficiency, liver cirrhosis, and sensitivity to sunlight. Urea has also been used to reduce the sodium excretion from the body and has shown comparable effects to vaptans in reversing hyponatremia in SIADH secretion.

There are numerous conditions that can cause altered body fluid levels. These can give rise to symptoms such as excessive thirst, water overload, or dehydration. Some of these conditions include:

Polydipsia (excessive thirst)
Water intoxication (drinking too much water)
Hypovolemia (low blood volume)
Nephrogenic Diabetes Insipidus (a kidney disorder)
Congestive heart failure
Cirrhosis (liver disease)
Uncontrolled diabetes mellitus
Continuous nausea/vomiting
Cerebral salt-wasting syndrome (a condition where the body loses too much sodium)
SIADH secretion (Syndrome of Inappropriate Antidiuretic Hormone)
Inappropriate intravenous therapy (wrong use of IV fluids)
Glucocorticoid deficiency (shortage of certain types of hormones)
Hypothyroidism (underactive thyroid)
Pseudohyponatremia (abnormally low sodium level in the blood)
Drugs that affect ADH (anti-diuretic hormone) such as carbamazepine, oxcarbazepine, chlorpropamide, cyclophosphamide, and selective serotonin reuptake inhibitors
Small cell lung cancer
Non-pulmonary tumors secreting ADH-like substances
High calcium level in the blood (Hypercalcemia)
Low potassium level in the blood (Hypokalemia)
Histiocytosis (an immune system disorder)

Each of these conditions requires a different treatment approach, so it’s essential for medical professionals to accurately identify the cause of the patient’s symptoms.

What to expect with Neurohypophysis

When the main cause of a condition called Diabetes Insipidus (DI) – an issue in which your body cannot balance its water levels – is properly treated, the outlook for recovery is excellent. However, an excessively high level of sodium in the blood (known as hypernatremia), can cause dangerous pressure in the brain, potentially leading to a condition called cerebral herniation – where the brain is squeezed out of its usual place.

In cases where DI is identified in trauma patients, most get better in 2 to 4 days, with the rest fully recovering within a 6-month period. This typically results in good outcomes for the patients. However, only a small percentage (6%) continue to have DI after a Traumatic Brain Injury (TBI). It’s worth noting that if DI develops soon after a TBI, it can increase the chances of the patient dying.

As for a condition known as Syndrome of Inappropriate Antidiuretic Hormone (SIADH) – a condition where the body produces too much antidiuretic hormone leading to low sodium levels in the body – the prognosis depends on the severity of the accompanying low sodium condition (hyponatremia) and how effective the treatment is. Hyponatremia can significantly contribute to serious illness and even death. Managing SIADH can be complicated and simply reducing water intake may not be enough to correct hyponatremia, which means further investigations and alternative treatments may be required.

Possible Complications When Diagnosed with Neurohypophysis

Possible complications to be aware of include:

Hyponatremia (low sodium levels in the blood)
Hypernatremia (high sodium levels in the blood)
Confusion
Seizures
Muscle twitching
Lethargy (extreme tiredness)
Coma
Death
Lack of breastfeeding
Poor contraction of the uterus
Difficulty with cervix dilatation
Reduced sexual response
Depression

Preventing Neurohypophysis

Treating a patient with disorders linked to the neurohypophysis (part of the brain responsible for releasing certain hormones) within a hospital can be tricky. If not acted on quickly, some complications can develop. The symptoms can be very diverse, especially those linked to abnormal levels of sodium in the body. These can worsen to the point of causing unconsciousness or even death if left untreated.

As a patient, it’s important to observe any changes in the amount of urine you pass or an increase in feeling thirsty. Watch out for symptoms like frequent urination, excessive thirst, muscle weakness, twitching, or feeling confused. If you notice any of these, it’s crucial to reach out to your doctor immediately for further check-up and care.