What is Cavum Veli Interpositi?
The velum interpositum (VI) is a type of membrane found in the brain, made up of two layers from the tela choroidea of the third ventricle. This membrane creates a potential space filled with cerebrospinal fluid (CSF), located between the internal cerebral veins (ICV) and the posterior medial choroidal artery.
Back in 1930, Kruse defined the enlargement of this space as “cavum veli interpositi” (CVI). Other common terms for this structure include “ventriculi tertii,” “cisterna interventricularis,” “transverse fissure,” and “sub-trigonal fissure.” CVI tends to be triangular in shape, wide at the back and pointed at the front, extending as far as the opening known as the foramen of Monroe.
This brain structure has specific boundaries: at the top, it’s delimited by the fornix and the hippocampal commissure; at the bottom, by the tela choroidea of the third ventricle and the internal cerebral veins; on the sides, by the thalamus; at the front by the roof of the third ventricle and the interventricular foramina; and at the back by the splenium of the corpus callosum and the habenular commissure.
What Causes Cavum Veli Interpositi?
CVI, or Cystic Persistent Primitive Structures, are a part of a group of cyst-like structures within the brain. These structures also include the absence of the septum pellucidum (ASP), the cavum septi pellucidi (CSP), and the cavum vergae (CV). These structures are naturally present during the growth and development of the brain while a baby is still in the womb. Generally, these structures tend to fade away between the baby’s seventh month in the womb and its second year after birth. While these structures are normal to find during fetal life, they can still be found in some adults.
Interestingly, these spaces within the brain don’t have ependymal covering, which is a type of cellular layer in the brain. Additionally, they don’t have a lining of choroid plexus cells, another type of brain cell. They’re directly connected to the subarachnoid space, a space filled with fluid that’s between the brain and its protective covering. Because these spaces are separated from the ventricular system, or fluid-filled cavities in the brain, they’re not considered a part of that system.
CVI is an anatomical variation that emerges from a protrusion of the pia mater, which is one of the protective layers of the brain, into the early developing neural tube around the third month of fetal development.
Risk Factors and Frequency for Cavum Veli Interpositi
Cavum velum interpositum (CVI) is something normally found in the brains of unborn babies. Usually, the size of CVI decreases after birth and is rare in adults. Let’s go through a few statistics regarding this:
- CVI persists in about 30% of children aged between 1 and 10.
- Around 21% of preterm birth children showed the incidence of CVI based on an ultrasonography study.
- In a CT scan study of 442 adults, the incidence of CVI was about 7.24%.
- In a study of 505 neurosurgical patients ranging in age from 2 months to 79 years, 5.54% had CVI.
- There is no significant difference in the occurrence of CVI between different genders and age groups.
- CVI is considered to occur twice as often as the cavum vergae, another structure in the brain.
Signs and Symptoms of Cavum Veli Interpositi
There is ongoing research about the role of a brain structure called cavum veli interpositi (CVI) in brain diseases, but findings are still unclear. Some studies suggest that CVI could be linked to a condition where a person’s ventricles (fluid-filled spaces in the brain) enlarge moderately without increasing brain pressure, leading to a progressively larger head size.
In other research, the presence of an enlarged CVI in children has been suggested to potentially relate to the development of hydrocephalus (buildup of fluid in the brain), seizures, and mental delays.
In a study conducted by Tubbs and his team, they examined identical twins who had midline cerebral cysts (fluid-filled sacs in the brain), bigger head sizes, and mild enlargement of the brain’s ventricles. They proposed that these cysts could cause a small head size and slight ventricular enlargement due to recurring increases in brain pressure. These symptoms might intermittently occur due to a ball-valve mechanism between the cisterna CVI and another structure called the cisterna venae magnae Galeni.
Testing for Cavum Veli Interpositi
Chronic venous insufficiency (CVI) is often incidentally found during regular MRI or CT scans done for other health issues. It can also usually be seen during ultrasound scans of a newborn’s head.
Treatment Options for Cavum Veli Interpositi
The main way to treat small cysts in the cavum veli interpositi (a cavity in the brain) is to collapse them. For larger cysts that start causing symptoms, two proven methods are shunting or endoscopic ventricular fenestration. These techniques establish a connection between the space filled with cerebrospinal fluid in the middle of the brain and the area containing the ventricles. The ventriculoperitoneal shunting specifically creates a connection between the cyst and the ventricular system.
What else can Cavum Veli Interpositi be?
When checking for cysts in a particular area of the brain known as the cavum veli interpositi, doctors need to differentiate from several possibilities:
- Cavum septi pellucidi (CSP): This is a cyst that looks triangular and is in front of the foramen of Monro, located amidst the frontal horns of the brain cavities known as lateral ventricles.
- Cavum vergae: It is a cyst that looks like a rectangle and is situated right above pillars of the foramen, which are moved downwards.
- Pineal cyst: This cyst is commonly found in the same area, usually causing no symptoms. It’s located below a pair of major veins inside the brain and it’s near the brain’s bump-like features called colliculi.
- Arachnoid cyst: This cyst is often seen in the area of the quadrigeminal cistern and can resemble a cavum veli interpositi. It is mostly found below the cerebral veins and does not have a triangular shape.
Identifying the exact position and shape of these structures can assist doctors in making accurate diagnoses.
What to expect with Cavum Veli Interpositi
The Cavum veli interpositi is often discovered accidentally during an MRI or CT scan and usually doesn’t cause any symptoms. There are rare cases where it does cause symptoms and in these situations, it’s treated with the collapsing of the cavity, redirecting fluid, or making a small hole in the ventricle using an endoscope. These treatments have traditionally been successful.
Possible Complications When Diagnosed with Cavum Veli Interpositi
Studies have found a potential link between the presence of a bodily structure called the cavum veli interpositi (CVI) in children and the development of disorders related to psychosis. There are also suggestions that CVI may contribute to the development of water on the brain (hydrocephalus), mental disabilities, and seizures in children. However, it is important to note that these studies all agree that more research is needed to determine if there are any health issues directly linked to the presence of CVI.
Preventing Cavum Veli Interpositi
Patients should be made aware that the presence of cavum veli interpositi is a normal variation in body structure, not something to be concerned about. It typically doesn’t need surgery, except in very infrequent, exceptional situations.
