With so few individuals actually surviving until birth, the only treatment option is surgery to try to remove the parasitic twin. Surgery, however, is very dangerous and has been successful only once. The problem with surgical intervention is that the arterial supplies of the head are so intertwined that it is very hard to control the bleeding, and it has been suggested that cutting off the parasitic twin's arterial supply might improve the odds of the developed twin's survival.

In the past, the use of terminology when describing parasitic twins has been somewhat inconsistent. By definition, a parasitic twin is joined to another twin in a certain anatomical location or position on the developed twin's body. The underdeveloped twin is termed the parasite, and the developed twin is termed the autosite. The autosite can have some abnormalities, as well. For the most part, however, it has developed enough that it can live on its own.

Craniopagus twins are conjoined twins that are fused at the cranium. This condition occurs in about 10–20 babies in every million births in the United States. Among this small group, cephalic conjoining, or craniopagus twinning, represents the rarest of congenital abnormalities, accounting for 2–6% of all conjoined twins. Additionally, conjoined twins are genetically identical and always share the same sex. The union in craniopagus twins may occur on any portion of the Calvary, but does not include either the face or the foramen magnum. The thorax and abdomen are separate and each twin has its own umbilicus and umbilical cord. The union may involve the entire diameter of the head or only a small portion. This suggests that although there are many different kinds of vulnerabilities already known in the scientific community, there are an infinite number of variations that can occur. Most of these variations are based on the rotation of one twin's skull to the other and the different phenotype sub-groups of craniopagus twins are based on all these rotational conformations. Each of these factors (rotation, spot of union) affects the development of the brain, the vascular system within the brain and overall wellness of life both of the twins have outside the womb. Relatively few craniopagus twins survive the perinatal period – approximately 40% of conjoined twins are stillborn and an additional 33% die within the immediate perinatal period, usually from organ abnormalities and failure. However 25% of craniopagus twins survive and can be considered for a surgical separation and several attempts occur yearly worldwide. In the last-half century, many advances in medicine including brain imaging, neuro-anesthesia and neurosurgical techniques have proven that a successful outcome is possible following separation of total craniopagus twins.

"'Conjoined twins" are identical twins joined in utero. An extremely rare phenomenon, the occurrence is estimated to range from 1 in 49,000 births to 1 in 189,000 births, with a somewhat higher incidence in Southeast Asia and Africa. Approximately half are stillborn, and an additional one-third die within 24 hours. Most live births are female, with a ratio of 3:1.

Two contradicting theories exist to explain the origins of conjoined twins. The more generally accepted theory is "fission", in which the fertilized egg splits partially. The other theory, no longer believed to be the basis of conjoined twinning, is fusion, in which a fertilized egg completely separates, but stem cells (which search for similar cells) find like-stem cells on the other twin and fuse the twins together. Conjoined twins share a single common chorion, placenta, and amniotic sac, although these characteristics are not exclusive to conjoined twins as there are some monozygotic but non-conjoined twins who also share these structures in utero.

The most famous pair of conjoined twins was Chang and Eng Bunker (Thai: อิน-จัน, In-Chan) (1811–1874), Thai brothers born in Siam, now Thailand. They traveled with P.T. Barnum's circus for many years and were labeled as the Siamese twins. Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins.

Surgery to separate conjoined twins may range from very easy to very difficult depending on the point of attachment and the internal parts that are shared. Most cases of separation are extremely risky and life-threatening. In many cases, the surgery results in the death of one or both of the twins, particularly if they are joined at the head or share a vital organ. This makes the ethics of surgical separation, where the twins can survive if not separated, contentious. Alice Dreger of Northwestern University found the quality of life of twins who remain conjoined to be higher than is commonly supposed. Lori and George Schappell and Abby and Brittany Hensel are notable examples.

In 1955, neurosurgeon Harold Voris (1902-1980) and his team at Mercy Hospital in Chicago performed the first successful operation to separate Siamese twins conjoined (Craniopagus twins) at the head, which resulted in long-term survival for both. The larger girl was reported in 1963 as developing normally, but the smaller was permanently impaired.

In 1957, Bertram Katz and his surgical team made international medical history performing the world's first successful separation of conjoined twins sharing a vital organ. Omphalopagus twins John Nelson and James Edward Freeman (Johnny and Jimmy) were born to Mr. and Mrs. William Freeman of Youngstown, Ohio, on April 27, 1956. The boys shared a liver but had separate hearts and were successfully separated at North Side Hospital in Youngstown, Ohio by Bertram Katz. The operation was funded by the Ohio Crippled Children's Service Society.

Recent successful separations of conjoined twins include that of the separation of Ganga & Jamuna Shreshta in 2001, who were born in Kathmandu, Nepal, in 2000. The 197-hour surgery on the pair of craniopagus twins was a landmark one which took place in Singapore; the team was led by neurosurgeons Chumpon Chan and Keith Goh. The surgery left Ganga with brain damage and Jamuna unable to walk. Seven years later, Ganga Shrestha died at the Model Hospital in Kathmandu in July 2009, at the age of 8, three days after being admitted for treatment of a severe chest infection.

A case of particular interest was that of infants Rose and Grace ("Mary" and "Jodie") Attard, conjoined twins from Malta who were separated in Great Britain by court order over the religious objections of their parents, Michaelangelo and Rina Attard. The surgery took place in November, 2000, at St Mary's Hospital in Manchester. The operation was controversial because Rose, the weaker twin, would die as a result of the procedure as her heart and lungs were dependent upon Grace's. (The twins were attached at the lower abdomen and spine.) However, if the operation had not taken place, it was certain that both twins would die. Grace survived to enjoy a normal childhood.

In 2003 two 29-year-old women from Iran, Ladan and Laleh Bijani, who were joined at the head but had separate brains (craniopagus) were surgically separated in Singapore, despite surgeons' warnings that the operation could be fatal to one or both. Their complex case was accepted only because high tech graphical imagery and modelling would allow the medical team to plan the risky surgery. Unfortunately, an undetected major vein hidden from the scans was discovered during the operation. The separation was completed but both women died while still in surgery on July 8, 2003.

Two-headed people and animals, though rare, have long been known to exist and documented.

There are two categories of craniopagus twins:

- Partial Although partial craniopagus is less common than total, it is still a division of craniopagus twins that is worth exploring. This type of twinning is defined as having limited surface area involvement, with either intact crania or cranial defects. In other words, it is a defect of the cranial "coverings." In partial craniopagus twins, the unions are usually frontal and less commonly occipital and vertical. Angular frontal junctions occur when the two twins are joined at any part of the forehead. Occipital twins are joined at the occipital lobe in the back of the head and vertical are joined on the top of the head and usually face opposite directions. The junctional diameter is often smaller in partial forms and occasionally an incomplete layer of bone may be present between the twins. Each child maintains independent calvarial convexities except at the common area of skull junction. The dura of both children may be intact or deficient and cortical gyri may interdigitate. Additionally shared dural venous sinuses is usually absent or if it is present it is negligible. These twins usually undergo successful separation and both twins may live to lead normal lives.

- Total Total craniopagus twins are defined as sharing extensive surface area with widely connected cranial cavities. Among total craniopagus twins, there are four main categories which are then further divided into several subcategories. Frontal, the first category, are when twins are facing each other with the axis of the bodies forming an acute angle. Temporoparietal craniopagi are joined immediately above the external auditory meatus. The third division is the occipital anomaly where the twins are connected in the occipital lobe causing the twins to face away from each other. The final variant is the parietal craniopagus which occurs when twins fuse at the vertex with the axis of the twins forming an obtuse angle. This category is perhaps the most important, or most interesting because the craniums of the two twins share the most veins, lobes and circuitry and is often described as one brain shared by two individuals.

- "Type 1": both children face in the same general directional axis so that the angle between twins is less than 40 degrees. These twins show relatively symmetric superior bi-parietal or vertex compressional flattening.

- "Type 2": both children face opposite directions so that the deformity shows an axial rotation between 140-180 degrees.

- "Type 3": in this variety axial rotation is intermediate between the first two types with a rotation of being between 40 and 140.

In humans, as in other animals, partial twinning can result in formation of two heads supported by a single torso. Two ways this can happen are dicephalus parapagus, where there are two heads side by side, and craniopagus parasiticus, where the heads are joined directly.

Anastasia and Tatiana Dogaru

born August 29, 2004) are craniopagus conjoined twins. They were scheduled to begin the first of several surgeries to separate them at Rainbow Babies and Children's Medical Center in Cleveland, Ohio. However, in August 2007 the surgery was called off as too dangerous.

The twins were born in Rome, Italy to Romanian parents, Alin Dogaru, a Byzantine Catholic priest, and Claudia Dogaru, a nurse. Their mother heard about the successful separation of Egyptian-born twins who were also joined at the head and hoped her children could also be successfully separated. The Dogaru family — who also have an older daughter, Maria, and younger son Theodor — were brought to north Texas by the World Craniofacial Foundation to have Anastasia and Tatiana evaluated for possible separation.

The girls are currently developing normally for their age and speak both Romanian and English. They get around with Anastasia leading the way and Tatiana following. The top of Tatiana's head is attached to the back of Anastasia's. Anastasia, whose kidneys don't function, relies on her sister's kidneys, and Tatiana on her sister's circulatory system. The girls also share blood flow to the back of the brain and some brain matter. Doctors estimated the twins had only a 50 percent chance of surviving the surgery. There were also risks of complications, such as brain damage, but the girls also risk early death if they remain conjoined. Their parents believed separation would give them their best chance at living a normal life.

In May 2007, doctors used a catheter to insert wire coils into the veins of the two girls, successfully redirecting their blood flow. It was the first time the procedure was attempted in conjoined twins. Doctors pushed back the first of the planned separation surgeries to June 2007 while studying the complex circulatory system of the twins, but, in August of that year, decided it was too risky.

Krista and Tatiana Hogan (born October 25, 2006) are Canadians who are conjoined craniopagus twins. They are joined at the head (the top, back, and sides). They were born in Vancouver, British Columbia and are the only unseparated ones of that type currently alive in Canada. They live with their mother, Felicia Simms, in Vernon, British Columbia and often travel to Vancouver for care at BC Children's Hospital and Sunny Hill Health Centre for Children.

Clarence and Carl Aguirre (born April 21, 2002) are former conjoined twins born in Silay City, Philippines. They were conjoined at the top of the head (vertical craniopagus). In 2003 they were brought to the United States by their mother Arlene in the hope of having them surgically separated. A revolutionary new process was used in separating the twin boys. Because "marathon" surgical operations have historically led to a high rate of mortality and morbidity, Clarence and Carl's doctors chose to separate them in several smaller operations, allowing the twins to recuperate after each surgery.

In October 2003, tissue expanders (pouches filled with saline) were implanted under the boys' scalps. This is common practice in separating conjoined twins, as it creates more skin that can be used to cover the twins' wounds after separation. Over the next ten months, the brothers underwent several more operations to tease apart their joined skulls and brains. On August 4, 2004, the final surgery was completed. All of these operations were performed at Montefiore Medical Center in the Bronx, New York by a team led by Dr. James T. Goodrich, a pediatric neurosurgeon and Dr. David A. Staffenberg, a plastic surgeon. They received most of their post-operative rehabilitation at Blythedale Children's Hospital in Valhalla, New York (Westchester County).

By December 2005, Clarence could walk short distances unassisted, and Carl could walk with a walker. As of August 2014 both boys and their mother live in a donated house in Scarsdale, New York. The twins continue to attend physical therapy at Blythedale. Goodrich says there was some degeneration of Carl’s right parietal lobe: he takes medication to control seizures, can utter just a word or two at a time, and has limited use of his left arm and leg. Both must still wear helmets to protect their brains; when they are fully grown, their skulls will be patched.

Based on statistics, the twins were given a 20% chance of survival at birth . At birth at B.C. Women's Hospital & Health Centre, they were described as "wriggly, vigorous and very vocal." They weighed twelve and a half pounds, not six and a half pounds as reported by some media outlets, when they were born by caesarean section.

Lori and George Schappell (born as Lori and Dori Schappell, September 18, 1961, in Sinking Spring, Pennsylvania) are conjoined twins. George has performed as a country singer. In 2007, George, who was at that time known as Reba Schappell, stated that although born female, he identifies as male and changed his name to George.

Globally, infants are a population that are especially vulnerable to foodborne disease. The World Health Organization has issued recommendations for the preparation, use and storage of prepared formulas. Breastfeeding remains the best preventative measure for protection of foodborne infections in infants.

Food may be contaminated during all stages of food production and retailing. In order to prevent viral contamination, regulatory authorities in Europe have enacted several measures:

- European Commission Regulation (EC) No 2073/2005 of November 15, 2005

- European Committee for Standardization (CEN): Standard method for the detection of norovirus and hepatitis A virus in food products (shellfish, fruits and vegetables, surfaces and bottled water)

- CODEX Committee on Food Hygiene (CCFH): Guideline for the application of general principles of food hygiene for the control of viruses in food

Many imaging modalities are used to aid in the diagnosis of primary liver cancer. For HCC these include sonography (ultrasound), computed tomography (CT) and magnetic resonance imaging (MRI). When imaging the liver with ultrasound, a mass greater than 2 cm has more than 95% chance of being HCC. The majority of cholangiocarcimas occur in the hilar region of the liver, and often present as bile duct obstruction. If the cause of obstruction is suspected to be malignant, endoscopic retrograde cholangiopancreatography (ERCP), ultrasound, CT, MRI and magnetic resonance cholangiopancreatography (MRCP) are used.

Tumor markers, chemicals sometimes found in the blood of people with cancer, can be helpful in diagnosing and monitoring the course of liver cancers. High levels of alpha-fetoprotein (AFP) in the blood can be found in many cases of HCC and intrahepatic cholangiocarcinoma. Cholangiocarcinoma can be detected with these commonly used tumor markers: carbohydrate antigen 19-9 (CA 19-9), carcinoembryonic antigen (CEA) and cancer antigen 125 (CA125). These tumour markers are found in primary liver cancers, as well as in other cancers and certain other disorders.

Prevention of cancers can be separated into primary, secondary, and tertiary prevention. Primary prevention preemptively reduces exposure to a risk factor for liver cancer. One of the most successful primary liver cancer preventions is vaccination against hepatitis B. Vaccination against the hepatitis C virus is currently unavailable. Other forms of primary prevention are aimed at limiting transmission of these viruses by promoting safe injection practices, screening blood donation products, and screening high-risk asymptomatic individuals. Aflatoxin exposure can be avoided by post-harvest intervention to discourage mold, which has been effective in west Africa. Reducing alcohol abuse, obesity, and diabetes would also reduce rates of liver cancer. Diet control in hemochromatosis could decrease the risk of iron overload, decreasing the risk of cancer.

Secondary prevention includes both cure of the agent involved in the formation of cancer (carcinogenesis) and the prevention of carcinogenesis if this is not possible. Cure of virus-infected individuals is not possible, but treatment with antiviral drugs such as interferon can decrease the risk of liver cancer. Chlorophyllin may have potential in reducing the effects of aflatoxin.

Tertiary prevention includes treatments to prevent the recurrence of liver cancer. These include the use of chemotherapy drugs and antiviral drugs.

Born as Lori and Dori Schappell, they are craniopagus conjoined twins joined at the head, but having very different personalities and living—insofar as possible—individual lives. As a mark of individuality, and disliking the fact that their names rhymed, Dori first chose to go by the name Reba, after his favorite singer Reba McEntire. By 2007 he preferred to be publicly known as George.

Lori and George spent the first 24 years of their lives living in an institution in Hamburg, Pennsylvania in which the majority of patients were suffering from severe intellectual disabilities. Although neither is intellectually disabled, George's physical condition required special care. A court decision was made that their parents would be unable to care for them properly and they were removed and institutionalized. In the 1960s there were few hospital institutions for people who had special needs that were particularly unusual. In order that they might be placed in the institution, they were diagnosed as suffering from intellectual disability. When they reached adulthood, George, with the help of Ginny Thornburgh, wife of former Pennsylvania Governor Richard Thornburgh, fought to have this diagnosis overturned and they were able to go to college.

While Lori is able-bodied, George has spina bifida, which has caused growth restriction of his lower body and severe mobility impairment. They are therefore of very different heights with her being 5' 1" and him 4'4". There was no wheelchair that suited his unique condition, because to move around, he must be raised to her height, to avoid undue strain upon his neck and back. The only thing on wheels that was the right height was a bar stool. Using this as the foundation, he designed the wheelchair that he currently uses.

Lori and George live in a two-bedroom apartment, each maintaining their own private space. He has several pets. She is a trophy-winning bowler. They respect each other’s privacy in terms of work time, recreation and relationships. She has had several boyfriends and was engaged, but lost her fiance in a motor-vehicle accident.

In 2006, George was baptized a member of the Church of Jesus Christ of Latter-day Saints, in Reading. Lori did not join, but has been supportive of his decision. In 2007, he decided to openly acknowledge that he was transgender, having self-identified as male from a young age.