Maternal complications of pregnancy may include mirror syndrome. Maternal complications of delivery may include a Cesarean section or, alternatively, a vaginal delivery with mechanical dystocia.

Complications of the mass effect of a teratoma in general are addressed on the teratoma page. Complications of the mass effect of a large SCT may include hip dysplasia, bowel obstruction, urinary obstruction, hydronephrosis and hydrops fetalis. Even a small SCT can produce complications of mass effect, if it is presacral (Altman Type IV). In the fetus, severe hydronephrosis may contribute to inadequate lung development. Also in the fetus and newborn, the anus may be imperforate.

Later complications of the mass effect and/or surgery may include neurogenic bladder, other forms of urinary incontinence, fecal incontinence, and other chronic problems resulting from accidental damage to or sacrifice of nerves and muscles within the pelvis. Removal of the coccyx may include additional complications. In one review of 25 patients, however, the most frequent complication was an unsatisfactory appearance of the surgical scar.

SCTs are very rare in adults, and as a rule these tumors are benign and have extremely low potential for malignancy. This estimation of potential is based on the idea that because the tumor existed for decades prior to diagnosis, without becoming malignant, it has little or no potential to ever become malignant. For this reason, and because coccygectomy in adults has greater risks than in babies, some surgeons prefer not to remove the coccyx of adult survivors of SCT. There are case reports of good outcomes.

These lesions usually present in neonates, although they may not come to clinical attention until adulthood (for cosmetic reasons). There is no gender predilection. They are present in approximately 3-6 per 1000 live births.

Nasal glial heterotopia is rare, while an encephalocele is uncommon. NGH usually presents in infancy, while encephalocele may present in older children and adults. It is seen in both genders equally.

Embryonal teratomas most commonly occur in the sacrococcygeal region: sacrococcygeal teratoma is the single most common tumor found in newly born humans.

Of teratomas on the skull sutures, approximately 50% are found in or adjacent to the orbit. Limbal dermoid is a choristoma, not a teratoma.

Teratoma qualifies as a rare disease, but is not extremely rare. Sacrococcygeal teratoma alone is diagnosed at birth in one out of 40,000 humans. Given the current human population and birth-rate, this equals five per day or 1800 per year. Add to that number sacrococcygeal teratomas diagnosed later in life, and teratomas in other locales, and the incidence approaches ten thousand new diagnoses of teratoma per year.

Cysts derived from CNS tissues are very common in America. They are a subtype of cerebrovascular diseases, which are the third leading cause of death in America. Generally, CNS cysts are present in all geographic regions, races, ages, and sexes. However, certain types of CNS cysts are more prevalent in certain types of individuals than others. Some examples of incidence rates in specific types of cysts include:

- Arachnoid cysts are more prevalent in males than females

- Colloid cysts are more prevalent in adults

- Dermoid cysts are more prevalent in children under 10 years of age

- Epidermoid cysts are more prevalent in middle-aged adults

Large and especially giant congenital nevi are at higher risk for malignancy degeneration into melanoma. Because of the premalignant potential, it is an acceptable clinical practice to remove congenital nevi electively in all patients and relieve the nevocytic overload.

Many CNS cysts form in the womb during the first few weeks of development as a result of congenital defects. In adults cysts may also form due to a head injury or trauma, resulting in necrotic tissues (dead tissue), and can sometimes be associated with cancerous tumors or infection in the brain. However, the underlying reasons for cyst formation are still unknown.

Although often described as benign, a teratoma does have malignant potential. In a UK study of 351 infants and children diagnosed with "benign" teratoma reported 227 with MT, 124 with IT. Five years after surgery, event-free survival was 92.2% and 85.9%, respectively, and overall survival was 99% and 95.1%. A similar study in Italy reported on 183 infants and children diagnosed with teratoma. At 10 years after surgery, event free and overall survival were 90.4% and 98%, respectively.

Depending on which tissue(s) it contains, a teratoma may secrete a variety of chemicals with systemic effects. Some teratomas secrete the "pregnancy hormone" human chorionic gonadotropin (βhCG), which can be used in clinical practice to monitor the successful treatment or relapse in patients with a known HCG-secreting teratoma. This hormone is not recommended as a diagnostic marker, because most teratomas do not secrete it. Some teratomas secrete thyroxine, in some cases to such a degree that it can lead to clinical hyperthyroidism in the patient. Of special concern is the secretion of alpha-fetoprotein (AFP); under some circumstances AFP can be used as a diagnostic marker specific for the presence of yolk sac cells within the teratoma. These cells can develop into a frankly malignant tumor known as yolk sac tumor or endodermal sinus tumor.

Adequate follow-up requires close observation, involving repeated physical examination, scanning (ultrasound, MRI, or CT), and measurement of AFP and/or βhCG.

Polyembryoma is a rare, very aggressive form of germ cell tumor usually found in the ovaries. Polyembryoma has features of both yolk sac tumour and undifferentiated teratoma/embryonal carcinoma, with a characteristic finding of embryoid bodies lying in a loose mesenchymal stroma.

It has been found in association with Klinefelter syndrome.

Treatment for dermoid cyst is complete surgical removal, preferably in one piece and without any spillage of cyst contents. Marsupialization, a surgical technique often used to treat pilonidal cyst, is inappropriate for dermoid cyst due to the risk of malignancy.

The association of dermoid cysts with pregnancy has been increasingly reported. They usually present the dilemma of weighing the risks of surgery and anesthesia versus the risks of untreated adnexal mass. Most references state that it is more feasible to treat bilateral dermoid cysts of the ovaries discovered during pregnancy if they grow beyond 6 cm in diameter.

The disorder is an autosomal dominant genetic trait caused by a mutation in the HLXB9 homeobox gene. In 2000 the first large series of Currarino cases was genetically screened for HLXB9 mutations, and it was shown that the gene is specifically causative for the syndrome, but not for other forms of sacral agenesis. The study was published on the American Journal of Human Genetics.

A dermoid cyst is a teratoma of a cystic nature that contains an array of developmentally mature, solid tissues. It frequently consists of skin, hair follicles, and sweat glands, while other commonly found components include clumps of long hair, pockets of sebum, blood, fat, bone, nails, teeth, eyes, cartilage, and thyroid tissue.

As dermoid cysts grow slowly and contain mature tissue, this type of cystic teratoma is nearly always benign. In those rare cases wherein the dermoid cyst is malignant, a squamous cell carcinoma usually develops in adults, while infants and children usually present with an endodermal sinus tumor.

The Currarino syndrome (also Currarino triad) is an inherited congenital disorder where either the sacrum (the fused vertebrae forming the back of the pelvis) is not formed properly, or there is a mass in the presacral space in front of the sacrum, and (3) there are malformations of the anus or rectum. It can also cause an anterior meningocele or a presacral teratoma.

Presacral teratoma usually is considered to be a variant of sacrococcygeal teratoma. However, the presacral teratoma that is characteristic of the Currarino syndrome may be a distinct kind.

Nasal glial heterotopia refers to congenital malformations of displaced normal, mature glial tissue, which are no longer in continuity with an intracranial component. This is distinctly different from an encephalocele, which is a herniation of brain tissue and/or leptomeninges, that develops through a defect in the skull, where there is a continuity with the cranial cavity.

Pineocytoma, also known as a pinealocytoma, is a benign, slowly growing tumor of the pineal gland. Unlike the similar condition pineal gland cyst, it is uncommon.

A struma ovarii (literally: goitre of the ovary) is a rare form of monodermal teratoma that contains mostly thyroid tissue, which may cause hyperthyroidism.

Despite its name, struma ovarii is not restricted to the ovary.

The vast majority of struma ovarii are benign tumors; however, malignant tumors of this type is found in a small percentage of cases.

Simple surgical excision is curative. The recommended treatment is that the skin is peeled off the extra-auricular tissue and protruding cartilage remnants are trimmed. Normal appearance is achieved in majority of cases. The reconstruction successful in true cases of accessory auricle, as it also is in individuals with auricular appendages.

One proposed cause of pilonidal cysts is ingrown hair. Excessive sitting is thought to predispose people to the condition, as sitting increases pressure on the coccygeal region. Trauma is not believed to cause a pilonidal cyst; however, such an event may result in inflammation of an existing cyst. However, there are cases where this can occur months after a localized injury to the area. Some researchers have proposed that pilonidal cysts may be the result of a congenital pilonidal dimple. Excessive sweating can also contribute to the cause of a pilonidal cyst. Moisture can fill a stretched hair follicle, which helps create a low-oxygen environment that promotes the growth of anaerobic bacteria, often found in pilonidal cysts. The presence of bacteria and low oxygen levels hamper wound healing and exacerbate a forming pilonidal cyst.

Large congenital nevi are caused by a mutation in the body's cells that occurs early in embryonic development, usually within the first twelve weeks of pregnancy. Mutations are sometimes found in genes that code for NRAS and KRAS proteins. There is no known method of prevention.

A pineal gland cyst is a usually benign (non-malignant) cyst in the pineal gland, a small endocrine gland in the brain. Historically, these fluid-filled bodies appeared on of magnetic resonance imaging (MRI) brain scans, but were more frequent at death, seen in of autopsies. A 2007 study by Pu "et al". found a frequency of 23% in brain scans (with a mean diameter of 4.3 mm).

It was once believed that smaller cysts (less than 5.0 mm) were usually asymptomatic, but for larger cysts (greater than 5.0 mm), symptoms could include headache, unexpected seizures, visual disturbances, memory loss, cognitive decline, muscle fasciculations, nausea, weakness, fatigue, light sensitivity, tinnitus, circadian rhythm dysfunction, or hydrocephalus if the cyst impinged on the superior colliculi or caused obstruction of the cerebral aqueduct. Newer research shows that the size of the cyst does not necessarily correlate to the presence of symptoms. In some cases, it will need to be removed before life-threatening situations occur.

Despite the pineal gland being in the center of the brain, due to recent advancements in endoscopic medicine, endoscopic brain surgery to drain and/or remove the cyst can be done with the patient spending 1-3 nights in the hospital, and being fully recovered in weeks, rather than a year, as is the case with open-skull brain surgery.

The National Organization for Rare Disorders states that pineal cysts larger than 5.0 mm are "rare findings" and are possibly symptomatic. If narrowing of the cerebral aqueduct occurs, many neurological symptoms may exist, including headaches, vertigo, nausea, muscle fasciculations, eye sensitivity, and ataxia. Continued monitoring of the cyst might be recommended to monitor its growth, and surgery may be necessary.

In a small population of people with larger, symptomatic cysts, the following comorbid conditions have been noted: Pseudotumor cerebri (elevated intracranial pressure), empy sella, hormonal disturbances, flattened optic discs, chiari malformation, sjogren's, POTS, dysautonomia, PCOS.

An immature teratoma is a rare type of malignant (cancerous) germ cell tumor (type of tumor that begins in the cells that give rise to sperm or eggs).

Like a mature teratoma, it contains several different types of tissue such as hair, muscle, and bone. Unlike a mature teratoma, it contains primitive neuroepithelium.

In medicine, heterotopia is the presence of a particular tissue type at a non-physiological site, but usually co-existing with original tissue in its correct anatomical location. In other words, it implies ectopic tissue, in addition to retention of the original tissue type. In neuropathology, for example, gray matter heterotopia is the presence of gray matter within the cerebral white matter or ventricles. Heterotopia within the brain is often divided into three groups: subependymal heterotopia, focal cortical heterotopia and band heterotopia. Another example is a Meckel's diverticulum, which may contain heterotopic gastric or pancreatic tissue.

In biology specifically, "heterotopy" refers to an altered location of trait expression. In her book "Developmental Plasticity and Evolution", Mary-Jane West Eberhard has a cover art of the sulphur crested cockatoo and comments on the back cover "Did long crest[head] feathers evolve by gradual modification of ancestral head feathers? Or are they descendants of wing feathers, developmentally transplanted onto the head". This idea sets the tone for the rest of her book which goes into depth about developmental novelties and their relation to evolution. Heterotopy is a somewhat obscure but well demonstrated example of how developmental change can lead to novel forms. The central concept is that a feature seen in one area of an organism has had its location changed in evolutionary lineages.

Ectomesenchymoma is a rare, fast-growing tumor of the nervous system or soft tissue that occurs mainly in children, although cases have been reported in patients up to age 60. Ectomesenchymomas may form in the head and neck, abdomen, perineum, scrotum, or limbs. Also called malignant ectomesenchymoma.

Malignant ectomesenchymoma (MEM) is a rare tumor of soft tissues or the CNS, which is composed of both neuroectodermal elements [represented by ganglion cells and/or well-differentiated or poorly differentiated neuroblastic cells such as ganglioneuroma, ganglioneuroblastoma, neuroblastoma, peripheral primitive neuroectodermal tumors – PNET] and one or more mesenchymal neoplastic elements, usually rhabdomyosarcoma . The most accepted theory suggests that this tumor arises from remnants of migratory neural crest cells and thus from the ectomesenchyme.

A pilonidal cyst can resemble a dermoid cyst, a kind of teratoma (germ cell tumor). In particular, a pilonidal cyst in the gluteal cleft can resemble a sacrococcygeal teratoma. Correct diagnosis is important because all teratomas require complete surgical excision, if possible without any spillage, and consultation with an oncologist.