Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs.

Many additional body parts form by the same process as conjoined twins: the zygote begins to split but fails to completely separate. This condition may also be a symptom of repeated occurrences of continuous inbreeding in a genetic line.

No surgical outcomes studies exist for evaluating the function of the thumbs after an on-top plasty reconstruction.

Different features of the dysostosis are significant. Radiological imaging helps confirm the diagnosis. During gestation (pregnancy), clavicular size can be calculated using available nomograms. Wormian bones can sometimes be observed in the skull.

Diagnosis of CCD spectrum disorder is established in an individual with typical clinical and radiographic findings and/or by the identification of a heterozygous pathogenic variant in RUNX2 (CBFA1).

Few clinical outcome studies exist regarding the treatment of central polydactyly. Tada and colleagues note that satisfactory surgical correction of central polydactyly is difficult to achieve and that outcomes are generally poor. In Tada’s study, 12 patients were reviewed. All patients required secondary surgical procedures to address flexion contractures and angular deviation at the IP joint level.

However, several primary factors contribute to the complexity of central polydactyly reconstruction. Hypoplastic joints and soft tissues that predispose the reconstructed finger to joint contracture, and angular deformities as well as complex tendon anomalies, are often difficult to address. Therefore, treatment is wholly dependent on the anatomic components present, the degree of syndactyly, and the function of the duplicated finger.

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.

Specific types of additional body parts include:

- Accessory breast – one or more additional breasts

- Accessory spleen – one or more additional spleens

- Cervical rib – an additional rib

- Diphallia - Having two penes/penises.

- Hermaphroditism – having both sexes' sex organs

- Hyperdontia – additional teeth

- Pelvic digit – a bony growth in the soft tissue of the pelvic region

- Polycephaly – an extra head

- Polydactyly – additional fingers or toes

- Polymelia — an extra arm or leg.

- Polyorchidism – having three or more testicles

- Supernumerary bones – these additional bones are fairly common, particularly in the feet, and are frequently mistaken for fractures on x-rays.

- Supernumerary kidney – a third kidney

- Supernumerary nipples – an additional nipple

- Supernumerary phantom limbs – where the brain acts as though a limb were there, but it is not.

- Syndactyly – webbing between the fingers or toes

- Uterus didelphys – two vaginal canals and/or uteri

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.

Future studies will look further into the relationship of talon cusp and Rubinstein-Taybi syndrome and other oral-facial-digital syndromes. A former study showed a direct correlation in which 45 affected patients with Rubinstein-Taybi syndrome, 92% of these patients had talon cusp. Other researchers are attempting to trace talon cusp to ancestors and comparing dentition to modern humans. Another study done in 2007 examined the dentition of 301 Native American Indian skeletons for the presence or absence of talon cusp. The results showed five skeletons (2 percent) in the population had the trait.

In 2011, only 21 cases of talon cusp have been reported and are in literature. It appears that as of 2014 and 2015, additional research continues in hopes of finding the cause and mechanism of talon cusp. With the majority of cases of talon cusp being unreported, it remains difficult to conduct tests, come up with conclusions, conduct surgery and perform research with small numbers.

The diagnosis of IP is established by clinical findings and occasionally by corroborative skin biopsy. Molecular genetic testing of the NEMO IKBKG gene (chromosomal locus Xq28) reveals disease-causing mutations in about 80% of probands. Such testing is available clinically.

In addition, females with IP have skewed X-chromosome inactivation; testing for this can be used to support the diagnosis.

Many people in the past were misdiagnosed with a second type of IP, formerly known as IP1. This has now been given its own name - 'Hypomelanosis of Ito' (incontinentia pigmenti achromians). This has a slightly different presentation: swirls or streaks of hypopigmentation and depigmentation. It is "not" inherited and does not involve skin stages 1 or 2. Some 33–50% of patients have multisystem involvement — eye, skeletal, and neurological abnormalities. Its chromosomal locus is at Xp11, rather than Xq28.

Because polyorchidism is very uncommon, there is no standard treatment for the condition. Prior to advances in ultrasound technology, it was common practice to remove the supernumerary testicle. Several cases have been described where routine follow-up examinations conducted over a period of years showed that the supernumerary testicle was stable.

A meta-analysis in 2009 suggested removing non-scrotal supernumerary testicles because of the increased risk of cancer, and regular follow-up in the remaining cases to ensure that the supernumerary testicle remains stable.

In the 1960s and 1970s, several studies were conducted sponsored by the U.S. Atomic Energy Commission, with the aim of finding a link between genetics and hypodontia.

In the above brachydactyly syndromes, short digits are the most prominent of the anomalies, but in many other syndromes (Down syndrome, Rubinstein-Taybi syndrome, etc.), brachydactyly is a minor feature compared to the other anomalies or problems comprising the syndrome.

Around 5 years of age, surgical correction may be necessary to prevent any worsening of the deformity. If the mother has dysplasia, caesarian delivery may be necessary. Craniofacial surgery may be necessary to correct skull defects. Coxa vara is treated by corrective femoral osteotomies. If there is brachial plexus irritation with pain and numbness, excision of the clavicular fragments can be performed to decompress it. In case of open fontanelle, appropriate headgear may be advised by the orthopedist for protection from injury.

Treatment is only required if the occlusion or bite of the person is compromised and causing other dental problems. Multiple long-term clinical problems can arise such as occlusal interferences, aesthetic disturbances, loss of pulp vitality, irritation of tongue during mastication and speech, caries and displacement of the affected tooth. Most people with talon cusp will live their normal lives unless the case is severe and causes a cascade of other dental issues that lead to additional health problems. This dental anomaly would not be considered fatal. Generally talon cusps on lower teeth require no treatment, but talon cusps on upper teeth may interfere with the bite mechanics and may need to be removed or reduced.

Small talon cusps that produce no symptoms or complication for a person can remain untreated. However large talon cusps should not.

Some common treatments include:

- Fissure sealing

- Composite resin restoration

- Reduction of cusp

- Pulpotomy

- Root canal (endodontic treatment)

- Extraction

The condition is usually benign, but it can cause mild irritation to soft tissues around the teeth and the tongue, and if large enough, may pose an aesthetic problem. Talon cusps that are too large are filed down with a motorized file, and then endodontic therapy is administered.

In order to prevent any future dental complications, when talon cusp is present due to an early diagnosis it would be best to see a dentist regularly every six months for routine dental checkups, remain under observation, brush and floss properly and undergo regular topical applications of fluoride gel to prevent caries and to promote enamel strength.

The isochromosome i(12p) can be primarily detected in samples of skin fibroblasts, as well as in chorionic villus and amniotic fluid cell samples. Very rarely, it can also be detected in blood lymphocytes. It is also possible to detect the isochromosome in circulating lymphocytes, as well as other amniotic and placental samples. There is no strict limit as to where the isochromosome can be found. However, it is often unlikely that these samples will be tested when the blood karyotype is normal.

Using an ultrasound, Pallister-Killian may be diagnosed through observation of hypertelorism, broad neck, shorts limbs, abnormal hands or feet, diaphragmatic hernia, and hydramnios. Once born, a child may be diagnosed by observation of the syndrome's distinct facial features.

Synpolydactyly is a joint presentation of syndactyly (fusion of digits) and polydactyly (production of supernumerary digits). This is often a result of a mutation in the HOX D13 gene.

Types include:

Brachydactyly (Greek βραχύς = "short" plus δάκτυλος = "finger"), is a medical term which literally means "shortness of the fingers and toes" (digits). The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait. It most often occurs as an isolated dysmelia, but can also occur with other anomalies as part of many congenital syndromes.

Nomograms for normal values of finger length as a ratio to other body measurements have been published. In clinical genetics the most commonly used index of digit length is the dimensionless ratio of the length of the 3rd (middle) finger to the hand length. Both are expressed in the same units (centimeters, for example) and are measured in an open hand from the fingertip to the principal creases where the finger joins the palm and where the palm joins the wrist.

Most cases of polyorchidism are asymptomatic, and are discovered incidentally, in the course of treating another condition. In the majority of cases, the supernumerary testicle is found in the scrotum.

However, polyorchidism can occur in conjunction with cryptorchidism, where the supernumerary testicle is undescended or found elsewhere in the body. These cases are associated with a significant increase in the incidence of testicular cancer: 0.004% for the general population vs 5.7% for a supernumerary testicle not found in the scrotum.

Polyorchidism can also occur in conjunction with infertility, inguinal hernia, testicular torsion, epididymitis, hydrocele testis and varicocele. However, it is not clear whether polyorchidism causes or aggravates these conditions, or whether the existence of these conditions leads sufferers to seek medical attention and thus become diagnosed with a previously undetected supernumerary testicle.

A supernumerary nipple (also known as a third nipple, triple nipple, accessory nipple, polythelia or the related condition: polymastia) is an additional nipple occurring in mammals, including humans. Often mistaken for moles, supernumerary nipples are diagnosed in humans at a rate of approximately 1 in 18 people.

The nipples appear along the two vertical "milk lines," which start in the armpit on each side, run down through the typical nipples and end at the groin. They are classified into eight levels of completeness from a simple patch of hair to a milk-bearing breast in miniature.

"Polythelia" refers to the presence of an additional nipple alone while "polymastia" denotes the much rarer presence of additional mammary glands.

Although usually presenting on the milk line, pseudomamma can appear as far away as the foot.

A possible relationship with mitral valve prolapse has been proposed.

There does not yet exist a specific treatment for IP. Treatment can only address the individual symptoms.

Hemihypertrophy, now more commonly referred to as hemihyperplasia in the medical literature, is a condition in which one side of the body or a part of one side of the body is larger than the other to an extent considered greater than the normal variation. As it is difficult to establish a set clinical criteria for diagnosis of hemihyperplasia, the dictum is often used that the clinician should be able to see the asymmetry "from the end of the bed".

Hemihyperplasia is a congenital overgrowth disorder and the asymmetry can range from mild to severe. It is important to establish a diagnosis because hemihyperplasia is associated with an increased risk for embryonal tumors, mainly Wilms tumor and hepatoblastoma. Due to the heightened tumor risk, there is a tumor screening protocol that is recommended for all children with isolated hemihyperplasia and Beckwith-Wiedemann Syndrome. Some of the other syndromes associated with hemihyperplasia may also follow this tumor surveillance protocol. The recommended tumor surveillance protocol is:

1. Any child with suspected isolated hemihyperplasia should be referred to a clinical geneticist for evaluation.

2. Abdominal ultrasound every 3 months until 7 years

3. Serum alpha fetoprotein measurement every 3 months until 4 years

4. Daily caretaker abdominal examination at the discretion of the provider/parent

In some cases, children with hemihyperplasia may have different leg lengths. There are two main surgical options for the treatment of uneven leg lengths- shortening and lengthening. Epiphysiodesis, which involves removing part of the growth plate of the longer leg, allowing the shorter leg to "catch up", may be performed on patients still able to grow. Bone resection is performed on patients who have no growth left and involves removing part of the bone. Leg lengthening procedures are more painful, involving the insertion of pins to be turned, moving parts of the bone apart (Ilizarov's Method). This process is reserved mainly for patients with a discrepancy greater than 4 cm, although some leg lengthening procedures are now done cosmetically. Non-surgical options include attachment of a lift to the shoe, allowing the patient to walk normally.

Children with hemihypertrophy may also develop scoliosis, a curvature of the spine.

Hemifacial hyperplasia is believed to be a minor form of hemihypertrophy.

In some cases, the accessory breast may not be visible at the surface. In these cases, it may be possible to distinguish their appearance from normal breast tissue with MRI. In other cases, accessory breasts have been known to lactate, as illustrated in a woodcut showing a child nursing at ectopic breast tissue on the lateral thigh.

There is some evidence that the condition may be more common in Native American populations.

The oral rehabilitation of hypodontia, especially where a significant number of teeth have not developed, is often a multidisciplinary process, involving a specialist orthodontist, a consultant in restorative dentistry, and a paediatric dentist in the earlier years. The process of treating and managing hypodontia begins in the early years of the patient's dentition where absent teeth are identified and the process of maintaining the remaining teeth begins. This is largely conducted by the paediatric dentist with orthodontic input. Once all the adult teeth have erupted the orthodontist is likely to liaise with the restorative dentist regarding optimal positioning of teeth for subsequent replacement with prosthodontic methods. This may include the utilisation of a resin-retained bridge and implants for spaces or composite resin, veneers or crowns where teeth are diminutive or misshaped.

Because an individual with an enchondroma has few symptoms, diagnosis is sometimes made during a routine physical examination, or if the presence of the tumor leads to a fracture. In addition to a complete medical history and physical examination, diagnostic procedures for enchondroma may include the following:

- x-ray - On plain film, an enchondroma may be found in any bone formed from cartilage. They are lytic lesions that usually contain calcified chondroid matrix (a "rings and arcs" pattern of calcification), except in the phalanges. They may be central, eccentric, expansile or nonexpansile.

Differentiating an enchondroma from a bone infarct on plain film may be difficult. Generally, an enchondroma commonly causes endosteal scalloping while an infarct will not. An infarct usually has a well-defined, sclerotic serpentine border, while an enchondroma will not. When differentiating an enchondroma from a chondrosarcoma, the radiographic image may be equivocal; however, periostitis is not usually seen with an uncomplicated enchondroma.

- radionuclide bone scan - a nuclear imaging method to evaluate any degenerative and/or arthritic changes in the joints; to detect bone diseases and tumors; to determine the cause of bone pain or inflammation. This test is to rule out any infection or fractures.

- magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of organs and structures within the body. This test is done to rule out any associated abnormalities of the spinal cord and nerves.

- computed tomography scan (Also called a CT or CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, and organs. CT scans are more detailed than general x-rays.

If severe pain persists after the first 24hours it is recommended that an individual consult with a professional who can make a diagnosis and implement a treatment plan so the patient can return to everyday activities (Flegel, 2004). These are some of the tools that a professional can use to help make a full diagnosis;

Nerve conduction studies may also be used to localize nerve dysfunction ("e.g.", carpal tunnel syndrome), assess severity, and help with prognosis.

Electrodiagnosis also helps differentiate between myopathy and neuropathy.

Ultimately, the best method of imaging soft tissue is magnetic resonance imaging (MRI), though it is cost-prohibitive and carries a high false positive rate.