Pectus excavatum occurs in an estimated 1 in 150 to 1 in 1000 births, with male predominance (male-to-female ratio of 3:1). In 35% to 45% of cases family members are affected.

Researchers are unsure of the cause of pectus excavatum but assume that there is a genetic component for at least some of the cases as 37% of individuals have an affected first degree family member. As of 2012, a number of genetic markers for pectus excavatum have also been discovered.

Pectus excavatum is a relatively common symptom of Noonan syndrome, Marfan syndrome and Loeys-Dietz syndrome and sometimes is found in other connective tissue disorders such as Ehlers–Danlos Syndrome. Many children with spinal muscular atrophy develop pectus excavatum due to their diaphragmatic breathing. Pectus excavatum also occurs in about 1% of persons diagnosed with celiac disease for unknown reasons.

First described by Smith (1953), and elaborated upon by Cameron et al. (1976), internal pancreatic fistulas can result in pancreatic ascites, mediastinital pseudocysts, enzymatic mediastinitis, or pancreatic pleural effusions, depending on the flow of pancreatic secretions from a disrupted pancreatic duct or leakage from a pseudocyst.

Physiologically, increased pressure "in utero", rickets and increased traction on the sternum due to abnormalities of the diaphragm have been postulated as specific mechanisms. Because the heart is located behind the sternum, and because individuals with pectus excavatum have been shown to have visible deformities of the heart seen both on radiological imaging and after autopsies, it has been hypothesized that there is impairment of function of the cardiovascular system in individuals with pectus excavatum. While some studies have demonstrated decreased cardiovascular function, no consensus has been reached based on newer physiological tests such as echocardiography of the presence or degree of impairment in cardiovascular function. Similarly, there is no consensus on the degree of functional improvement after corrective surgery; A 2013 meta-analysis yielded conflicting results.

An external pancreatic fistula is an abnormal communication between the pancreas (actually pancreatic duct) and the exterior of the body via the abdominal wall.

Loss of bicarbonate-rich pancreatic fluid via a pancreatic fistula can result in a hyperchloraemic or normal anion gap metabolic acidosis. Loss of a small volume of fluid will not cause a problem but an acidosis is common if the volume of pancreatic fluid lost from the body is large.

There are few studies of the long-term outcomes of patients treated for MALS. According to Duncan, the largest and more relevant late outcomes data come from a study of 51 patients who underwent open surgical treatment for MALS, 44 of whom were available for long-term follow-up at an average of nine years following therapy. The investigators reported that among patients who underwent celiac artery decompression and revascularization, 75% remained asymptomatic at follow-up. In this study, predictors of favorable outcome included:

- Age from 40 to 60 years

- Lack of psychiatric condition or alcohol use

- Abdominal pain that was worse after meals

- Weight loss greater than 20 lb (9.1 kg)

Mechanistically, the causes of pelvic floor dysfunction are two-fold: widening of the pelvic floor hiatus and descent of pelvic floor below the pubococcygeal line, with specific organ prolapse graded relative to the hiatus. Associations include obesity, menopause, pregnancy and childbirth. Some women may be more likely to developing pelvic floor dysfunction because of an inherited deficiency in their collagen type. Some women may have congenitally weak connective tissue and fascia and are therefore at risk of stress urinary incontinence and pelvic organ prolapse.

By definition, "postpartum" pelvic floor dysfunction only affects women who have given birth, though pregnancy rather than birth or birth method is thought to be the cause. A study of 184 first-time mothers who delivered by Caesarean section and 100 who delivered vaginally found that there was no significant difference in the prevalence of symptoms 10 months following delivery, suggesting that pregnancy is the cause of incontinence for many women irrespective of their mode of delivery. The study also suggested that the changes which occur to the properties of collagen and other connective tissues during pregnancy may affect pelvic floor function.

Pelvic floor dysfunction can result after treatment for gynegological cancers.

Studies have shown that obesity of the mother increases the risk of neural tube disorders such as iniencephaly by 1.7 fold while severe obesity increases the risk by over 3 fold.

The two major risk factors for esophageal squamous-cell carcinoma are tobacco (smoking or chewing) and alcohol. The combination of tobacco and alcohol has a strong synergistic effect. Some data suggest that about half of all cases are due to tobacco and about one-third to alcohol, while over three-quarters of the cases in men are due to the combination of smoking and heavy drinking. Risks associated with alcohol appear to be linked to its aldehyde metabolite and to mutations in certain related enzymes. Such metabolic variants are relatively common in Asia.

Other relevant risk factors include regular consumption of very hot drinks (over 65 °C)(149 Fahrenheit) and ingestion of caustic substances. High levels of dietary exposure to nitrosamines (chemical compounds found both in tobacco smoke and certain foodstuffs) also appear to be a relevant risk factor. Unfavorable dietary patterns seem to involve exposure to nitrosamines through processed and barbecued meats, pickled vegetables, etc., and a low intake of fresh foods. Other associated factors include nutritional deficiencies, low socioeconomic status, and poor oral hygiene. Chewing betel nut (areca) is an important risk factor in Asia.

Physical trauma may increase the risk. This may include the drinking of very hot drinks.

Pelvic floor dysfunction refers to a wide range of issues that occur when muscles of the pelvic floor are weak, tight, or there is an impairment of the sacroiliac joint, lower back, coccyx, or hip joints. Symptoms include pelvic pain, pressure, pain during sex, incontinence, incomplete emptying, and visible organ protrusion. Tissues surrounding the pelvic organs may have increased or decreased sensitivity or irritation resulting in pelvic pain. Many times, the underlying cause of pelvic pain is difficult to determine. The condition affects up to 50% of women.

Pelvic floor dysfunction may include any of a group of clinical conditions that includes urinary incontinence, fecal incontinence, pelvic organ prolapse, sensory and emptying abnormalities of the lower urinary tract, defecatory dysfunction, sexual dysfunction and several chronic pain syndromes, including vulvodynia. The three most common and definable conditions encountered clinically are urinary incontinence, anal incontinence and pelvic organ prolapse.

Once a mother has given birth to a child with iniencephaly, risk of reoccurrence increases to 1-5%.

Splenic flexure syndrome is a term sometimes used to describe bloating, muscle spasms of the colon, and upper abdominal discomfort thought to be caused by trapped gas at the splenic (as opposed to hepatic) flexure in the colon; the pain caused can be excruciating and debilitating, and may mimic that of a heart attack (because of the proximity of the splenic flexure to the diaphragm and referred pain from irritation to the diaphragmatic sensory nerves).

Some physicians classify splenic flexure syndrome as a type of IBS; others consider it a separate condition.

Male predominance is particularly strong in this type of esophageal cancer, which occurs about 7 to 10 times more frequently in men. This imbalance may be related to the characteristics and interactions of other known risk factors, including acid reflux and obesity.

The long-term erosive effects of acid reflux (an extremely common condition, also known as gastroesophageal reflux disease or GERD) have been strongly linked to this type of cancer. Longstanding GERD can induce a change of cell type in the lower portion of the esophagus in response to erosion of its squamous lining. This phenomenon, known as Barrett's esophagus, seems to appear about 20 years later in women than in men, maybe due to hormonal factors. Having symptomatic GERD or bile reflux makes Barrett's esophagus more likely, which in turn raises the risk of further changes that can ultimately lead to adenocarcinoma. The risk of developing adenocarcinoma in the presence of Barrett's esophagus is unclear, and may in the past have been overestimated.

Being obese or overweight both appear to be associated with increased risk. The association with obesity seems to be the strongest of any type of obesity-related cancer, though the reasons for this remain unclear. Abdominal obesity seems to be of particular relevance, given the closeness of its association with this type of cancer, as well as with both GERD and Barrett's esophagus. This type of obesity is characteristic of men. Physiologically, it stimulates GERD and also has other chronic inflammatory effects.

"Helicobacter pylori" infection (a common occurrence thought to have affected over half of the world's population) is not a risk factor for esophageal adenocarcinoma and actually appears to be protective. Despite being a cause of GERD and a risk factor for gastric cancer, the infection seems to be associated with a reduced risk of esophageal adenocarcinoma of as much as 50%. The biological explanation for a protective effect is somewhat unclear. One explanation is that some strains of "H. pylori" reduce stomach acid, thereby reducing damage by GERD. Decreasing rates of "H. pylori" infection in Western populations over recent decades, which have been linked to better hygiene and increased refrigeration of food, could be a factor in the concurrent increase in esophageal adenocarcinoma.

Female hormones may also have a protective effect, as EAC is not only much less common in women but develops later in life, by an average of 20 years. Although studies of many reproductive factors have not produced a clear picture, risk seems to decline for the mother in line with prolonged periods of breastfeeding.

Tobacco smoking increases risk, but the effect in esophageal adenocarcinoma is slight compared to that in squamous cell carcinoma, and alcohol has not been demonstrated to be a cause.

It is estimated that in 10-24% of normal, asymptomatic individuals the median arcuate ligament crosses in front of (anterior to) the celiac artery, causing some degree of compression. Approximately 1% of these individuals exhibit severe compression associated with symptoms of MALS. The syndrome most commonly affects individuals between 20 and 40 years old, and is more common in women, particularly thin women.

Rupture of the urethra is an uncommon result of penile injury, incorrect catheter insertion, straddle injury, or pelvic girdle fracture. The urethra, the muscular tube that allows for urination, may be damaged by trauma. When urethral rupture occurs, urine may extravasate (escape) into the surrounding tissues. The membranous urethra is most likely to be injured in pelvic fractures, allowing urine and blood to enter the deep perineal space and subperitoneal spaces via the genital hiatus. The spongy urethra is most likely to be injured with a catheter or in a straddle injury, allowing urine and blood to escape into the scrotum, the penis, and the superficial peritoneal space. Urethral rupture may be diagnosed with a cystourethrogram. Due to the tight adherence of the fascia lata, urine from a urethral rupture cannot spread into the thighs.

The mortality rate of meconium-stained infants is considerably higher than that of non-stained infants; meconium aspiration used to account for a significant proportion of neonatal deaths. Residual lung problems are rare but include symptomatic cough, wheezing, and persistent hyperinflation for up to five to ten years. The ultimate prognosis depends on the extent of CNS injury from asphyxia and the presence of associated problems such as pulmonary hypertension. Fifty percent of newborns affected by meconium aspiration would die fifteen years ago; however, today the percent has dropped to about twenty.

In a study conducted between 1995 and 2002, MAS occurred in 1,061 of 2,490,862 live births, reflecting an incidence of 0.43 of 1,000. MAS requiring intubation occurs at higher rates in pregnancies beyond 40 weeks. 34% of all MAS cases born after 40 weeks required intubation compared to 16% prior to 40 weeks.

If splenectomy is performed for conditions in which blood cells are sequestered in the spleen, failure to remove accessory spleens may result in the failure of the condition to resolve. During medical imaging, accessory spleens may be confused for enlarged lymph nodes or neoplastic growth in the tail of the pancreas, gastrointestinal tract, adrenal glands or gonads.

Rumination disorder was initially documented

as affecting newborns,

infants, children

and individuals with mental and functional disabilities (the cognitively handicapped).

It has since been recognized to occur in both males and females of all ages and cognitive abilities.

Among the latter, it is described with almost equal prevalence among infants (6–10% of the population) and institutionalized adults (8–10%).

In infants, it typically occurs within the first 3–12 months of age.

The occurrence of rumination syndrome within the general population has not been defined. Rumination is sometimes described as rare, but has also been described as not rare, but rather rarely recognized.

The disorder has a female predominance. The typical age of adolescent onset is 12.9, give or take 0.4 years (±), with males affected sooner than females (11.0 ± 0.8 for males versus 13.8 ± 0.5 for females).

There is little evidence concerning the impact of hereditary influence in rumination syndrome. However, case reports involving entire families with rumination exist.

Accessory spleens may be formed during embryonic development when some of the cells from the developing spleen are deposited along the path from the midline, where the spleen forms, over to its final location on the left side of the abdomen by the 9th–11th ribs. The most common locations for accessory spleens are the hilum of the spleen and adjacent to the tail of the pancreas. They may be found anywhere along the splenic vessels, in the gastrosplenic ligament, the splenorenal ligament, the walls of the stomach or intestines, the pancreatic tail, the greater omentum, the mesentery or the gonads and their path of descent. The typical size is approximately 1 centimeter, but sizes ranging from a few millimeters up to 2–3 centimeters are not uncommon.

Splenogonadal fusion can result in one or more accessory spleens along a path from the abdomen into the pelvis or scrotum. The developing spleen forms near the urogenital ridge from which the gonads develop. The gonads may pick up some tissue from the spleen, and as they descend through the abdomen during development, they can produce either a continuous or a broken line of deposited splenic tissue.

Splenosis is a condition where foci of splenic tissue undergo autotransplantation, most often following physical trauma or splenectomy. Displaced tissue fragments can implant on well vascularized surfaces in the abdominal cavity, or, if the diaphragmatic barrier is broken, the thorax.

The cause of rumination syndrome is unknown. However, studies have drawn a correlation between hypothesized causes and the history of patients with the disorder. In infants and the cognitively impaired, the disease has normally been attributed to over-stimulation and under-stimulation from parents and caregivers, causing the individual to seek self-gratification and self-stimulus due to the lack or abundance of external stimuli. The disorder has also commonly been attributed to a bout of illness, a period of stress in the individual's recent past, and to changes in medication.

In adults and adolescents, hypothesized causes generally fall into one of either category: habit-induced, and trauma-induced. Habit-induced individuals generally have a history of bulimia nervosa or of intentional regurgitation (magicians and professional regurgitators, for example), which though initially self-induced, forms a subconscious habit that can continue to manifest itself outside the control of the affected individual. Trauma-induced individuals describe an emotional or physical injury (such as recent surgery, psychological distress, concussions, deaths in the family, etc.), which preceded the onset of rumination, often by several months.

Thoracic endometriosis affects women aged 15–54, who are between menarche and menopause. It can affect their qualify of life, with catamenial pneumothorax being the most common presentation.

An abdominal pregnancy can be regarded as a form of an ectopic pregnancy where the embryo or fetus is growing and developing outside the womb in the abdomen, but not in the Fallopian tube, ovary or broad ligament.

While rare, abdominal pregnancies have a higher chance of maternal mortality, perinatal mortality and morbidity compared to normal and ectopic pregnancies; on occasion, however, a healthy viable infant can be delivered.

Because tubal, ovarian and broad ligament pregnancies are as difficult to diagnose and treat as abdominal pregnancies, their exclusion from the most common definition of abdominal pregnancy has been debated.

Others—in the minority—are of the view that abdominal pregnancy should be defined by a placenta implanted into the peritoneum.

Risk factors are similar to tubal pregnancy with sexually transmitted disease playing a major role; however about half of those with ectopic pregnancy have no known risk factors (which include damage to the Fallopian tubes from previous surgery or from previous ectopic pregnancy, and tobacco smoking).

The meniscal tear is the most common knee injury. A meniscal tear tends to be more frequent in sports that have rough contact or pivoting sports such as soccer. The meniscal tear is more common in males than females. The ratio is about two and a half males to one female. Males between the ages of thirty-one and forty tend to tear their meniscus more frequently than younger men. Females on the other hand, seem to be more likely to tear their meniscus between the ages of eleven and twenty. People who work in straining jobs such as construction or pro athletes are also more likely to have a meniscal tear because of all the different tensions of their knees. According to the United States National Library of Medicine, the isolated medial meniscal tear occurs more frequently than any other tear associated with the meniscus. The prevalence of meniscus tears is the same for both knees. In a few different studies the BMI of a person can have a greater effect on the frequency of a meniscus tear because having a higher BMI will result in more weight on the joints which can cause the knee to be non-aligned which causes more weight on the muscles resulting in an easier tear. In 2008 the U.S Department of Health and Human Services reported a combined total of 2,295 discharges for the principal diagnosis of tear of lateral cartilage/meniscus (836.0), tear of medial cartilage/meniscus (836.1), and tear of cartilage/meniscus (836.2). Females had a total of 53.49% discharges while males had 45.72%. Individuals between the ages of 45–68 years had an average of 31.73% discharges followed by age group 65–84 with 28.82%. The average length of stay for a patient diagnosed with torn menisci was 2.7 days for males and 3.7 days for females. There was a report of 6,941 hospital discharges for knee repair. Individuals between 18–44 years of age were among the highest with 37.37% total of discharges followed by the age group 45–64 with a percentage of 36.34%. Males had a slightly higher number of discharges (50.78%) than females (48.66%). The average length of stay for both male and female patients in a hospital setting was 3.1.

This has a poor prognosis, as it is a fixed abnormality. Causes include post-term pregnancy, placental insufficiency, and NSAID use by the mother.