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PubMed2004

Does conflict between home and work explain the effect of multiple roles on mental health? A comparative study of Finland, Japan, and the UK.

BACKGROUND: Although there have been a number of studies on the effects of multiple roles on health and how a combination of work and family roles may be either advantageous (role enhancement) or disadvantageous (role strain) for health, there has been relatively little investigation on the psychosocial content of such roles. Work-to-family conflict and family-to-work conflict could arise from inability to combine multiple roles and result in stress and ill health. The question of whether both types of conflict mediate between the association of multiple roles with health has not been analysed before. This paper sets out to investigate whether: (1) work-to-family conflict or family-to-work conflict contributes towards explaining the association of multiple roles with mental health; (2) the effect of work-to-family conflict and family-to-work conflict on mental health varies by gender; (3) the effect of work-to-family and family-to-work conflict on mental health vary between countries with different welfare state arrangements and social norms. METHODS: Cross-sectional data of economically active male and female public sector employees aged 35-60 in London (UK), Helsinki (Finland), and the West Coast of Japan. Linear regression models (separate for each gender and cohort) of SF-36 mental component scores were analysed with role combinations, family-to-work and work-to-family conflict as explanatory variables. RESULTS: Single fathers in all three cohorts and of single mothers in the Helsinki cohort had poor mental health, and this was partly explained by their higher levels family-to-work conflict. Both types of conflict affect the mental health of men and women independently of each other. Japanese women had the greatest conflict and poorest mental health while Helsinki women had the lowest conflict and best mental health. CONCLUSION: Both work-to-family and family-to-work conflict affect the mental health of men and women in three different countries. Work and family roles and the balance between the two may be important for the mental health of men and women in industrialized societies. Any analysis of the effect of multiple roles on health needs to take into account the psychosocial content of such roles.

Adult↗

PubMed2005

Explaining socioeconomic inequality in mortality among South Koreans: an examination of multiple pathways in a nationally representative longitudinal study.

BACKGROUND: South Korea has a different cause-specific structure of mortality compared with North America and northern European countries where studies on pathways to socioeconomic mortality inequalities have been performed. We examined the ability of multiple pathways to explain socioeconomic differentials in all-cause mortality in South Korea. METHODS: The 1998 National Health and Nutrition Survey data of South Korea were linked to data on mortality. The socioeconomic position (SEP) indicator was household income. Twelve variables represented biological risk factors (body mass index, systolic blood pressure, cholesterol, and glucose), health behaviours (smoking, alcohol consumption, and regular exercise), psychosocial factors (feelings of sadness and depression, perceived level of stress, and marital status), and early life exposures (education and adulthood height). RESULTS: Mortality differentials by income level did not decrease after exclusion of subjects with severe chronic illness or functional limitation. Biological risk factors, health behaviours, and psychosocial factors caused minor reductions in relative risk for income levels. The ability of early life exposures to explain socioeconomic differentials in mortality was greater than that of biological risk factors, health behaviours, and psychosocial factors. CONCLUSIONS: The contribution of multiple pathways to socioeconomic differentials in all-cause mortality may vary in place with the different cause-specific structure of mortality. Future studies with specific pathway variables and specific disease outcomes would provide better understanding of causal mechanisms between SEP and health.

Blood Glucose↗

PubMed2006

Explaining variability in the relationship between antiretroviral adherence and HIV mutation accumulation.

OBJECTIVES: Determining the relationship between antiretroviral adherence and resistance accumulation is important for the design and evaluation of adherence interventions. Our objective was to explain heterogeneity observed in this relationship. METHODS: We first conducted a systematic review to locate published reports describing the relationship between adherence and resistance. We then used a validated computer simulation to simulate the patient populations in these reports, exploring the impact of changes in individual patient characteristics (age, CD4, viral load, prior antiretroviral experience) on the shape of the adherence-resistance (A-R) curve. RESULTS: The search identified 493 titles, of which 3 contained relevant primary data and 2 had sufficient follow-up for inclusion (HOMER and REACH cohorts). When simulating HOMER, the A-R curve had a high peak with a greatly increased hazard ratio (HR) of accumulating mutations at partial compared to complete adherence (simulation, HR 2.9; HOMER, HR 2.7). When simulating REACH, the A-R curve had a shallow peak with a slightly increased hazard of accumulating mutations at partial adherence (simulation, HR 1.2; REACH, HR 1.4). This heterogeneity was primarily attributable to differences in antiretroviral experience between the cohorts. CONCLUSIONS: Our computer simulation was able to explain much of the heterogeneity in observed A-R curves.

Anti-Retroviral Agents↗

PubMed1999

Underreporting of habitual food intake is explained by undereating in highly motivated lean women.

Underreporting of habitual food intake can be explained by underrecording and/or undereating. This study was designed to discriminate between the two errors mentioned, by measuring energy and water balance. Twenty-four lean female dieticians were recruited as subjects. Energy intake and water intake were measured for 1 wk with a weighed dietary record. Energy expenditure was estimated from measurements of resting metabolic rate, and measured physical activity with a triaxial accelerometer for movement registration. Water loss was estimated with deuterium-labeled water. Energy balance was determined by measuring the change in body mass over a nonrecording week (preceding the recording week) and over the recording week. Mean energy and water intake were 8.5 +/- 1.0 MJ/d and 2.3 +/- 0.5 L/d. The change in body mass in the nonrecording week was 0.1 +/- 0.6 kg and in the recording week -0.6 +/- 0.8 kg (paired t test; P = 0.02), indicating 16% undereating. Recorded water intake plus calculated metabolic water closely matched measured water loss (r = 0.93; P = 0.0001), which indicated a high recording precision. In conclusion, in the studied group of highly motivated lean women, there was 16% underreporting of habitual food intake, which could be explained by undereating.

Adult↗

PubMed2004

Breast cancer and the brain: a neurodevelopmental hypothesis to explain the opposing effects of caloric deprivation during the Dutch famine of 1944-1945 on breast cancer and its risk factors.

Most studies on calorie deprivation and cancer risk in rodents show reductions in tumor occurrence. However, the few human studies on calorie restriction are conflicting. An overview is given of results in the DOM (diagnostic onderzoek mammacarcinoom) cohorts among women exposed to the Dutch Famine of 1944-1945. Opposing effects were found on risk factors (shortening of leg length, later menarche, and earlier menopause), whereas urinary estrogens and plasma insulin-like growth factor (IGF)-1 and IGF binding protein-3 were increased, as was breast cancer itself. Exposure between 2 and 10 y old was an unexpected window of susceptibility to the effects of calorie deprivation. The effects of famine exposure were most clearly seen in women who never gave birth. These opposing observations can be explained by a neurodevelopmental hypothesis on set-point shifts at the level of the diencephalons/hypothalamus, either directly or from rebound effects. Such a mechanism reflects old evolutionary adaptation systems in lower and higher organisms to cope with periods of stress and famine by adjusting, for example, reproductive functions. These effects in exposed women may later also affect their unexposed offspring. This hypothesis provides several testable, hormone-mediated corollaries on the relationships between the role of calories in a Westernized lifestyle and human cancer risk. The underlying developmental perspective, as opposed to a risk factor approach, can explain why certain ages, even before breast development, are especially sensitive to effects of large fluctuations in calories. The observations presented may have implications for preventive strategies such as promoting moderation of calorie intake to curb cancer risks.

Adult↗

PubMed1994

Are racial differences in squamous cell esophageal cancer explained by alcohol and tobacco use?

BACKGROUND: In the United States, incidence rates of squamous cell esophageal cancer are more than five times higher among black men than among white men. Reasons that might explain this large racial disparity are being sought. PURPOSE: We evaluated whether differential use of alcohol and tobacco can fully account for the excess of squamous cell esophageal cancer among U.S. blacks. METHODS: We conducted a population-based, case-control study with in-person interviews with 373 squamous cell esophageal cancer case patients (124 white males and 249 black males) and 1364 control subjects (750 white males and 614 black males) from three U.S. geographic areas. Histologically confirmed cases of squamous cell esophageal cancer newly diagnosed from August 1, 1986, through April 30, 1989, among white and black men aged 30-79 years were included. RESULTS: Alcohol use of more than one drink per day and/or current cigarette use of at least one pack per day accounted for 92.7% (95% confidence interval [CI] = 86.8%-98.5%) of the squamous cell esophageal cancers in blacks, versus 86.3% (95% CI = 75.5%-97.1%) in whites, and for 94% of the difference between the black and white annual incidence rates. The interaction between race and the continuous drinking/smoking variable in a logistic regression analysis was statistically significant (two-sided, P = .02). Exposure rates among controls at all levels of combined alcohol and tobacco use examined were slightly higher among blacks and accounted for a small portion of the racial differences in incidence rates. CONCLUSION: Although the vast majority of esophageal cancers in both blacks and whites in our data can be explained by use of alcohol and tobacco, it is not clear why heavy consumption of alcohol and/or tobacco is responsible for 14.9 per 100,000 per year more cases of squamous cell esophageal cancer among blacks than among whites. The differences in the odds ratios appear to account for more of the racial differences in incidence rates than do the prevalences of exposure to alcohol and tobacco alone. The reasons for this apparent racial difference in carcinogenic risk from the same level of alcohol and tobacco use are unknown, but they may include qualitative differences in alcohol consumption, differences in other environmental exposures that interact with alcohol and/or tobacco to modify risks, or differences in susceptibility to these factors.

Adult↗

PubMed2006

Can deleterious mutations explain the time dependency of molecular rate estimates?

It has recently been observed by Ho et al. (Ho SYW, Phillips MJ, Cooper A, Drummond AJ. 2005. Time dependency of molecular rate estimates and systematic overestimation of recent divergence times. Mol Biol Evol. 22(7):1561-1568) that apparent rates of molecular evolution increase when measured over short timespans. I investigate whether the data are explainable purely by deleterious mutations. I derive an empirical approximation for the persistence of these mutations in a randomly mating population and, hence, derive lower limits on effective population sizes. These limits are high and get higher if additional reasonable assumptions are made. This casts doubt on whether deleterious mutations are able to explain the apparent rate acceleration.

Animals↗

PubMed1995

A challenge to the concept of tubal reflux to explain the rise and fall of CA125 in serum during the first trimester.

Although amniotic fluid concentrations of cancer antigen (CA) 125 rise during the first two trimesters of pregnancy, the serum concentrations of CA125 peak during the first trimester and drop to non-pregnant values in the second and third trimester. A previous hypothesis to explain this phenomenon was that in the early first trimester decidual CA125 gains access to the maternal compartment via 'tubal reflux' and subsequent absorption by peritoneal lymphatics. However, as pregnancy advances, the decidua capsularis fuses with the decidua parietalis, thus obliterating the endometrial cavity at 10-12 weeks; the Fallopian tubes thus become functionally obstructed. To test this hypothesis, we evaluated early first trimester CA125 concentrations in women conceiving by in-vitro fertilization (IVF) and embryo transfer with patent tubes (group 1) and in those conceiving by IVF and embryo transfer with bilateral tubal occlusion (group 2). We also compared those conceiving with human menopausal gonadotrophin therapy for ovulation induction without assisted reproduction (group 3) and those conceiving without fertility drugs in assisted reproduction (group 4). Mean CA125 concentrations were similar in groups 1-3; the mean CA125 concentration in group 4 was lower but this difference was not statistically significant, probably due to the small sample size. These data do not support the concept that tubal reflux explains the rise and fall of serum concentrations of CA125, since these were equal in IVF conceptions with or without tubal patency.

CA-125 Antigen↗

PubMed1998

The PRIME study: classical risk factors do not explain the severalfold differences in risk of coronary heart disease between France and Northern Ireland. Prospective Epidemiological Study of Myocardial Infarction.

We are studying the contribution of risk and genetic factors, and their interaction, to the development of ischaemic heart disease (IHD) and other cardiovascular endpoints. The study is prospective, based in three centres in the south, east and north of France and in Northern Ireland. A total of 10,592 men aged 50-59 years were recruited from 1991 to 1993, and examined for evidence of IHD at baseline. Subjects are followed annually by questionnaire. Clinical information is validated from hospital and GP records. Demographic characteristics were similar in all four centres. Body mass index was highest in Strasbourg (mean 27.4 kg/m2 vs. 26.3 kg/m2 in Toulouse and Belfast), but total cholesterol, triglyceride and fibrinogen were highest in Belfast. In Belfast, 6.1% reported having had a coronary angiogram, compared to 3.0% in Toulouse. Conversely, 13.8% in Toulouse reported taking lipid-lowering drugs vs. 1.6% in Belfast. As predicted, a history of myocardial infarction (MI) was highest in Belfast (6.1%) and lowest in Toulouse (1.2%). Some 7.1% of Belfast men reported a medical diagnosis of angina vs. 1.5% in Toulouse. Subjects showing evidence of pre-existing IHD will be studied prospectively but treated in the analysis as an additional variable. These results provide a measure of reassurance that these cohorts are representative of the communities from which they are drawn and provide a reliable baseline for prospective evaluation and cross-sectional comparisons. The levels of the classical risk factors found in this study, particularly when examined in combination, as multiple logistic functions based on previous British studies, are very similar between centres and cannot explain the large differences in the incidence of IHD which exist. Additional risk factors may help explain, at least in part, the major differences in incidence of IHD between these study centres.

Anthropometry↗

PubMed1985

Increased daily sperm production in the breeding season of stallions is explained by an elevated population of spermatogonia.

Seasonal variation in number of spermatogonia and germ cell degeneration was evaluated to determine which mechanism might explain seasonal differences in daily sperm production per testis (DSP/testis) or per g parenchyma (DSP/g) in stallions. Comparing 28 adult stallions (4 to 20 yr old) in each of the nonbreeding (December-January) and breeding (June-July) seasons, the population of type A spermatogonia was more than two times greater (P less than 0.01) in the breeding season. While the number of type B spermatogonia also was elevated (P less than 0.01) in the breeding season, the number of type B spermatogonia/type A spermatogonium was similar (P greater than 0.05) between seasons. Daily sperm production/testis based on each cell type from type B spermatogonia to spermatids with elongated nuclei was lower (P less than 0.01) in the nonbreeding season. Based on DSP/g, there was significant degeneration during the meiotic divisions in the nonbreeding season. However, this reduction in potential spermatozoan production was not significant (P greater than 0.05) when considering DSP/testis. Significant germ cell degeneration also occurred in the breeding season between type B spermatogonia and primary spermatocytes. However, the type A spermatogonial population was sufficiently elevated to override this degeneration and to explain elevated production of sperm in the breeding season of stallions.

Animals↗

PubMed2000

Periischemic cerebral blood flow (CBF) does not explain beneficial effects of isoflurane on outcome from near-complete forebrain ischemia in rats.

BACKGROUND: Isoflurane improves outcome from near-complete forebrain ischemia in rats compared with fentanyl-nitrous oxide (N2O). Sympathetic ganglionic blockade with trimethaphan abolishes this beneficial effect. To evaluate whether anesthesia-related differences in cerebral blood flow (CBF) may explain these findings, this study compared regional CBF before, during, and after near-complete forebrain ischemia in rats anesthetized with either isoflurane (with and without trimethaphan) or fentanyl-nitrous oxide. METHODS: Fasted, normothermic isoflurane anesthetized Sprague-Dawley rats were prepared for near-complete forebrain ischemia (10 min of bilateral carotid occlusion and mean arterial pressure = 30 mmHg). After surgery, rats were anesthetized with either 1.4% isoflurane (with or without 2.5 mg of trimethaphan intravenously at onset of ischemia) or fentanyl-nitrous oxide (25 microgram. kg-1. h-1. 70% N2O-1). Regional CBF was determined (14C-iodoantipyrine autoradiography) before ischemia, 8 min after onset of ischemia, and 30 min after onset of reperfusion. RESULTS: Regional CBF did not differ significantly among groups at any measurement interval. Ischemia caused a marked flow reduction to 5% or less of baseline (P < 0.001) in selectively vulnerable regions, such as the cortex, caudoputamen and hippocampus, whereas flow in the brain stem and cerebellum was preserved. Reperfusion at 30 min was associated with partial restoration of flow to 35-50% of baseline values in ischemic structures. CONCLUSIONS: The results indicate that improved histologic-behavioral outcome provided by isoflurane anesthesia cannot be explained by differential vasodilative effects of the anesthetic states before, during, or after severe forebrain ischemia. This study also shows severe postischemic delayed hypoperfusion that was not affected by choice of anesthetic or the presence of trimethaphan. Mechanisms other than effects on periischemic CBF must be responsible for beneficial effects of isoflurane in this model.

Anesthetics, Inhalation↗

PubMed1996

What does not explain the variation in the direct costs of graduate medical education.

BACKGROUND: There is considerable variation in the costs of training residents across hospitals. Previous studies have reported training costs that ranged for $7,500 to $200,000 per resident, with means in the $50,000 to $60,000 range. This paper examines the factors associated with the variation in the direct costs of residency education across hospitals. METHODS: Hospital costs, hospital payment rates, various cost-of-living indices, and hospital characteristics for all hospitals in the United States receiving Medicare funds for residency education in fiscal year 1991 were obtained from various public sources. Bivariate and multivariate analyses were performed to determine whether organizational structure of residency training, specialty mix of residents, quality of training, cost of living in the geographic area, patient mix of the hospital, or other factors could explain some or all of the cost variation. RESULTS: Only a small proportion of the variation in the costs of training residents or payments for residency education could be explained by the factors analyzed. CONCLUSION: Much of the current variation in residency costs and payments is attributable to accounting and not structural or locational factors. Institutions looking for ways to become more efficient could compare costs of training across institutions without sophisticated adjusters. Federal policymakers should consider a national payment rate per resident to replace the current system based on hospital-specific costs. This proposal would redistribute dollars across residency programs. The proposal would affect payments for direct medical education in the Medicare program and could form the basis for payment for residency education by all payers.

Accounting↗

PubMed2003

Higher risk behaviour and rates of sexually transmitted diseases in Mwanza compared to Uganda may help explain HIV prevention trial outcomes.

OBJECTIVE: To determine to what extent the higher impact of treatment for sexually transmitted diseases (STD) on HIV incidence in Mwanza, Tanzania than in Rakai and Masaka, Uganda might be explained by baseline differences between the trial populations. DESIGN: A re-analysis of baseline data from the three trial populations comparing demography, sexual risk behaviour and HIV/STD epidemiology. METHODS: Data were compared after age-standardization and adjustments for sample selection where necessary. STD rates were also adjusted for the sensitivities and specificities of the diagnostic techniques used. RESULTS: Demographic patterns were similar across populations, apart from effects of AIDS on fertility and mortality (including widowhood) in Uganda. Higher sexual risk behaviours, including younger age of sexual debut, higher numbers of recent partners and lower frequency of condom use, were apparent in Mwanza compared to Masaka and Rakai. High-titre serological syphilis, gonorrhoea, chlamydia infection and trichomoniasis were all more prevalent in Mwanza, except for chlamydia infection in males. There was little difference between sites in the seroprevalence of Herpes simplex virus type-2. Age patterns in the prevalence of short-duration STD and current risk behaviours were similar across sites but all-titre serological syphilis was more prevalent among older participants in Rakai and Masaka than Mwanza. CONCLUSIONS: Differences between trial populations included higher reported risk behaviour and higher rates of curable STD in Mwanza compared to Rakai and Masaka. These differences probably relate to previous reductions in risk behaviour in Uganda and may explain, at least in part, the contrasting results of these trials.

Adolescent↗

PubMed1999

Defense styles explain psychiatric symptoms: an empirical study.

To examine the relation between psychiatric symptoms and defense mechanisms, we administered two questionnaires, the Symptom Check-list 90 (SCL-90) and the Defense Style Questionnaire (DSQ) to 122 psychiatric out-patients and to a community sample of 337 subjects. Using regression analysis, we found that 51.8% of the variation in subject's Global Severity Index value could be explained by his defense style. Of the three defense styles, the immature style explained most of the variation in the symptoms. We found little overall evidence for specific connections between particular defenses and symptoms. Projection and dissociation were central in most of the symptom dimensions. We compared patients and controls with the same level of general symptom severity and found that patients used significantly more devaluation and splitting, and controls used significantly more altruism and idealization. Whether defenses predispose to certain symptomatology or are one of its aspects is discussed.

Adolescent↗

PubMed1996

The importance of comorbidities in explaining differences in patient costs.

OBJECTIVES: The authors examine to what extent comorbidities contribute to differences in patient hospital costs. METHODS: The medical record data for this study were collected from 15 metropolitan Boston hospital for 4,439 patients admitted mostly in 1985 for one of eight common conditions. Massachusetts hospital discharge abstract data for 1985 and 1993 also were used. Comorbidities were identified from the medical record for the 15-hospital data set and from discharge abstracts for all cases. Stepwise regression models were used to develop comorbidity scores. RESULTS: Across all conditions, the medical record-based comorbidity score increased the R2 value from .42 in a model with diagnosis-related groups alone to .50. In condition-specific analyses, including the comorbidity score increased the R2 by more than 50% in six of eight conditions, and was more important than several other dimensions of severity in explaining condition-specific costs. When comorbidities were determined from discharge abstract data rather than medical records, only approximately half as much comorbidity was found. Also, there was much less explanatory power: the all-condition R2 only went from .42 to .44. However, a comorbidity score developed from statewide hospital discharge abstract data was more useful in explaining variations in charges in the eight condition-specific analyses conducted on patients 65 years and older. CONCLUSIONS: Comorbidities, particularly when determined from the medical record, are important determinants of patient costs.

Adolescent↗

PubMed1997

Explaining breast cancer mortality in England: the effect of socioeconomic factors and health care services.

England has the worst mortality rate for breast cancer in the developed world. Using area-level data for 145 health districts in England, this study seeks to explain variations in breast cancer mortality among women aged 50-64 years in the period before the National Breast Screening Programme became operational. It is found that socioeconomic and behavioural factors had a larger effect on mortality than did health care inputs. This might be explained both by inadequacies in the data, and by the fact that, in the absence of screening, cancers tend to be detected at a later stage, by which time the chances of a successful outcome are reduced. It is suggested that the impact of health care services in reducing mortality will increase in the future as screening becomes widespread and results in earlier detection and treatment. The prioritization of screening is central to achieving the reductions in mortality from breast cancer specified in the Health of the Nation targets.

Aged↗

PubMed2000

Lower HIV-2 plasma viral loads may explain differences between the natural histories of HIV-1 and HIV-2 infections.

To explain the low transmissibility and pathogenicity of HIV-2 infection's plasma viral loads in both HIV-1- and HIV-2-infected persons were compared by using the polymerase chain reaction (PCR)-based Amp-RT assay to measure levels of reverse transcriptase (RT) activity. The study comprised a total of 155 HIV-infected-people including 58 who were infected with HIV-2 with CD4+ cell counts <500 x 106/L (n = 15), CD4+ cell counts >500 x 106/L (n = 26), or with tuberculosis (TB; n = 17), and 97 HIV-1-infected people with CD4+ cell counts <500 x 106/L (n = 32), CD4+ cell counts >500 x 106/L (n = 25), or TB (n = 40). Among persons with CD4+ cell counts <500 x 106/L, 11 (73.3%) of 15 HIV-2-infected persons had detectable plasma RT activity compared with 25 (78.1%) of 32 HIV-1-infected persons (p =.725). However, the median HIV-2 plasma RT activity in this group was significantly lower (2561 x 10-10 U/ml; p =.036; detectable range, 1712-644,868 x 10-10 U/ml) than the RT activity of HIV-1-infected persons with similar CD4+ cell counts (13,241 x 10-10 U/ml; detectable range, 8482-1,478,880 x 10-10 U/ml). Among TB patients, 10 (58.8%) of 17 HIV-2-infected persons had detectable plasma RT activity compared with 30 (75%) of 40 HIV-1-infected persons (p =.342). In contrast, among patients with CD4+ cell counts >500 x 106/L, none of 26 HIV-2-infected persons had detectable RT activity compared with 13 (52%) of 25 HIV-1-infected persons (p <.001). Our data suggest that unlike HIV-1 infection, HIV-2 infections with CD4+ cell counts >500 x 106/L are associated with a low level of viral replication, which may explain the longer clinical latency and lower transmissibility seen in HIV-2 infection.

CD4 Lymphocyte Count↗

PubMed2003

A new theory to explain the genesis of petrous apex cholesterol granuloma.

OBJECTIVE: To propose a new hypothesis that attempts to explain the pathogenesis of petrous apex cholesterol granuloma (PA CG). CLASSIC OBSTRUCTION-VACUUM HYPOTHESIS: PA CGs form when mucosal swelling blocks the circuitous pneumatic pathways to the apical air cells. Trapped gas resorption results in a vacuum that triggers bleeding, and CG forms through anaerobic breakdown of blood products. PROBLEMS WITH THE CLASSIC (OBSTRUCTION-VACUUM) HYPOTHESIS: Impaired ventilation of mucosa-lined pneumatic tracts in the middle ear, mastoid, paranasal sinuses, and lung are very common, but CG is rare. The extraordinary levels of temporal bone pneumatization typically observed in PA CG cases is indicative of excellent ventilation and freedom from inflammatory mucosal disease. Were under pressure due to gas absorption alone sufficient to trigger hemorrhage, CG ought to be frequent in otitis media with effusion. PATIENTS: The opposite PA of 13 patients with PA CG compared with 31 highly pneumatic PAs in patients undergoing imagery for non-otologic reasons. MAIN OUTCOME MEASURE: The nature of the bony partition, as seen on computed tomography, between the PA air cell system and the adjacent marrow compartment. RESULTS: 4 of 13 PAs with CGs on the opposite side showed deficient septation between air cells and marrow, whereas this was not observed in any of the 31 extensively pneumatized normal ears. NEW HYPOTHESIS (EXPOSED MARROW): As cellular tracts penetrate the apex during young adulthood, budding mucosa invades and replaces hematopoietic marrow. The bony interface becomes deficient, with coaptation of richly vascular marrow and the mucosal air cell lining. Hemorrhage from the exposed marrow coagulates within the mucosal cells and occludes outflow pathways. Sustained hemorrhage from exposed marrow elements provides the engine responsible for the progressive cyst expansion. As the cyst expands, bone erosion increases the surface area of exposed marrow along the cyst wall. This exposed marrow theory explains the unique proclivity of the healthy and well-pneumatized PA to form a CG.

Adult↗