Primary spontaneous pneumothorax (PSP) has for many years been thought to be caused by "blebs" (small air-filled lesions just under the pleural surface), which were presumed to be more common in those classically at risk of pneumothorax (tall males) due to mechanical factors. In PSP, blebs can be found in 77% of cases, compared to 6% in the general population without a history of PSP. As these healthy subjects do not all develop a pneumothorax later, the hypothesis may not be sufficient to explain all episodes; furthermore, pneumothorax may recur even after surgical treatment of blebs. It has therefore been suggested that PSP may also be caused by areas of disruption (porosity) in the pleural layer, which are prone to rupture. Smoking may additionally lead to inflammation and obstruction of small airways, which account for the markedly increased risk of PSPs in smokers. Once air has stopped entering the pleural cavity, it is gradually reabsorbed.Tension pneumothorax occurs when the opening that allows air to enter the pleural space functions as a one-way valve, allowing more air to enter with every breath but none to escape. The body compensates by increasing the respiratory rate and tidal volume (size of each breath), worsening the problem. Unless corrected, hypoxia (decreased oxygen levels) and respiratory arrest eventually follow. Diagnosis
The symptoms of pneumothorax can be vague and inconclusive, especially in those with a small PSP; confirmation with medical imaging is usually required.
A blighted ovum is a pregnancy in which the embryo never develops or develops and is reabsorbed. In a normal pregnancy, an embryo would be visible on an ultrasound by six weeks after the womans last menstrual period. Anembryonic gestation is one of the causes of miscarriage of a pregnancy.A blighted ovum or anembryonic gestation is characterized by a normal-appearing gestational sac, but the absence of an embryo. It likely occurs as a result of early embryonic death with continued development of the trophoblast. When small, the sac cannot be distinguished from the early normal pregnancy, as there may be a yolk sac, though a fetal pole is not seen. For diagnosis, the sac must be of sufficient size that the absence of normal embryonic elements is established. The criteria depends on the type of ultrasound exam performed. A pregnancy is anembryonic if a transvaginal ultrasound reveals a sac with a mean gestational sac diameter (MGD) greater than 25 mm and no yolk sac, or an MGD >25 mm with no embryo. Transabdominal imaging without transvaginal scanning may be sufficient for diagnosing early pregnancy failure when
an embryo whose crown–rump length is 15 mm or more has no visible cardiac activity. See also
Ovum
Products of conception

References
External links

Blighted Ovum on WebMD
Anembryonic pregnancy on Radiopaedia.org
Johnson, MR; Riddle, AF; Sharma, V; Collins, WP; Nicolaides, KH; Grudzinskas, JG (January 1993). "Placental and ovarian hormones in anembryonic pregnancy". Human Reproduction (Oxford, England). 8 (1): 112–5. doi:10.1093/oxfordjournals.humrep.a137857. PMID 8458911.