Effects of extreme obliquity variations on the habitability of exoplanets.

We explore the impact of obliquity variations on planetary habitability in hypothetical systems with high mutual inclination. We show that large-amplitude, high-frequency obliquity oscillations on Earth-like exoplanets can suppress the ice-albedo feedback, increasing the outer edge of the habitable zone. We restricted our exploration to hypothetical systems consisting of a solar-mass star, an Earth-mass planet at 1 AU, and 1 or 2 larger planets. We verified that these systems are stable for 10(8) years with N-body simulations and calculated the obliquity variations induced by the orbital evolution of the Earth-mass planet and a torque from the host star. We ran a simplified energy balance model on the terrestrial planet to assess surface temperature and ice coverage on the planet's surface, and we calculated differences in the outer edge of the habitable zone for planets with rapid obliquity variations. For each hypothetical system, we calculated the outer edge of habitability for two conditions: (1) the full evolution of the planetary spin and orbit and (2) the eccentricity and obliquity fixed at their average values. We recovered previous results that higher values of fixed obliquity and eccentricity expand the habitable zone, but we also found that obliquity oscillations further expand habitable orbits in all cases. Terrestrial planets near the outer edge of the habitable zone may be more likely to support life in systems that induce rapid obliquity oscillations as opposed to fixed-spin planets. Such planets may be the easiest to directly characterize with space-borne telescopes.

Primary malignant melanoma of the urethra: a clinicopathologic analysis of 15 cases.

The clinical and pathologic features of 15 primary urethral melanomas occurring in patients (nine women and six men) age 44 to 96 years (mean age, 73 yrs) are described. In the men the tumor involved the distal urethra. In eight women it involved the distal urethra, usually the meatus; both the distal and proximal urethra were involved in one woman. The tumors were typically polypoid and ranged from 0.8 to 6 cm (mean, 2.6 cm) in maximum dimension. A vertical growth phase was present in all tumors, with a prominent nodular component in seven of them. A radial growth phase was seen in nine tumors. The depth of invasion ranged from 2 to 17 mm. The tumors had diffuse, nested, storiform, or mixed growth patterns. The neoplastic cells typically had abundant eosinophilic cytoplasm, large nuclei with prominent nucleoli, and brisk mitotic activity. Melanin pigment was seen in 12 tumors but was conspicuous in only six. At the time of diagnosis, 13 tumors were confined to the urethra and two patients had lymph node metastasis. Nine patients died of disease 13 to 56 months after initial diagnosis and treatment, and one patient had a local recurrence at 4 years and subsequently died of sepsis 1 year later. Three patients were alive and well at 11 months, 23 months, and 7 years. One patient died at the time of the initial operation, and one died of a ruptured aortic aneurysm at 3 years without evidence of melanoma at autopsy. Primary malignant melanomas of the urethra, one fifth of which are amelanotic, must be included in the differential diagnosis of a number of primary neoplasms that involve the urethra, including transitional cell carcinoma, sarcomatoid carcinoma, and sarcomas. Conventional prognostic factors, such as depth of invasion or tumor stage, do not seem to play as important a role in predicting survival as the mucosal location and the nodular growth present frequently in these tumors.

CO2 laser resurfacing of psoriatic plaques: a pilot study.

BACKGROUND AND OBJECTIVE: Laser resurfacing can precisely remove epidermis and papillary dermis, sites pivotal to the pathogenesis of psoriasis. Our objective was to determine the efficacy and safety of superficially ablating carbon dioxide (CO2) lasers for treating isolated, recalcitrant psoriatic plaques. MATERIALS AND METHODS: Twelve adult subjects with stable, plaque-type psoriasis were recruited. In six volunteers, the quadrants received different numbers of passes with a 60 microsec pulsed CO2 (Tru-Pulse) laser. In the remaining patients, one quadrant underwent curettage prior to resurfacing, the second resurfacing with a scanned continuous wave (Sharplan Silktouch) CO2 laser and the last curettage alone. RESULTS: Despite clinical and histological evidence of complete ablation of the epidermis and papillary dermis, most quadrants recurred within 8 weeks. Surprisingly, two patients showed no recurrence after 4 months. CONCLUSION: Ablation of the entire epidermis and papillary dermis with either pulsed or scanned CO2 lasers appears generally ineffective in treating recalcitrant psoriatic plaques, although the clearing seen in two patients suggests potentially successful future research directions.

Smooth-muscle hamartoma of the tunica dartos of the scrotum: report of a case.

Hamartomatous proliferations of genital smooth muscle are uncommon and may be easily overlooked if the normal microscopic appearance of the scrotal dartos is unfamiliar to the pathologist. We describe a hamartomatous proliferation of the scrotum in a 60-year-old patient in which incomplete knowledge of the regional histology caused initial problems in diagnosis. On histologic examination, the lesion consisted of an expansile, unencapsulated, relatively circumscribed proliferation of smooth muscle accompanied by muscular arterioles and prominent nerve branches embedded in a densely collagenized stroma. These features are dissimilar both clinically and histologically from all previous reported lesions at this site. We highlight the histologic differences between our case and genital leiomyomas, and the spectrum of hamartomatous smooth-muscle proliferations associated with a Becker nevus, and congenital and acquired smooth muscle hamartomas.

Epidermolytic hyperkeratosis in the lower female genital tract: an uncommon simulant of mucocutaneous papillomavirus infection--a report of two cases.

Two examples of epidermolytic hyperkeratosis (EH) involving the female genital tract are described. The first case, an isolated epidermolytic acanthoma, involved the vulva of a 75-year-old woman. The second case involved the vaginal wall of a 40-year-old woman who had similar lesions of the oral mucosa. EH is characterized by epidermal acanthosis, compact papillomatous hyperkeratosis, and dissolution of the suprabasilar epithelium, resulting in perinuclear clear zones. Granular keratohyalin clumping, hypergranulosis, and dyskeratosis resulting in intracellular eosinophilic globules ("cells within a cell" appearance) are additional distinctive findings. Because of the rarity of the lesion in the female genital tract, it may be confused with other lesions that more commonly affect this region. Correct recognition of EH may have significant clinical implications.