We undertook a retrospective pathological study of 118 skin resection specimens from 101 patients with hidradenitis suppurativa. Follicular occlusion was identified in all the specimens, regardless of disease duration (1 month to 18 years), but was not noted in the axillary and inguinal skin of controls. We therefore regard follicular occlusion as an early and important feature in the pathogenesis of the disease. The presence of apoeccrine glands in axillary skin provided an in vivo model to directly observe the effects of follicular occlusion on follicle inflammation and apocrine gland destruction. In the majority of cases, active folliculitis was associated with apocrinitis and apocrine destruction, whereas apoeccrine glands, which drain directly on to the epidermal surface, appeared intact and non-inflamed. These observations provide direct evidence in an in vivo model that follicular occlusion by keratinous material, with subsequent active folliculitis and secondary destruction of the skin adnexae and subcutis, occur as an integral step in the pathogenesis of hidradenitis suppurativa.

Background-Colorectal crypts are clonal units in which somatic mutation of marker genes in stem cells leads to crypt restricted phenotypic conversion initially involving part of the crypt, later the whole crypt. Studies in mice show that the time taken for the great majority of mutated crypts to be completely converted, the clonal stabilisation time, is four weeks in the colon and 21 weeks in the ileum. Differences in the clonal stabilisation time between tissues and species are thought to reflect differences in stem cell organisation and crypt kinetics. Aim-To study the clonal stabilisation time in the human colorectum. Methods-Stem cell mutation can lead to crypt restricted loss of 0-acetylation of sialomucins in subjects heterozygous for 0-acetyltransferase gene activity. mPAS histochemistry was used to visualise and quantify crypts partially or wholly involved by the mutant phenotype in 21 informative cases who had undergone colectomy up to 34 years after radiotherapy. Results-Radiotherapy was followed by a considerable increase in the discordant crypt frequency that remained significantly increased for many years. The proportion of discordant crypts showing partial involvement was initially high but fell to normal levels about 12 months after irradiation. Conclusions

The clinicopathological features and immunohistochemical findings in 14 primary sarcomas of the lung collected over a 30-year-period are presented. This represents one sarcoma per 550 bronchogenic carcinomas undergoing resection in this centre. The study group comprised six leiomyosarcomas, five malignant peripheral nerve sheath tumours, two haemangiopericytomas and one epithelioid haemangioendothelioma. The majority of cases occurred in men (nine males: five females), with mean age at presentation of 54 years for men and 47 years for women. All leiomyosarcomas were seen in men, whereas malignant peripheral nerve sheath tumours showed no particular sex preponderance. Leiomyosarcomas were larger tumours than malignant peripheral nerve sheath tumours, mean tumour diameter 15 cm (range 10-25 cm) compared to 9.5 cm (7-15 cm), respectively. All leiomyosarcomas were situated intraparenchymally whereas two of the five malignant peripheral nerve sheath tumours were endobronchial in site. Extrathoracic metastates were seen at death in two of the six leiomyosarcomas but not in any of the malignant peripheral nerve sheath tumours. Overall survival was 28 months although for the leiomyosarcoma/malignant peripheral nerve sheath tumour group alone survival was 8 months. Tumour grading appeared to be a more useful prognostic factor than tumour site (endobronchial/parenchymal) or tumour size. Haemangiopericytoma and epithelioid haemangioendothelioma were associated with a more favourable prognosis.

Three patients with concurrent hidradenitis suppurativa and Crohn's disease are presented. The notable histological feature in each hidradenitis resection was the presence of numerous discrete epithelioid granulomas in areas of non-inflamed dermis. The purpose of the study was to determine the incidence of epithelioid granulomas in 101 hidradenitis patients and their significance in relation to systemic granulomatous disease. Discrete epithelioid granulomas were identified in 8% of the resections (10 patients). One patient had Crohn's disease and one other pulmonary sarcoidosis. Seven patients with granulomatous hidradenitis neither had nor developed any other disease during the 3-year follow-up period. Clinical review identified a further two patients with Crohn's disease but associated with non-granulomatous changes in the skin resections. Foreign body type granulomas were identified in 25% of the resections adjacent to ruptured hair follicles, sinus tracts or nearby degenerate sweat glands. The study shows that, although foreign body type granulomas are a common finding in hidradenitis, the presence of discrete epithelioid granulomas in the dermis away from the site of active inflammation is unusual and should alert the pathologist to the possibility of systemic granulomatous disease such as Crohn's disease or sarcoidosis.

Aim-To determine interobserver and intra-observer agreement in the assessment of cytological grade and intraduct necrosis in pure duct carcinoma in situ (DCIS) of the breast. Methods-Sixty unselected cases with illustrated diagnostic criteria were circulated to 19 practising histopathologists. Results-Overall agreement was moderate for cytological grade in three categories: 71% agreement; weighted ( w), 0.36; intraduct necrosis in three categories (absent, present, extensive): 76% agreement; w, 0.57; and the Van Nuys classification system: 73% agreement; w, 0.48. Agreement was no better among observers participating in the National External Quality Assurance Programme. Intraobserver agreement for cytological assessment (69.6% agreement; w, 0.52) and intraduct necrosis (68.3% agreement; w, 0.48) was moderate, suggesting that individual variation rather than precision of criteria contributes to the lack of agreement. Conclusions-Moderate agreement on observations can be achieved by nonspecialist pathologists, with better agreement on necrosis than cytological grade. There was evidence of consistent individual bias towards over or under scoring cytological grade, which could be corrected with adequate and prompt feedback. (J Clin Pathol 2000;53:596-602)