Intraprostatic fat: does it exist?

Intraprostatic fat: does it exist?

CORRESPONDENCE 10. Gras E, Matias-Guiu X, Garcia A, et al: PCR analysis in the pathological diagnosis of Whipple’s disease: Emphasis on extraintestina...

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CORRESPONDENCE 10. Gras E, Matias-Guiu X, Garcia A, et al: PCR analysis in the pathological diagnosis of Whipple’s disease: Emphasis on extraintestinal involvement or atypical morphological features. J Pathol 188:318-321, 1999 11. von Herbay A, Ditton HJ, Maiwald M: Diagnostic application of a polymerase chain reaction assay for the Whipple’s disease bacterium to intestinal biopsies. Gastroenterology 110:1735-1743, 1996 12. Ehrbar HU, Bauerfeind P, Dutly F, et al: PCR-positive tests for Tropheryma whippelii in patients without Whipple’s disease. Lancet 353:2214, 1999

13. Maiwald M, von Herbay A, Persing DH, et al: Tropheryma whippelii DNA is rare in the intestinal mucosa of patients without other evidence of Whipple’s disease. Ann Intern Med 134:115-119, 2001 14. Southern JF, Moscicki RA, Magro C, et al: Lymphedema, lymphocytic myocarditis, and sarcoidlike granulomatosis. Manifestations of Whipple’s disease. JAMA 261:1467-1470, 1989 15. Walter R, Bachmann SP, Schaffner A, et al: Bone marrow involvement in Whipple’s disease: Rarely reported, but really rare? Br J Haematol 112:677679, 2001

CORRESPONDENCE Intraprostatic Fat: Does It Exist? To the Editor:—Invasion of fat is almost always a manifestation of extraprostatic spread by cancer.1 However, a published observation has indicated that rarely, significant expanses of fat may exist within the prostate, where its invasion by carcinoma would be misleading and might be considered evidence of extraprostatic spread.2 This published report was subsequently brought into question by evidence that the “fat areas” might represent defects or cavities in the section.3 To address this controversy, we dissected 150 prostates from consecutive autopsies of men over age 40 (mean and median age, 61 years) who died of diseases other than carcinoma of the prostate. The prostates were dissected free from the surrounding tissue and fixed uncut in 10% formalin for 5 days or longer. The glands were cut into 2 parts through a sagittal section passing through the middle of the organ. The ejaculatory ducts were easily visualized on each section plane because of the presence of yellow-brown pigment. The 2 halves were sectioned through the plane indicated by the presence of the ejaculatory duct. Sections of the posterolateral region corresponded to the portion of the gland lying posterior to the plane of section, and sections of the anterolateral region corresponded to the portion lying anterior to the plane of section. A step section method was used to cut the whole prostate in coronal planes in intervals of 0.3 to 0.5 cm. Blocks were

embedded in paraffin and cut at 6 ␮m, and 1 section from each block was stained with hematoxylin and eosin in a total of 5712 sections examined. Fat was considered to be located in 2 regions: beyond and amid or preceding the most peripheral acini. We preferred the latter location because the prostatic “capsule” is not a true capsule.4 The outer limit of the prostate corresponds to its own fibromuscular stroma. This limit may be sharp or imprecise due to bundles of fibromuscular stroma that penetrate and disappear into the periprostatic connective tissue stroma. For this study, the outer limit of the prostate was defined as the outer surface of the most peripheral acini of the gland. Fat was found amid and preceding the most peripheral acini of the gland in only 1 of 150 (0.66%) prostates examined. This fat, comprising a group of 6 adipose cells (Fig 1), was seen in only 1 of 45 sections of this prostate, corresponding to 1 of the total of 5712 sections (0.01%) examined. This section with fat was located in the anterolateral part of the gland. In all other sections fat was seen only beyond the most peripheral acini of the prostate. Prostatic adenocarcinoma detected in transrectal needle core biopsy is routinely evaluated by most pathologists with regard to length (extent) of cancer in the core, tumor grade, and evidence of extraprostatic spread into either seminal vesicles or periprostatic fat. These parameters correlate with the probability of surgical cure and may dictate therapeutic choices.2 There are 3 criteria for extraprostatic extension, depending on the site and composition of the extraprostatic tissue: (1) cancer in adipose tissue, (2) cancer in perineural spaces of the neurovascular bundles, and (3) cancer in anterior muscle.1 Our study demonstrated that intraprostatic fat is extremely rare. Invasion of fat in a needle biopsy specimen of the posterolateral region of the prostate appears to always be a manifestation of extraprostatic spread by cancer.

ATHANASE BILLIS, MD Department of Pathology State University of Campinas (Unicamp) Campinas, SP, Brazil 1. Bostwick DG, Montironi R: Evaluating radical prostatectomy specimens: Therapeutic and prognostic importance. Virchows Arch 430:1-16, 1997 2. Cohen RJ, Stables S: Intraprostatic fat [letter]. HUM PATHOL 29:424-425, 1998 3. Nopajaroonsri C: Intraprostatic fat [letter]. HUM PATHOL 29:887, 1998 4. Ayala AG, Ro JY, Babaian R, et al: The prostatic capsule: Does it exist? Its importance in the staging and treatment of prostatic carcinoma. Am J Surg Pathol 13:21-27, 1989

FIGURE 1. The focus of adipose tissue is located amidst and preceding the most peripheral prostatic acini. (Hematoxylin and eosin; original magnification ⫻ 83.)