reticulated acanthoma with apocrine differentiation

RETICULATED ACANTHOMA WITH APOCRINE DIFFERENTIATION

From the chest of a 57 year old female.

This type of lesion was described by Requena et al^refas reticulated acanthoma with apocrine differentiation. The essence of the chapter was that this is a follicular tumor with distinctive architecture, and the apocrine differentiation is a manifestation of the fact that the apocrine sweat unit is part of the embryological pilosebaceous unit. They mention several related tumors, including those with sebaceous differentiation, and give appropriate references.

This type of horizontal growth pattern with fenestrated plates of follicular epithelium is seen in several settings. The 'tumor of the follicular infundibulum' has this architecture, and the epithelium in that lesion resembles that which is found in trichilemmomas. Follicular epithelium that is more primordial can sometimes be found in this pattern over dermatofibromas or in nevus sebaceus of Jadassohn.

If one considers all of the possible combinations and permutations of the various components of the pilosebaceous unit (epithelial and connective tissue) with varying degrees of differentiation, and with different architectural patterns, one is faced with a withering number of possibilities. Generic terms such as 'compound adnexal tumor', 'complex adnexal tumor', or 'combined adnexal tumor' supplemented with a notation as to architecture might be helpful in classifying some of these that contain ductal elements as well as follicular and/or sebaceous elements. The current case could be classified as 'fenestrated (or plaque type) combined adnexal tumor, follicular and ductal ' using such a scheme.

Scan power view. The fenestrated plate of acanthotic epithelium is visualized. Some of the epithelium is primordial, and some more closely resembles fully developed infundibular or outer root sheath epithelium.

Composite low power view. In addition to the epithelia described above, duct differentiation and a cystically malformed follicle are seen.

Medium power view. Small ductal lumina are illustrated in addition to the more elongate lumen.

High power view of above. Although apocrine differentiation is not cytologically convincing, such elongate ducts have been interpreted as being apocrine in this setting.

Another medium power view. Small lumina of ambiguous type are seen. The epithelium near the top is more 'mature' than that near the bottom. Peripheral palisading of the type that can be seen in trichilemmomas is present.

Reference:
1. Requena L, Kiryu H, Ackerman AB. Neoplasms with Apocrine Differentiation, 1st ed. Philadelphia: Lippincott-Raven, 1998.

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	Scan power view. The fenestrated plate of acanthotic epithelium is visualized. Some of the epithelium is primordial, and some more closely resembles fully developed infundibular or outer root sheath epithelium.
	Composite low power view. In addition to the epithelia described above, duct differentiation and a cystically malformed follicle are seen.
	Medium power view. Small ductal lumina are illustrated in addition to the more elongate lumen.
	High power view of above. Although apocrine differentiation is not cytologically convincing, such elongate ducts have been interpreted as being apocrine in this setting.
	Another medium power view. Small lumina of ambiguous type are seen. The epithelium near the top is more 'mature' than that near the bottom. Peripheral palisading of the type that can be seen in trichilemmomas is present.