Poromas are rare, benign, cutaneous adnexal tumors. Cutaneous adnexal tumors are a group of skin tumors consisting of tissues that have differentiated (i.e. matured from stem cells) towards one or more of the four primary adnexal structures found in normal skin: hair follicles, sebaceous sweat glands, apocrine sweat glands, and eccrine sweat glands. Poromas are eccrine or apocrine sweat gland tumors derived from the cells in the terminal portion of these glands ducts. This part of the sweat gland duct is termed the acrosyringium and had led to grouping poromas in the acrospiroma class of skin tumors (syringofibroadenomas and syringoacanthomas are classified as acrospiromas). Here, poromas are regarded as distinct sweat gland tumors that differ from other sweat gland tumors by their characteristic clinical presentations, microscopic histopathology, and the genetic mutations that their neoplastic cells have recently been found to carry.As currently viewed, there are 4 poroma variants based on their predominant cell types and extent of the their tumor tissues presence in the epidermis and dermis: 1) Hidroacanthoma simplex poromas are confined to the epidermis, i.e. uppermost layer of the skin. 2) Dermal duct poromas are confined to the dermis, i.e. layer of skin between the epidermis and subcutaneous tissues. 3) Hidradenomas have recently been sub-classified into two groups; 95% are termed clear cell hidradenomas and have features suggesting that they derive from apocrine sweat glands while the remaining 5% are termed poroid hidradenomas and have features suggesting that they derive from eccrine sweat glands.
Ectromelia is a congenital condition where long bones are missing or underdeveloped. Examples include:

Amelia
Hemimelia
Phocomelia
Sirenomelia

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