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The microanatomy of the subcutaneous layer is supplied by arteries and arterioles in the ______ portion and venules and veins in the _______ portion.

A) Centrilobular, Septal

B) Septal, Centrilobular

C) Septal, Septal

D) Centrilobular, Centrilobular

The correct answer is A.

The subcutaneous tissue consists of depot fat sandwiched between the reticular dermis above and the superficial fascia beneath. Adipose tissue is organized into two compartments: (1) discrete round or ovoid lobules composed of confluent aggregates of the clear-appearing fat cells and (2) fibrous trabeculae (or septa) that form a meshwork separating the individual fat lobules. The fibrous septa are continuous with collagen of the reticular dermis and the superficial fascia and contain all the blood vessels, lymphatics, and nerves of the subcutaneous fat. In one sense, the fibrous septa simply serve as scaffolding for vascular and nerve plexi traversing the subcutis from deeper tissue to supply the skin (Table 5-1A). Thus, inflammatory conditions affecting the fat often involve the reticular dermis and fascia, and vice versa. Arterial vessels in the fat are small to medium in size and are categorized as muscular arteries. Thus, it is not possible to develop large-vessel arteritis in the subcutaneous fat but rather an arteritis affecting vessels of the caliber noted in polyarteritis nodosa.

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Table 5-1A. Evaluation of Panniculitis
  1. Excisional wedge biopsy is necessary for adequate sampling.

  2. Punch biopsies are to be discouraged and may be misleading.

  3. Biopsy is an active rather than a late-stage lesion.

  4. Special stains for infectious organisms include Gram, acid-fast, fungal, Warthin-Starry, Fite-Faraco.

  5. Examine specimen under polarized light for foreign material.

  6. Laboratory investigation includes cultures and other techniques, such as immunostaining and polymerase chain reaction, for infection; serologic testing for syphilis, borreliosis, connective tissue disease, vasculitis, alpha-antitrypsin deficiency, calcium, phosphorus, oxalate, coagulopathy, lipase, and amylase.

  7. Directed clinical history for isolated lesion (eg, ruptured cyst), trauma, factitial causes, psychiatric illness, drug abuse, cold exposure, recent medications, systemic disease, eg, vasculitis, connective tissue disease, sarcoidosis, infections, and malignancy.

Each fat lobule is vascularized by a single arteriole and, in effect, is an end organ with no collateral blood supply. There are no lymphatics within the lobules. Any interruption to this arterial supply will eventuate in ischemia or infarction of the fat lobule depending on the speed with which vascular compromise develops (Table 5-1B). The individual fat cells are supplied by arterial capillaries, which drain to venous capillaries and venules at the peripheries of the fat lobules. Based on these vascular patterns, in very general terms pathologic processes affecting arterial vessels may result in a “lobular” pattern of panniculitis versus a “septal” pattern ...

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