Disorders of the panniculus adiposus

Anatomy and histology of normal subcutaneous fat, necrosis of adipocytes, and classification of the panniculitides

The panniculitides comprise a group of heterogeneous inflammatory diseases that involve the subcutaneous fat. Histopathologic study is required for the specific diagnosis of these disorders, because different panniculitides usually show the same clinical appearance, which consists of erythematous nodules on the lower extremities. The histopathologic study of panniculitis is difficult, however, because of an inadequate clinicopathologic correlation and the changing evolutive nature of the lesions. Some cutaneous lymphomas may simulate panniculitis, both from clinical and histopathologic points of view, and for that reason are included in this article despite the fact that they are not inflammatory processes but authentic lymphocytic neoplasms involving subcutaneous tissue.

Diagnosis: erythema nodosum or not?

Erythema nodosum is the final common pathway to a myriad of insults and is thought to be a hypersensitivity reaction centered in the subcutis. To recognize the histological spectrum of erythema nodosum, one must be aware of the morphologic chronology of the disease (early, fully developed, late) and its clinical variants (erythema nodosum migrans). This article reviews the range of changes that can be seen in this prototype of a septal panniculitis and describes the diversity that may be accepted in the diagnosis. Differential diagnoses at each stage of disease development are discussed. The criteria elaborated should assist the pathologist in answering the clinician's query, "Erythema nodosum, or not?"

Panniculitis: recent developments and observations

Dermatopathologists rarely greet a biopsy of panniculitis with total confidence that a specific, definitive diagnosis will be rendered. As with many other areas in dermatopathology, our understanding of the pathogenesis of many forms of panniculitis is incomplete. This article examines a subset of panniculitis primarily from a pathogenetic standpoint, with the intention of providing a differential diagnosis for those cases in which ischemic changes are seen in the subcutis. The diverse group of conditions evoked by this approach also shares the distinction of having been the focus of nosologic and causative controversy, both historically and currently. In particular, stasis-associated sclerosing panniculitis, vascular calcification-cutaneous necrosis syndrome (calciphylaxis), oxalosis, and nodular vasculitis-erythema induratum are examined in depth. Erythema nodosum and variants, other granulomatous panniculitides, and panniculitides showing cytophagocytosis are also discussed with current perspectives.

Possible origin of pancreatic fat necrosis as a septal panniculitis

We describe pancreatic subcutaneous fat necrosis in a man with alcoholism and pancreatitis. The initial specimen, from a 2-day-old lesion, showed a septal inflammatory infiltrate in the subcutis. A second specimen, from a 5-day-old lesion, showed the lobular pattern of enzymatic fat necrosis diagnostic for pancreatic panniculitis. We suggest that the histologic appearance of subcutaneous pancreatic fat necrosis evolves from an early septal reaction to a fully developed lobular panniculitis.

Primary extracellular ceroid type lipopigment. A histochemical and ultrastructural study

An extracellular ceroid-type (ECC) lipopigment which appears histologically as wavy hyaline membranes or, less frequently, as an amorphous solid or broadly reticulated mass is described. Its ultrastructure is either amorphous or membranous and consists either of simple linear membrane-like aggregates or elaborated trilaminar membranes. The histochemical profile is, as in histiocytic intracellular ceroid, dominated by autofluorescence, strong hydrophobicity, acid and extraction resistance. Staining for aromatic acid residues and periodic acid-Schiff positivity are strong but variable. Lectin receptors are either absent or sparse. The pigment is found solely within the lipid rich tissue debris, bound to processes marked by necrosis of adipose or steatosed tissues and interpreted as originating de novo extracellularly from liquid unsaturated lipids under the influence of local enzymatic and nonenzymatic lipid oxidation catalysts. A hitherto unknown form of extracellular ceroid is the so-called membranocystic lesion found in Nasu-Hakola's disease, in several other conditions and in annular ceroid in human atheromas.

Infection-induced panniculitis

We evaluated the histopathologic findings in 15 cases of panniculitis due to infection. Organisms were identified by special staining in 14 cases, and in 6 of these the etiologic agent was confirmed by culture studies. In one additional case, lesional culture was positive despite negative special staining. Eight cases were caused by gram positive or gram negative bacteria, 2 by atypical mycobacteria, 2 by Nocardia, and 3 by fungi (Candida and Fusarium species). Most patients had conditions or were receiving therapies predisposing to immunosuppression, but at least 2 individuals had no other major medical problems. There were some variability in microscopic findings and overlap with established forms of panniculitis; 3 cases (2 due to bacteria and 1 to Fusarium) resembled acute, "neutrophilic" erythema nodosum, and evidence of vasculitis was seen in septicemias due to Pseudomonas, Nocardia, and Fusarium. Nevertheless, several distinctive features associated with infectious panniculitis of diverse etiologies included: epidermal alterations such as acanthosis and parakeratosis; dermal edema with a diffuse or perivascular neutrophilic infiltrate; and mixed septal-lobular panniculitis with neutrophilic infiltration, vascular proliferation and hemorrhage, and necrosis. Infection should be suspected in virtually any case of panniculitis, particularly when occurring in an immunosuppressed patients, but the microscopic features enumerated above should arouse particular suspicion of an infectious process.

The fate of hypodermis after liposuction surgery

Liposuction surgery can be viewed as a trauma to the hypodermis. With histologic, morphometric, and autoradiographic examination and the use of tritiated thymidine, uridine, and proline, we have studied the fate of adipose tissue at various intervals after liposuction; however, we have never seen a reparative proliferation of the residual lipocytes. Moreover, the metabolic activity of adipocytes apparently is not increased. Inflammatory reaction is minimal in the early weeks, but fibrosis takes place in some lobules of the hypodermis. Our data support the view that liposuction has a long-term effect on the structure of the hypodermis, without any stimulation in the proliferative and biosynthetic activity of residual adipocytes.

Visceral brown fat necrosis in postperinatal mortality

Fat necrosis was present in 22 of 400 cases of consecutive postperinatal mortalities investigated to assess the presence and pattern of deep fat necrosis. In just over 50% of the cases of fat necrosis the cause of death was categorised as sudden infant death syndrome, which also showed more severe degrees of necrosis. The mechanism of necrosis may be vascular hypoperfusion, possibly related to shock, and brown adipose tissue, on account of its high metabolic activity and rich capillary plexus, may be particularly vulnerable to infarction. The occurrence of fat necrosis in association with other causes of death did not provide any definite clue as to the nature of the alleged shock.

The histopathology of localized lipoatrophy

We studied 11 patients with the clinical diagnosis of lipoatrophy and found two histopathological subsets. Six patients presented with a distinctive picture, which we termed 'involutional' fat, consisting of lobules of small lipocytes embedded in hyaline connective tissue with numerous capillaries. Five of these six patients had a single lesion, usually of the upper arm. Serological studies were normal, and direct immunofluorescence, performed in three cases, showed immunoreactants in the blood vessels in only one. The four patients with inflammation of the fat had multiple areas of localized lipoatrophy. Three had biopsies for direct immunofluorescence and all three showed immunoreactants involving the basement membrane zone (two cases) or blood vessels (one case); and three had serological abnormalities. We suggest that the involutional histopathological pattern is a distinctive subset of localized lipoatrophy.

The histopathology of lupus erythematosus panniculitis

Lupus erythematosus panniculitis is a clinical variant of lupus erythematosus in which the main pathologic process involves the deep corium and subcutaneous tissue. We reviewed twenty-nine cases of lupus panniculitis, as well as the cases previously reported in the literature. The histopathologic changes in lupus panniculitis are characterized by a lymphocytic panniculitis, hyaline degeneration of the fat, hyaline papillary bodies, and lymphoid nodular structures in the lower dermis and subcutaneous tissue. Direct immunofluorescence can be important in supplementing the histopathologic study of lupus panniculitis. Lesions of discoid lupus erythematosus are seen in 21% of cases. When this disorder exists in the absence of other typical cutaneous or systemic lesions, the diagnosis of lupus erythematosus has been questioned. We believe that the histopathologic findings of this entity are alone sufficient for a diagnosis of lupus panniculitis, even in the absence of cutaneous or systemic lesions.

Weber--Christian syndrome in infancy

A review of Weber-Christian syndrome in infancy is presented along with the report of two cases. Both infants had low serum properdin levels, and one patient showed remissions of his disease when he was T-lymphocytopenic. This suggests that the T-lymphocyte may have an important role in the pathogenesis of Weber--Christian syndrome.