Nodular-cystic fat necrosis

Nodular cystic fat necrosis: a distinctive rare soft-tissue mass

We report the case of a 34-year-old female who was evaluated for a right lower extremity soft-tissue mass, found to be a large cystic lesion bound by fibrous tissue containing innumerable, freely mobile nodules of fat. Her presentation suggested the diagnosis of nodular cystic fat necrosis (NCFN), a rare entity that likely represents a morphological subset of fat necrosis potentially caused by vascular insufficiency secondary to local trauma. Her lesion was best visualized using MRI, which revealed characteristic imaging features of NCFN including nodular lipid-signal foci that suppress on fat-saturated sequences, intralesional fluid with high signal intensity on T2-weighted imaging, and a contrast-enhancing outer capsule with low signal intensity on T1-weighted imaging. Ultrasound imaging offered the advantage of showing mobile hyperechogenic foci within the anechoic cystic structure, and the lesion was otherwise visualized on radiography as a nonspecific soft-tissue radiopacity. She was managed with complete surgical excision with pathologic evaluation demonstrating, similar to the radiologic features, innumerable free-floating, 1-5 mm, smooth, nearly uniform spherical nodules of mature fat with widespread necrosis contained within a thick fibrous pseudocapsule. Follow-up imaging revealed no evidence of remaining or recurrent disease on postoperative follow-up MRI. The differential diagnosis includes lipoma with fat necrosis, lipoma variant, atypical lipomatous tumor, and a Morel-Lavallée lesion. There is overlap in the imaging features between fat necrosis and both benign and malignant adipocytic tumors, occasionally making this distinction based solely on imaging findings challenging. To our knowledge, this is the largest example of NCFN ever reported.

Subcutaneous, abdominal, and thoracic encapsulated fat necrosis in bowhead whales Balaena mysticetus from Alaska, USA

We describe a case series of encapsulated fat necrosis with subcutaneous, abdominal, and thoracic locations in 7 subsistence-harvested bowhead whales Balaena mysticetus. Masses had a variably-dense fibrous capsule surrounding necrotic adipocytes and calcium salts (saponification). One animal also had prior concussive injury, pleural fibrosis, and hepatic lipoma; the other animals had no significant findings. The described condition is uncommon in bowhead whales, with 7/575 (1.2%) observed from 1996 to 2015. The exact mechanisms of development of encapsulated fat necrosis in bowhead whales remain to be determined. Encapsulated fat necrosis has been reported in other baleen whales, humans, and cows. It is usually an incidental finding during post-mortem examination that needs to be differentiated from neoplastic and inflammatory lesions, as the latter may have public health implications. Assessment of further cases in bowhead whales and other baleen whales is warranted to better understand their pathogenesis.

Nodular cystic fat necrosis with calcification in a patient with juvenile dermatomyositis

Nodular cystic fat necrosis is a rare, benign form of encapsulated fat necrosis with distinct histology, characterized by cystic fat necrosis with lipomembranous changes and, in later stages, calcification. We report the case of a 7-year-old child with juvenile dermatomyositis who presented with three asymptomatic, firm, mobile nodules on the arms and neck. Histology was consistent with nodular cystic fat necrosis with prominent calcification. This is an unusual presentation of this entity because it has never been previously reported in association with juvenile dermatomyositis.

Posttraumatic fat necrosis presenting as prepatellar loose bodies in an adolescent football player

A 16-year-old high school football player presented with 4 months of anterior knee pain and small, mobile, prepatellar "lumps" after falling onto an opponent's cleat. He reported knee pain primarily during knee flexion and direct pressure during squatting and kneeling. Knee radiographs were unremarkable. Ultrasonography revealed multiple, freely mobile, subcutaneous nodules of variable size and echogenicity in the prepatellar region. Analysis of magnetic resonance imaging suggested possible fat necrosis but was nondiagnostic. The patient opted for surgical exploration, at which time multiple, opalescent subcutaneous nodules were removed. Pathology was consistent with encapsulated fat necrosis. After surgery, his symptoms resolved, and he returned to sports without restrictions.

Encapsulated fat necrosis mimicking subcutaneous liposarcoma: radiologic findings on MR, PET-CT, and US imaging

We present a case of a subcutaneous encapsulated fat necrosis of the upper extremity that mimicked subcutaneous liposarcoma because of heterogeneous signal intensity, its relatively large size, and pronounced enhancement on magnetic resonance imaging (MRI). For this case, we present the radiologic findings including MRI, positron emission tomography-computed tomography (PET-CT), ultrasonography, and radiography. We emphasize the imaging features of this lesion, which has a fibrous capsule and briefly discuss its nomenclature and pathophysiology.

Mobile Encapsulated Adipose Tissue (MEAT) of Cows and Humans

Mobile encapsulated adipose tissue can be found in both the subcutis and peritoneal cavity. The cutaneous lesions are more common and better described; they are usually designated as “mobile encapsulated lipoma” or “nodular-cystic fat necrosis.” The clinical name of abacus tumor describes best the small marble-like nodules that often can be moved freely through the subcutaneous tissue planes. Histopathologically, the nodules are composed of a dense fibrous capsule surrounding fat that may show varying degrees of necrosis, calcification, and lipomembranous changes. The peritoneal nodules are thought to originate from detached epiploic appendices. They are described occasionally in humans but more commonly in cows. Because these bovine mobile peritoneal bodies are clinically and histopathologically identical to the nodules in human subcutaneous tissue, the authors suggest that one can better understand both processes by comparing them. Because the lesions are reactive, not neoplastic, and necrosis is not an invariable feature, the authors suggest the neutral designation of mobile encapsulated adipose tissue.

Mobile submuscular mass resembling a hard-boiled egg: case report

A 68-year-old woman had a rare mobile mass on her back. The mass was similar to encapsulated fat necrosis except for its unusual stalked appearance, large size, and high degree of mobility underneath the anterior serratus muscle on the back. Based on previous descriptions of encapsulated fat necrosis, the clinical presentation of the mass might be regarded as an extreme example of this rare condition.

Subcutaneous pseudomembranous fat necrosis: new observations

BACKGROUND

Pseudomembranous fat necrosis is a peculiar manifestation of necrosis of adipose tissue characterized by formation of pseudocystic cavities lined by crenulated membranes. The underlying mechanism for the formation of pseudomembranes is unknown and numerous hypotheses have been proposed. Despite divergent interpretations, most authors consider necrotic fat cells to be the anatomic substrate for the formation of pseudomembranes.

METHODS

A total of 341 panniculitides were reviewed for the presence of pseudomembranous fat necrosis. The specific diagnoses were established after correlation of all available clinical and laboratory data with the histopathology. Special attention was given to the time in the evolution of the disease when the biopsy was taken. Additional immunohistochemical studies were performed in 12 cases.

RESULTS

Thirty of 341 cases of different types of panniculitides were found to show pseudomembranous fat necrosis, namely: 10 of 15 cases of sclerosing panniculitis (lipodermatosclerosis), 6 of 95 cases of erythema nodosum, 7 of 34 cases of traumatic panniculitis, 1 of 7 cases of lupus panniculitis, 1 of 20 cases of erythema induratum Bazin (nodular vasculitis), 1 of 9 cases of necrobiosis lipoidica, 1 of 4 cases of sclerotic lipogranuloma, 1 of 9 cases of infectious panniculitis (erysipelas), 1 of 2 cases of pancreatic panniculitis, and 1 of 4 cases of subcutaneous sarcoidosis. Pseudomembranous fat necrosis labelled strongly for the histiocytic markers CD68 and lysozyme.

CONCLUSIONS

Our series provides data suggesting that pseudomembranous fat necrosis represents a dynamic process that varies according to the evolution of the lesion at the time of the biopsy. In biopsies taken from early foci of panniculitides pseudomembranes show vescicular or picnotic nuclei. Later, pseudomembranes retain their crenulated appearance but lack nuclear elements. Furthermore, we present histopathologic, histochemical, and immunohistochemical evidence that pseudomembranous fat necrosis results from the interaction of residual products of disintegrated fat cells and macrophages. Histiocytic markers such as CD68 and lysozyme may be used as reliable tools in order to detect pseudomembranes in panniculitides.

Encapsulated fat necrosis: a case of 'thigh mouse'

Encapsulated fat necrosis is a rare condition with clinical features that closely resemble a lipoma. The aetiology and pathogenesis are not fully understood but the condition has a distinctive histological appearance. We describe a case of encapsulated fat necrosis that exhibited unusual mobility. The literature is also reviewed.

Panniculitis. Part II. Mostly lobular panniculitis

The second part of our review of panniculitis summarizes the clinicopathologic features of the mostly lobular panniculitides. Erythema induratum of Bazin (nodular vasculitis) represents the most common variant of lobular panniculitis with vasculitis, although controversy persists about the nature of the involved vessels. Mostly lobular panniculitides without vasculitis comprise a series of disparate disorders. These include sclerosing panniculitis that results from chronic venous insufficiency of the lower extremities; panniculitis with calcification of the vessel walls such as calciphylaxis and oxalosis; and inflammatory diseases with crystals within the adipocytes such as sclerema neonatorum, subcutaneous fat necrosis of the newborn, and poststeroid panniculitis. Connective tissue diseases, such as systemic lupus erythematosus and dermatomyositis, pancreatic diseases, and alpha(1)-antitrypsin deficiency may also show a mostly lobular panniculitis with characteristic histopathologic features. Lobular panniculitis may also be an expression of infections, trauma, or factitial causes involving the subcutaneous fat. Lipoatrophy refers to a loss of subcutaneous fat due to a previous inflammatory process involving the subcutis, and it may be the late-stage lesion of several types of panniculitis. In contrast, lipodystrophy means an absence of subcutaneous fat with no evidence of inflammation and often the process is associated with endocrinologic, metabolic, or autoimmune diseases. Finally, cytophagic histiocytic panniculitis is the term that has been used to describe two different processes: one is inflammatory, a lobular panniculitis, and the other one is neoplastic, a subcutaneous T-cell lymphoma. The only common feature of these two different processes is the presence of cytophagocytosis in the lesions. (J Am Acad Dermatol 2001;45:325-61.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should be familiar with the pathogenesis, clinical manifestations, histopathologic findings, and treatment options for the most frequent variants of the lobular panniculitides.

Synovial metaplasia in lipoma

We present a unique case of a lipoma with widespread synovial metaplasia. A 52-year-old woman had a recurrence 1 year after excision of a subcutaneous lipoma of the neck. Histologically, the primary tumor was an ordinary lipoma. The recurrent tumor was a myxoid lipoma with synovial metaplasia. The synovial metaplastic process manifested as labyrinthlike clefts, which were lined by one or more synovial-like cell layers. Ultrastructurally, the synovial metaplastic cell had secretory, phagocytic, and fibroblastlike features.

Encapsulated fat necrosis in a patient with Ehlers-Danlos syndrome

Mobile encapsulated lipoma, first described by Sahl in 1978 (1), is characterized by its great mobility within subcutaneous adipose tissue and presentation with or without tenderness when the nodules are manipulated. This lipoma's histopathology is very characteristic; i.e., it consists of mature viable or degenerative lipocytes encapsulated by fibrous tissue. We report a case of this so-called mobile encapsulated lipoma involving a patient with Ehlers-Danlos syndrome. This case is the first report of mobile encapsulated lipoma in a patient with a disease of this type. We discuss its pathogenesis and the nomenclature for these lesions.

Lipomembranous changes in nodular-cystic fat necrosis

Three cases of nodular-cystic fat necrosis presenting with focal lipomembranous changes are reported. The lesions consisted of solitary (cases 1 and 3) or multiple (case 2) subcutaneous nodules on the upper (case 1) or lower (cases 2 and 3) extremities which had evolved over weeks to years. At surgical excision, solitary or multiple, freely mobile nodules within a cystic cavity were observed. Histologically, encapsulated fat nodules showing variable amounts of necrosis without marked inflammatory changes were present. Focal lipomembranous changes were observed in some nodules. Our observations seem to support the concept that lipomembranous changes are nonspecific and uncommon patterns of fat necrosis caused by a wide variety of local or systemic events that may cause a compromise in the blood supply of the subcutaneous tissue.

Nodular cystic fat necrosis in a patient with erythema nodosum

Nodular cystic fat necrosis shows a distinctive spectrum of clinical and histological features. Most of the lesions are mobile subcutaneous nodules in regions vulnerable to trauma, such as the elbows, knees, and shins. There have been no reports of an association with other conditions. The histology is characterized by encapsulated fat necrosis in which multiple, non-viable adipocytes are surrounded by condensed fibrous tissue. We report a case of early stage nodular cystic fat necrosis associated with erythema nodosum.