| Abstract|| |
Fat necrosis in subcutaneous lipomas is very unusual and has been reported only occasionally. Literature regarding fine needle aspiration cytology of such a lesion is lacking although fat necrosis is well described in the breast. We came across a case of a large subcutaneous lipoma in the anterior abdominal wall with a well encapsulated area of fat necrosis. The aspiration smears showed an unusual picture which was misinterpreted as the fragments of the hydatid cyst wall. They were actually enlarged, nonnucleate, single adipocytes showing laminations, along with calcification and paucity of inflammation. Histopathology confirmed the diagnosis of fat necrosis within the lipoma. Such lesions can be mistaken on radiology for malignancy.
Keywords: Fat necrosis; fine needle aspiration cytology; subcutaneous lipoma.
|How to cite this article:|
Kavishwar VS, Rupani AB, Amarapurkar AD, Anchinmane V. Diagnostic problems in fine needle aspiration cytology of fat necrosis within a subcutaneous lipoma. J Cytol 2008;25:150-2
|How to cite this URL:|
Kavishwar VS, Rupani AB, Amarapurkar AD, Anchinmane V. Diagnostic problems in fine needle aspiration cytology of fat necrosis within a subcutaneous lipoma. J Cytol [serial online] 2008 [cited 2014 Oct 23];25:150-2. Available from: http://www.jcytol.org/text.asp?2008/25/4/150/50802
| Introduction|| |
Fat necrosis within a subcutaneous lipoma without any history of trauma is unusual with only very few cases described in literature.  Moreover, fine needle aspiration cytology findings have not been documented in such lesions although there are some histopathological descriptions. ,, We report here a case of well encapsulated fat necrosis within a subcutaneous anterior abdominal wall lipoma, where we faced diagnostic difficulty with the aspiration smears.
| Case Report|| |
A 32 year-old female came with the complaint of a swelling in the left side of the anterior abdominal wall which had been gradually increasing in size over the last two years. The clinical impression was that of a lipoma. There was no history of trauma or pain or any other significant symptom. On examination, the swelling was found to be 8 × 6 × 4 cm, soft, and within the anterior abdominal wall on the left side. On palpation, a well defined, nontender, mobile, firm, 1 cm lesion was felt within the above soft swelling at the medial edge.
Fine needle aspiration cytology (FNAC) was performed with a 22 gauge needle from the soft, large swelling as well as the small nodule. The former yielded a fatty aspirate whereas the latter yielded a scanty whitish aspirate. The slides were stained with Papanicolaou (Pap) and May-Grünwald-Giemsa (MGG) stains. Smears from the soft swelling showed clusters of mature adipocytes; suggesting a lipoma. Smears prepared from the firm lesion within the lipoma showed numerous, well-preserved, nonnucleate adipocytes that were markedly enlarged in size. They almost appeared membranous with their size being almost two to three times that of normal adipocytes. Most of them were seen singly [Figure 1] and many of them also showed parallel lamination under higher magnification [Figure 2]. The background showed fine, granular, proteinaceous material, calcific debris, and occasional macrophages [Figure 3]. The diagnosis of lipoma was made but the nonnucleated, enlarged adipocytes with membranous appearance and laminations along with background calcification were misinterpreted as being fragments of a laminated, hydatid cyst wall. The excisional biopsy sample was received in the Surgical Pathology department after one week and showed a well encapsulated lipoma 8 cm in diameter. A well capsulated, whitish-yellow, firm, 1.5 cm, partially cystic nodule with calcification was seen within the lipoma on the cut surface. The histopathology slides from the nodule showed sheets of similar enlarged, nonnucleate adipocytes with sparse inflammation and moderate calcification. There was also deposition of acellular pinkish material amidst the adipocytes [Figure 4]. A final diagnosis of lipoma with fat necrosis was given; FNAC slides were reviewed.
| Discussion|| |
Fat necrosis in subcutaneous lipoma is quite unusual with only a few cases being reported in the literature. , As in our case, most of them were within large superficial lipomas and no history of trauma may be available. Although cytological features of fat necrosis in organs such as the breast have been well documented, cytology of fat necrosis in subcutaneous lipomas has not, to the best of our knowledge, been described in the literature. 
The overall cytological appearance was different than what has been described in organs such as the breast where a dirty background with granular debris, fragments of adipose tissue with an abundance of foamy macrophages, multinucleate giant cells, and adipocytes with bubbly cytoplasm along with chronic inflammatory cells have been noted.  In our case, we did not note any such features. On reviewing the FNAC slides, we realized that the large necrotic adipocytes with focal laminations had appeared like the fragments of ecchinococcus parasitic cyst wall. Although parasitic infections and fat necrosis have not been described as differential diagnoses in literature, we faced this dilemma. However, the cytoplasmic membrane was preserved in most of the adipocytes and this feature can help us to distinguish the two lesions. As there were no reports describing the cytology of many such cases, we could not substantiate our findings. Also, we did not consider a clinical diagnosis of fat necrosis as the swelling was well circumscribed and there was no history of trauma.
Grossly, the area of the fat necrosis was well encapsulated and embedded within the lipoma specimen. Histologically, certain variants of fat necrosis such as membranous and nodular cystic fat necrosis have been described in the literature. ,, The nodular-cystic subtype is a posttraumatic, subcutaneous nodule which is nearly totally encapsulated and shows well preserved outlines of nonnucleate adipocytes histologically and cytologically, as seen in our case.  But this has not been described within subcutaneous lipomas. Another subtype, the membranous fat necrosis, rarely occurs within subcutaneous lipomas.  This type shows membranocytic change, mimicking a parasitic cuticle on histopathology, with numerous pigment-laden histiocytes. Cytology of this lesion has not been described. Also, pigment-laden macrophages were not seen in this case.
Generally, the larger subcutaneous lipomas may show fat necrosis as their size makes them more susceptible to trauma and ischemia.  Malignancy can be suspected on computed tomography (CT) scanning as these lipomas show lipomatous tumors with solid areas.  A CT scan, however, was not done in our case.
In conclusion, large lipomas should be palpated well for the presence of areas with different consistency and it should be noted that fat necrosis can occur in subcutaneous lipomas without any history of trauma. Also, fat necrosis in subcutaneous lipomas has a different appearance on cytology as compared to fat necrosis elsewhere, for example, in the breast.
| References|| |
|1.||López Soriano A, Tomasello A, Luburich P, Noel A. Fat Necrosis in a chest wall lipoma. Am J Roentgenol 2004;183:866. |
|2.||Hurt MA, Santa Cruz DJ. Nodular-cystic fat necrosis: A re-evaluation of the so-called mobile encapsulated lipoma. J Am Acad Dermatol 1989;21:493-8. [PUBMED] |
|3.||Poppiti RJ Jr, Margulies M, Cabello B, Rywlin AM. Membranous fat necrosis. Am J Surg Pathol 1986;10:62-9. [PUBMED] |
|4.||Ramdial PK, Madaree A, Singh B. Membranous fat necrosis in lipomas. Am J Surg Pathol 1997;21:841-6. [PUBMED] [FULLTEXT]|
|5.||Karin L. Breast. In: Orell SR, Sterrett GF, Whitaker D, editors. Fine needle aspiration cytology. 4th ed. Edinburgh: Churchill Livingstone; 2005. p. 165-227. |
Asha B Rupani
5, Sapna Hsg Society, Sector-4, Vashi, Navi Mumbai - 400 703
[Figure 1], [Figure 2], [Figure 3], [Figure 4]