Angiomyxolipoma: a rare variant over the forehead

Abstract

Lipoma is a common benign mesenchymal tumour. However, angiomyxolipoma (AML) is one of its rarer variants. It was first described by Mai et al in 1996 in the lipomatous lesions having mature adipocytes in a myxoid background with rich vascular network. We present the case of a 21 year-old man with recurrent forehead swelling diagnosed as AML on microscopy. It is important to document this rare variant to add to the limited literature and to aid in differentiating it from its malignant counterpart. Moreover, as our case presented with recurrence within a short period of time, a precise diagnosis and documentation of recurrence is essential as it is reportedly the first case with recurrence among the 21 cases of AMLs previously published.

Background

Lipoma is one of the most common benign mesenchymal tumours with numerous variants, among which angiomyxolipoma (AML) is very rare. We present a case of a 21-year-old man with a recurrent subcutaneous forehead swelling having histological features of AML, making it the 22nd documented case to date.^{1 2}

Case presentation

A 21-year-old man presented with a swelling over the forehead 6 months ago, which was excised elsewhere. According to the patient, the biopsy was reported as lipoma. However, the swelling relapsed at the same site after 1 month (figure 1) and the patient was admitted in our institute for an excisional biopsy.

Figure 1.

Photograph showing a swelling over the forehead.

Investigations

The excised soft tissue was globular and yellow–white measuring 3×2.5×1 cm. The cut surface was well-circumscribed, homogeneous, myxoid and yellow–white (figure 2). Microscopic examination showed an encapsulated neoplasm comprised of varying proportions of mature adipocytes, blood vessels and myxoid to collagenised matrix. Adipocytic lobules were dispersed in a background of myxoid matrix and ropy collagen bundles with a shredded carrot appearance. The stromal cells were stellated to spindled with round to oval nucleus and moderate amounts of cytoplasm. Numerous small and mildly congested and thick walled blood vessels were seen. Interspersed mast cells and eosinophils were seen. Atypical mitoses, lipoblasts and necrosis were not noted. There was no evidence of malignancy (figures 3–5). The Alcian blue staining highlighted the myxoid matrix (figure 6).

Figure 2.

Photograph showing the cut section of the gross specimen.

Figure 3.

Photomicrograph showing a lesion comprised of mature adipocytes in a background of myxoid stroma and blood vessels. (H&E, 40×).

Figure 4.

Photomicrograph showing a lesion comprised of mature adipocytes in a background of myxoid stroma and blood vessels.(H&E, 100×).

Figure 5.

Photomicrograph showing a lesion comprised of mature adipocytes in a background of myxoid stroma and blood vessels. (H&E, 100×).

Figure 6.

Photomicrograph showing myxoid matrix highlighted by Alcian blue (Alcian blue, 400×).

On immunohistochemistry (IHC), the mature adipocytes were immunoreactive for S100P and the stromal cells were negative for CD34(figures 7 and 8). The rich vascular network was highlighted by CD31 and the Ki67 labelling index was less than 1% (figures 9 and 10).

Figure 7.

Photomicrograph showing a lesion comprised of mature adipocytes immunoreactive for S100P but not the myxoid stroma (immunohistochemistry, S100P).

Figure 8.

Photomicrograph of stromal cells not showing immune-reactivity to CD34 (immunohistochemistry, CD34).

Figure 9.

Photomicrograph showing a lesion with rich vascular network highlighted by CD31 (immunohistochemistry, CD31).

Figure 10.

Photomicrograph showing a lesion having low proliferative labelling index (immunohistochemistry, Ki67).

A diagnosis of benign AML was rendered and the patient has been kept on follow-up owing to a history of a recurrent swelling.

Outcome and follow-up

Post-operative period was uneventful and patient is doing well.

Discussion

AML was first described by Mai et al² as an asymptomatic, solitary well-demarcated mass having mature adipose tissue with a myxoid background, spindle cells and numerous proliferating blood vessels. It a very rare variant of lipomatous lesions with very few cited occurrences on the scalp.^{3 4}

The mean age of presentation ranges from 4 to 70 years with a slight male preponderance.¹

The lesion is usually painless and solitary but incidences of multiple and painful lesions have been reported.^5–7 Our case was a 21-year-old man presenting with a recurrent soft to firm, painless swelling over the forehead.

On ultrasound, the lesions appear well-demarcated with mixed echogenicity and areas of increased vascularity. Likewise, on CT scan and MRI the lesion gives a heterogeneous signal intensity most likely due to a mixture of vascular, adipose and myxoid components.^{8 9}

The gross appearance of the lesions’ cut surface is yellowish and myxoid.¹ On microscopic examination, there is an admixture of mature adipose tissue, myxoid matrix with stellate cells and rich vascular network in a background of mild mixed inflammatory infiltrate.

The major differential diagnoses of AML are spindle cell lipoma/pleomorphic lipoma (SPL), chondroid lipoma, myxolipoma, angiolipoma, dendritic fibroangiolipoma, myolipoma, angiomyolipoma, superficial angiomyxoma, angiomyofibroblastoma, cellular angiofibroma, lipoblastoma, low-grade myxofibrosarcoma and myxoid liposarcoma.^{1 10 11} A non-lipomatous differential diagnosis of myxoid neurofibroma is also considered. Another differential diagnosis which needs to be considered is myxoid fibrolipoma which although common in head and neck areas in men, can be differentiated from AML in lacking rich vascular network and also possessing dense fibrous stroma.^{3 4 12}

Hence, its diagnosis can be established on the basis of microscopy, aided by IHC.

Histological examination of SPLs show pleomorphic stromal cells and poorer vascularity in contrast to the benign stellate cells and rich vascular network of AMLs. Chondroid lipomas and myxolipomas have chondroid and myxoid matrix devoid of rich vascular networks. Angiolipoma and myolipoma lack one of the three components of AML and angiomyolipoma has HMB45 positive smooth muscle bundles.¹⁰ Superficial angiomyxomas are aggressive and they are poorly circumscribed with presence of neutrophils and epithelial structures.¹⁰

AMLs differ from low-grade myxofibrosarcoma in lacking cellular pleomorphism, nuclear atypia, hypercellularity and hypervascularity.¹³ Likewise, the lack of lipoblasts, chicken wire capillary network, necrosis and presence of low Ki67 labelling index distinguishes them from myxoid liposarcoma and lipoblastoma.¹³ Myxoid neurofibromas can be excluded on the basis of negative expression of S100P by the stromal cells.

On IHC, the mature adipocytic component of AML is immunoreactive for S100P which is negative in the stromal cells. The rich vascular network is positive for CD31 and CD34. Out of the 21 reported cases, 15 cases showed CD34 positivity in the stromal cells. However, Hattori and Billings et al have observed that negativity of stromal cells for CD34 rules out the possibility of SPLs hence indicating that AMLs have CD34-negative stromal cells.^{14 15} All cases of AML reported to date had Ki67 labelling index of <5% and were found to be negative for HMB45.¹

Our case concurred with the literature in having similar gross, microscopic and IHC findings. The mature adipocytes were immune positive for S100P and negative for CD34. The rich vascular network was positive for CD34 and Ki67 labelling index was <1%.

The established treatment is surgical excision with excellent prognosis and rare incidence of recurrence.

Learning points.

• Angiomyxolipoma (AML) is a rare variant of lipoma with cases reported mostly in the extremities.

• The morphological features of this lesion carries a varied differential diagnoses including malignant counterparts which may prove fatal if misdiagnosed.

• As our case presented at a rare site and had a history of recurrence, it warranted a mention in the limited stock of literature available for AMLs.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).