Meningothelial hamartoma of the scalp in a 78-year-old man

ARTICLE

ejd.2010.1234

Auteur(s) : Min LI¹, Shinichi ANSAI¹, Takashi UENO² limin@nms.ac.jp, Seiji KAWANA¹

¹ Nippon Medical School Department of Dermatology, Sendagi 1-1-5,Bunkyo-ku, 113-8602 Tokyo, Japan

² Nippon Medical School Musashikosugi Hospital, Kawasaki, Japan

Meningothelial hamartoma (MH) was first described by Suster and Rosai [1] as a hamartoma of the scalp showing a mixture of fat, blood vessels, nerves and ectopic meningothelial cells. Similar cases have probably been described as rudimentary meningocele, sequestrated meningocele or cutaneous meningioma [2, 3]. MH is congenital and it is believed to be a result of a developmental defect related to displaced ectopic meningothelial remnants at this site [1]. It has also been postulated that it represents a form of meningocele with an obliterated intracranial communication [4]. MH typically presents as a nodule on the midline of the scalp (especially the occipital area), or less commonly on the upper face or paravertebral region. Most cases present in childhood or shortly after birth, but occasionally the lesion is initially noticed during adolescence or adulthood. The average age of five cases reported by Suster and Rosai [1] was 14.3 years-old (range: 4 months to 46 years). We report a case of MH of the scalp in a 78-year-old man.

The lesion manifested as a well-circumscribed solitary subcutaneous tumor of 5 × 5cm diameter on the right parieto-occipital area of the scalp (figure 1A). It was firm, non-tender, non-movable and covered by normal hair-bearing skin. The patient said that it had been present as a small nodule since his childhood, but that its size had recently increased. There was no history of trauma to the area, and his other medical and familial history was not specific. A computed tomography (CT) scan of the head revealed a soft-tissue mass with inconsistent density. No bony defects or intracranial tumor was found. Lipoma was suspected, and surgical excision was performed.

Histopathologically, under low-power magnification, the lesion was composed of mature adipose tissue with stroma of dense collagenous fibers. Intermixed with the collagenous fibers were clusters of cuboidal, epithelioid cells (figure 1B). Under high-power magnification, these cuboidal, epithelioid cells had scant eosinophilic cytoplasm, and oval, vesicular nuclei. They had indistinct cell borders and formed nests between the collagen bundles showing a pseudo-infiltrative pattern (figure 1C). No mitoses or nuclear atypia was present. Immunohistochemically, these cells were positive for epithelial membrane antigen (EMA) (figure 1D) and vimentin (figure 1E), but negative for AE1/AE3, CD34, CD31, S-100 and alfa-smooth muscle actin, in keeping with the features of meningothelial cells.

In our case, the featured network of pseudovascular spaces lined by meningothelial cells described by Suster and Rosai [1] was absent. Nevertheless, due to the hamartomatous nature of our case, which showed an admixture of adipose, collagenous fibers and ectopic EMA-positive meningothelial cells, we diagnosed this lesion as MH. Our case probably represented a variant of type 1 primary cutaneous meningioma (PCM) [2], a tumorous proliferation of meningothelial cells.

The histopathological differential diagnosis of our case should include metastatic carcinoma and spindle cell/pleomorphic lipoma. Metastatic carcinoma can be distinguished by the presence of cytological atypia, mitosis and keratin positivity. Spindle cell/pleomorphic lipoma is characterized by a mixture of fat tissue, CD34-positive spindle cells or multinucleated giant cells, and ropey collagen bundles, which is different from our case and thus can be ruled out.

13 cases (8 males/5 females) of MH have been reported (similar cases have probably been reported in other terms before the first description by Suster and Rosai [1] in 1990); of these, 11 were subcutaneous tumors or nodules on the scalp (7 were in the occipital area, 2 were in the parieto-occipital area, 2 were in the vertex), 1 was a nodule on the forehead and 1 presented as swelling in the sacral region.

Although in the majority of the cases of MH no underlying bony defect or communication to the CNS is detected, reports of bone defects on CT imaging or a fibrous tract connected to dura mater, fluid leaking during surgery, have been reported occasionally. Imaging studies to exclude any communication to the CNS should be done before any invasive procedure is performed.

The presence of ectopic meningothelial elements may pose a diagnostic problem to dermatologists. In our case, awareness of meningothelial cells was the key to the microscopic diagnosis. The characteristics of meningothelial cells are as follows: they are EMA-positive cuboidal cells with scant eosinophilic cytoplasm and oval, vesicular nuclei. They tend to form nests wrapping around collagen bundles.

Our case is the oldest patient ever reported. Dermatologists should be aware of MH in the differential diagnosis of a lump on the scalp, even in older patients. MH is indolent in growth, although the rapid onset of growth (as in our case) has also been reported [4]. However, the reason for the sudden growth of the tumor in the present case is unknown.

Disclosure

Financial support: none. Conflict of interest: none.

References

1 S Suster, J. Rosai Hamartoma of the scalp with ectopic meningothelial elements. A distinctive benign soft tissue lesion that may simulate angiosarcoma Am J Surg Pathol 1990; 14: 1-11.

2 DA Lopez, DN Silvers, E.B. Helwig Cutaneous meningiomas-a clinicopathologic study Cancer 1974; 34: 728-744.

3 DA Sibley, P.H. Cooper Rudimentary meningocele: a variant of primary cutaneous meningioma J Cutan Pathol 1989; 16: 72-80.

4 L Di Tommaso, C Fortunato, V. Eusebi Meningothelial hamartoma located in the forehead Virchows Arch 2003; 442: 509-510.