Dear Editor:
Myopericytoma (MPC) is a rare benign soft tissue tumor originating from perivascular myoid cells1. Although MPC has been confused with several tumors such as hemangiopericytoma in the past, the World Health Organization (WHO) has classified it as a distinct soft tissue tumor2. Globally, <200 cases have been described in the literature, and <30 lesions have been reported on the hands3.
A 49-year-old woman presented with a 1 cm×1 cm asymptomatic bluish nodule on the right knee (Fig. 1A). The patient had noticed the lesion 5 years earlier, with no history of trauma. Histologic findings showed well-circumscribed dermal proliferation of ovoid-to-spindle-shaped cells concentrically surrounding thin-walled blood vessels (Fig. 1B). Cytological atypia and mitosis were absent. Immunohistochemistry revealed that tumor cells were positive for α-smooth muscle actin (SMA) and negative for CD34 and desmin (Supplementary Fig. 1). The patient was diagnosed with MPC, and there was no local recurrence after 6 months.
Fig. 1. (A) A 1 cm×1 cm bluish subcutaneous nodule on the right knee. (B) Proliferation of ovoid-to-spindle-shaped cells (perivascular myoid cells) concentrically surrounding thin walled blood vessels (H&E, ×150). (C) A 0.5 cm×0.7 cm centrally eroded subcutaneous nodule on the pulp of the right second finger. (D) Proliferation of perivascular myoid cells arranged in a concentric pattern showing onion ring appearance. Thin-walled and branched vessels (staghorn vessels) are observed within the tumor nodule (H&E, ×200). We received the patient’s consent form about publishing all photographic materials.
A 50-year-old man presented with a 0.5 cm×0.7 cm centrally eroded nodule on the pulp of the right second finger (Fig. 1C). He noticed the lesion 4 years prior and had previously received cryotherapy. Punch biopsy revealed dermal proliferation with ovoid-to-spindle-shaped cells arranged uniformly in a concentric perivascular pattern with thin-walled branching staghorn vessels (Fig. 1D). Tumor cells were positive for SMA and negative for CD34 and desmin (Supplementary Fig. 2). After diagnosed with MPC, the patient had no recurrence for 2 years.
Previous studies have reported that MPCs have male predilection and usually involve the lower extremities. However, in Korea, MPC shows female predilection4. Tumor cells comprising MPCs are thought to originate from myofibroblasts or pericytes. Myofibroblasts are modified smooth muscle cells that usually stain positive for SMA and negative for desmin. Pericytes are contractile cells that ubiquitously exist around capillaries and venules.
The diagnosis of MPC heavily depends on two aspects: histological ultrastructural patterns and immunohistochemical staining. The striking histopathologic feature of MPC is the concentric perivascular arrangement of plump spindle-to-ovoid shaped perivascular myoid cells. Immunohistochemistry findings include tumor cells stained positive for SMA, indicating myoid differentiation, but negative for desmin and CD34. This immunohistochemical phenotype clearly distinguishes MPC from other tumors such as angioleiomyomas, that are positive for desmin, and solitary fibrous tumors that are frequently positive for CD34 (Table 1).
Table 1. Comparison of histologic features and immunohistochemical profile between myopericytoma and other mimicking tumors.
| Myopericytoma | Myofibroma | Glomus tumor | Angioleiomyoma | Solitary fibrous tumor | |
|---|---|---|---|---|---|
| Histopathologic features | Onion ring appearance*, staghorn vessels† | Onion ring appearance*, zonation/biphasic appearance, staghorn vessels†, hyalinized areas | Glomus cells with oval nuclei, myxoid stroma poor vasculature, scant smooth muscle cells | Smooth muscle bundles, thick-walled vessels | Spindle cells in haphazard arrangement, hyalinized to collagenous stroma, staghorn vessels† |
| Immunohistochemistry | SMA (+) | SMA (+) | SMA (+) | SMA (+) | SMA (–) |
| CD34 (–) | CD34 (–) | CD34 (+/–) | CD34 (+/–) | CD34 (+), usually | |
| Desmin (–) | Desmin (–) | Desmin (–) | Desmin (+) | Desmin (–) |
SMA: α-smooth muscle actin. *Onion ring apperance: concentric perivascular arrangement of plump spindle-to-ovoid myoid cells, †Staghorn vessels: thin-walled and branched vessels.
Several soft tissue tumors, such as myofibroma (MF), glomus tumor, and angioleiomyoma resemble MPC. According to 2020 WHO classification2, MF was reclassified under MPC, which reflects dominant perspectives on MPC with a spectrum of histologic growth pattern encompassing MF. Despite overlapping histologic features with MPC, MF can be distinguished by predominant biphasic zonation between tumor nodules. Glomus tumors are distinguished from MPCs by connective tissue surrounding the tumor nodules. Angioleiomyoma is distinguished by its histologic features, as it mainly shows smooth muscle bundles in a fascicular pattern. Sometimes MPC is confused with pyogenic granuloma in histology (Fig. 1C, D). But the absence of onion ring appearance and immunohistochemical profile distinguishes it from MPC. The prognosis of patients with MPC is usually excellent, as local recurrence after excision is <4%5.
Footnotes
CONFLICTS OF INTEREST: The authors have nothing to disclose.
FUNDING SOURCE: None.
SUPPLEMENTARY MATERIALS
Supplementary data can be found via http://anndermatol.org/src/sm/ad-21-188-s001.pdf.
(A) Scan view of the myopericytoma (MPC) on the right knee, which is located in the reticular dermis to subcutaneous layer (H&E, ×12). (B) Tumors cells exhibiting diffuse positive expression of α-smooth muscle actin (SMA, ×20). (C) Tumor cells are not stained by CD34, while the endothelial lining of the vasculature is stained (CD34, ×20). (D) Negative expression of desmin in tumor cells (desmin, ×20).
(A) Scan view of the the myopericytoma (MPC) on the right second finger, which is located in the superficial to deep dermis. (B) Tumor cells are diffusely stained with of α-smooth muscle actin (SMA, ×70). (C) CD34 expression is exclusively observed in the endothelial lining of the vasculature and not in the tumor cells (CD34, ×70). (D) Negative expression of desmin in tumor cells (desmin, ×70).
References
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Supplementary Materials
(A) Scan view of the myopericytoma (MPC) on the right knee, which is located in the reticular dermis to subcutaneous layer (H&E, ×12). (B) Tumors cells exhibiting diffuse positive expression of α-smooth muscle actin (SMA, ×20). (C) Tumor cells are not stained by CD34, while the endothelial lining of the vasculature is stained (CD34, ×20). (D) Negative expression of desmin in tumor cells (desmin, ×20).
(A) Scan view of the the myopericytoma (MPC) on the right second finger, which is located in the superficial to deep dermis. (B) Tumor cells are diffusely stained with of α-smooth muscle actin (SMA, ×70). (C) CD34 expression is exclusively observed in the endothelial lining of the vasculature and not in the tumor cells (CD34, ×70). (D) Negative expression of desmin in tumor cells (desmin, ×70).