Primary parasagittal myoepithelioma in a paediatric patient: review of the literature and illustrative case

Abstract

Myoepithelial tumours are a rare form of salivary gland neoplasm, and their occurrence in the central nervous system is exceedingly rare. The authors report the case of an 18-year-old Filipino man presenting with headache and weakness, and on imaging showing an extensive parasagittal tumour at the left posterior parietal area with extracalvarial extension. There was no systemic disease. The patient underwent surgery to excise the tumour, with histopathology showing findings consistent with myoepithelioma. There was no further treatment, given the benign histology of the lesion, but there was recurrence after 8 months. Repeat surgery was done for the patient and he is for adjuvant radiotherapy. This appears to be the 10th reported case of a central nervous myoepithelioma, and the first case in the Philippines of a primary parasagittal myoepithelioma in a paediatric patient. Further information is needed to provide diagnostic and therapeutic recommendations.

Background

Myoepithelial neoplasms were originally described in the salivary glands but have since been described in other locations; however, their occurrence in the central nervous system (CNS) is exceedingly rare, and review of the literature has revealed only nine other cases of myopeithelioma of the CNS (cavernous sinus, sella, orbital apex–middle cranial fossa, interhemispheric fissure, right cerebral hemisphere, parieto-occipital lobe, trigeminal cave, cerebellopontine angle and cranial dura–falcine).

These tumours have varying proportions of myoepithelial and epithelial cells that behave in a spectrum ranging from benign to malignant (myoepithelioma to myoepithelial carcinoma). They are thought to arise from ectopic glandular tissue or embryological remnants of vestigial glandular structures.

Case presentation

We report a case of an 18-year-old Filipino man presenting with a parasagittal mass with extensive extracalvarial extension (figure 1A); systemic examination showed no other palpable masses with special attention to the salivary glands. This patient had previously presented with gradual right-sided weakness at 9 years of age; subsequent cranial MRI with contrast showed a 6.4×5.9×5.4 cm T1 hypointense, T2 hyperintense heterogeneously contrast-enhancing mass at the left frontoparietal lobe with surrounding perilesional oedema; the preoperative working impression was a primitive neuroectodermal tumour. He underwent left parietal craniotomy, gross total excision of a parasagittal tumour with intraoperative frozen section revealing malignant round cell neoplasm. Postoperatively, the weakness improved and no adjuvant treatment was undertaken due to poor follow-up.

Figure 1.

Preoperative photos showing the extensive extracalvarial growth of the tumour and the involvement of the overlying skin of the scalp (A). Postoperative photos at follow-up (B).

He was asymptomatic until 2017, when there was note of a slow-growing, non-tender, firm extracalvarial mass associated with occasional headache.

Investigations

MRI with contrast showed a T1-hypointense, T2-hyperintense heterogeneously contrast-enhancing left posterior parasagittal mass with extension to the parieto-occipital scalp; the parasagittal component measured 6.0×4.4×3.0 cm, and the extracalvarial component measured 17.4×15.1×16.7 cm (figure 2A). There was erosion of the adjacent parieto-occipital bones. Cerebral angiogram (figure 2B–G) showed a hypervascular mass centred in the left posterior parietal area, crossing the midline. Blood supply was from the occipital artery branches of both external carotid arteries (ECAs), parietal branches of the superficial temporal arteries and middle meningeal branches of both internal maxillary arteries. Due to the surgically accessible blood supply, preoperative embolisation was not done.

Figure 2.

Imaging. T1-weighted axial, coronal and sagittal contrast-enhanced images showing the parasagittal and extracalvarial extent of the tumour (A). Cerebral angiogram: supply from the branches of the left ECA (B–D) and supply from the branches of the right ECA (E–G). ECA, external carotid artery.

Differential diagnosis

Due to the previous history of left parietal craniotomy and excision of a round cell neoplasm at 9 years of age, the working impression for this admission was a recurrent primitive neuroectodermal tumour. A primary parasagittal myoepithelioma was not entertained at this point.

Treatment

He was admitted under the neurosurgery service of the Philippine General Hospital (PGH) and referred to plastic surgery for closure. The patient underwent bilateral parieto-occipital craniectomy, excision of the tumour with primary closure (figure 3). General endotracheal anaesthesia was performed by the neuroanaesthesia service, after which the patient was placed in prone position in a horseshoe head rest. A team of three neurosurgeons did the excision of tumour simultaneously.

Figure 3.

Patient in prone position for surgery—bilateral parieto-occipital craniectomy, excision of tumour with primary closure.

The tumour was devascularised by ligating the supply from ECA branches prior to tumour removal. It was firm and fleshy, brownish, very vascular with large tumour vessels; there was calvarial erosion, and it extended into the epidural space without intradural extension. After tumour excision was done by the neurosurgery team, primary closure was achieved by the PGH Plastic Surgery team. Postoperatively, the patient was admitted to the neurosurgical critical care unit and did not develop any deficits. Oral feeding was started the following day after surgery and he was transferred out to the regular ward, and eventually discharged on the fifth postoperative day.

Histopathological examination (figure 4) showed myoepithelial cells arranged in cords and nests; there was uniform architecture with a myxoid stroma, without any atypia. Immunohistochemical analysis of the initial parasagittal tumour and the tumour recurrence showed both tumours to be vimentin-positive and negative for CD99, desmin, glial fibrillary acidic protein (GFAP), leukocyte common antigen (LCA), smooth muscle actin (SMA), muscle speficic actin (MSA), S-100 and synaptophysin. The case was signed out by the neuropathology service as a myopeithelioma after extensive discussion during the hospital’s tumour board. Postoperative CT scan with contrast showed apparent complete excision of the tumour.

Figure 4.

(A) Low-power and (B) high-power views. (C) Immunohistochemistry. Microscopy showed myoepithelial cells arranged in cords and nests; there was uniform architecture with a myxoid stroma, without any atypia. Immunohistochemical analysis of the initial parasagittal tumour and the tumour recurrence showed both tumours to be vimentin-positive and negative for CD99, desmin, GFAP, glial fibrillary acidic protein; LCA, leukocyte common antigen; SMA, smooth muscle actin; MSA, muscle specific actin), S-100 and synaptophysin.

Outcome and follow-up

Initially, no adjuvant treatment has been given to the patient due to the benign histology of the tumour. However, the patient presented with right upper and lower extremity weakness 8 months after excision, and on repeat imaging, there was note of tumour recurrence (10.0×8.0×2.0 cm) for which the patient underwent repeat surgery and excision. Postoperatively, the patient is back to baseline status with resolution of the weakness and good wound healing (figure 1B). He is for adjuvant radiation therapy, given the aggressive course despite the benign histology.

Discussion

Myoepithelial tumours are neoplasms with a spectrum of biological behaviour, having epithelial and myoepithelial elements. They arise from myoepithelial cells in the epithelium of glandular structures (ie, sweat, lacrimal, salivary or mammary glands).¹ Although it is not unusual to encounter them in the salivary glands or the skin, their occurrence in the CNS is exceedingly rare.^{1 2} The differentiating capacity of myoepithelial cells is broad, and they can be in the benign end of the spectrum as myopeithelioma or in the malignant end as myoepithelial carcinoma.³ Benign myoepitheliomas are more common compared with carcinomas which have been known to metastasise to the lungs, bone, soft tissue, skin, liver and brain.^4–6

They are well circumscribed and lobulated, with neoplastic cells appearing epithelioid, spindled, ovoid, polygonal, plasmacytoid, clear cell or hyaline.^{4 5} Because of the variable appearance, the pathological diagnosis is challenging.^{6 7} The immunophenotype is also varied, with combinations of cytokeratin, vimentin, S-100, EMA, SMA and GFAP expression.³

These are rare neoplasms of myoepithelial differentiation,⁸ and literature review revealed only nine other cases in the CNS (cavernous sinus, sella, orbital apex, interhemispheric fissure, cerebral hemisphere, parieto-occipital lobe, trigeminal cave, cerebellopontine angle and falx).1–3 7–13 Including the case presented, the total number reported is 10 (table 1). This review shows that CNS myoepithelioma occurs in equal proportion for adult and paediatric patients, without gender predilection, with malignant behaviour commonly affecting paediatric patients (50%–65% of cases).^{5 6} Most present with a painless, slow-growing, non-tender cutaneous or subcutaneous mass, with larger sizes associated with pain and mass effect,⁵ as was seen in the case. Some myoepitheliomas of the soft tissues harbour ESWR1 (Ewing Sarcoma Breakpoint Region 1) gene translocations,¹¹ but genetic testing was not done for this case.

Table 1.

Summary of all cases of CNS myoepitheliomas, demographic features and outcomes reported in the literature

Location in the CNS		Age/gender	Intervention	Behaviour	Outcome
1. Nieder et al13	Sella13	34/F	STE×2, RT, CTX	Malignant	Unfavourable—died 20 months after
2. Erdogan et al 3	Falx3	47/F	GTE, RT	Malignant	Favourable, stable at 4 months of follow-up
3. Hong et al 8	Cavernous sinus8	48/F	STE×2	Malignant	Unfavourable, died 4 months after diagnosis
4. Vajtai et al10	Cerebellopontine angle 10	32/M	GTE	Benign	Favourable—alive at 72 months of follow-up
5. Hayward et al1	Dura of the orbit1	17/F	GTE	Benign	Favourable
6. Choy and Pyrel9	Falx9	13/M	GTE	Benign	Favourable—no recurrence, 30 months of follow-up
7. Choy and Pytel9	Right cerebral hemisphere 9	10 months/M	STE	Malignant	Unfavourable—died 8 days after surgery
8. Gupta et al12	Parieto-occipital lobe 12	2/F	GTE, RT, CTX	Malignant	Favourable, clinically well at 30 months of follow-up
9. Gowripriya et al11	Meckel’s (trigeminal) cave11	43/M	GTE	Benign	Favourable
10. Present case	Parasagittal area	18/M	GTE×2, RT	Malignant	Favourable, clinically well at 18 months of follow-up

CNS, central nervous system; CTX, chemotherapy; F, female; GTE, gross total excision; M, male; RT, radiation therapy; STE, subtotal excision.

Reports of these tumours occurring in the sellar region is related to the occurrence of salivary gland rests in this area^{3 11}; however, the location of the tumour in the aforementioned case is remote from these rests. Second, dura is derived from neuroectoderm and mesenchyme, both of which are unlikely to give rise to myoepithelial cells.³ Based on the study by Gowripriya et al, myoepitheliomas within the dura are thought to arise from the presence of hypothetical multipotent stem cells. The most plausible explanation for the aforementioned case is that it originated from cell rests in the scalp and subcutaneous area and grew to invade the parasagittal area, involving the intracranial compartment. In this particular location, the most important differential diagnosis is a meningioma, since they also have a wide morphology⁹; immunohistochemical staining will aid greatly in the diagnosis.¹¹

For myoepitheliomas of the soft tissue, cytological atypia and high mitotic index predict an aggressive clinical course,³ which was not evident in the case. In other locations (ie, salivary glands and soft tissue), benign myoepithelial tumours have an 18%–20% recurrence rate, with higher risk of recurrence with incomplete resection, but the capacity for metastasis is rare.^{5 9} Myoepithelial carcinomas are more aggressive, irrespective of histological grade or margin status, with a recurrence rate of 39%–42% and distant metastasis in 32%–52% of cases.⁵ Currently, there is no standard therapy, but there is a possibility that piecemeal excision of these tumours contribute to CNS seeding and further spread.⁴ This must be taken into consideration when determining the appropriate surgical approach, and en bloc resection, if feasible, is intuitively the best approach. Evidence for radiation therapy and chemotherapy is sparse, but these are options that can be used, especially in a patient with malignant disease.^{8 13}

Learning points.

• This shows the successful management of a very extensive parasagittal tumour with extracalvarial extension in a paediatric patient, without the need for preoperative embolisation in a low-income country setting.

• By applying the basic tenets in neurosurgery, even complex cases can be managed accordingly together with appropriate comanagement with other specialties (plastic surgery and neuropathology).

• In such cases, where there can be several differential diagnoses (ie, meningioma and hemangiopericytoma), histopathological and immunohistochemical analyses are invaluable.

• Due to the rarity of the lesion, further reporting of similar cases in the literature is recommended with longer follow-up periods to help us define more appropriate treatment strategies.

• Treatment abandonment is an issue, especially in developing countries, which complicates management.