INTRODUCTION
Myopericytoma was described in 1998 in the set of perivascular neoplasms;1 this entity can mimic both neoplastic and vascular pathologies. It is usually characterized by a benign course and a surgical excision can be considered curative. Intracranial localization is unusual and, to date, only nine cases are reported in literature.2-5 Radiation therapy (RT) has been considered in two cases of myopericytoma of the thoracic spine, in order to reduce the risk of recurrence.6,7
We report the first case of combined treatment of a posterior cranial fossa (PCF) myopericytoma with microsurgery and Gamma Knife radiosurgery (GKRS).
CASE REPORT
A 19 year-old female was admitted to the emergency department presenting a short story of rapidly worsening nuchal headache. Medical history was characterized by Hashimoto’s thyroiditis, obesity, unilateral renal agenesis and tonsillectomy. Patient was neurologically asymptomatic.
Brain computed tomography (CT) and subsequent magnetic resonance imaging (MRI) were performed and a right infratentorial expansive solid lesion was found (Figure 1A). The lesion, in proximity to the tentorial edge, was slightly hyperdense on CT. The MRI confirmed a well-demarcated extra-axial lesion, hypointense on T1-weighted and hyperintense on T2-weighted images, with short T1 hyperintense and T2 hypointense stripes. The tumor showed homogeneous enhancement with dural tail sign. Perfusion MRI showed high cerebral blood volume and blood flow values with an increased mean transit time at the level of the lesion, that could be related both to hypervascularization and to intrinsic neoangiogenesis. On spectroscopy MRI, a normal choline/N-acetyl-aspartate ratio was found.
Figure 1.
A) CT and MRI on admission: CT scan showing a right infratentorial slightly hyperdense lesion (A1), DWI sequence showing no diffusion restriction (A2), T2-weighted images showing hyperintense lesion with hypointense spots and stripes (A3), T1-weighted images showing hypointense lesion with hyperintense spots (A4), post-contrast T1-weighted images showing strong and homogeneous enhancement (A5), perfusion MRI showing increased perfusion parameters (A6). B) Post-operative 3-month control MRI showing tumor recurrence: T2-weighted images (B1), post-contrast T1-weighted images, axial view (B2), post-contrast T1-weighted images, coronal view (B3). C) Postradiosurgery 2-year control MRI showing complete disappearance of the tumor: T2-weighted images (C1), T1-weighted images (C2), post-contrast T1-weighted images (C3). D) Histopathologic analysis: hematoxylin and eosin stain showing vasoformative neoplasia composed by vessels surrounded by ovoid, spindle-shaped cells (D1-2), high magnification of tumor myoid cells positive for smooth muscle actin (D3), high magnification of endothelial cells expressing CD34, while perivascular myoid cells are negative (D4), anti-endomysial antibody negative (D5), progesterone receptor negative (D6), glial fibrillary acidic protein negative (D7), inhibin-alpha negative (D8). E) Gamma-Knife treatment planning showing the 15.0 Gy prescription dose line.
In order to avoid intraoperative air embolism, the patient underwent echocardiography which revealed a right-left shunt (patent foramen ovale), so we chose park-bench position.
A reverse hockey stick skin incision and a common suboccipital retrosigmoid approach were performed. The tumor presented as a stretchy lesion, easily compressible, with a macroscopic aspect of vascular giant aneurysm. The lesion was easily dissected from the surrounding cerebellar cortex and a cautious coagulation of the wall lead to a good mass shrinkage. A gross total resection was achieved, dural attachment was coagulated and resected.
Histological examination revealed oval and spindle-shaped cells with a concentric perivascular pattern, showing strong expression of smooth muscle actin and negative for CD34 and glial fibrillary acid protein. The unusual morphology of the lesion and the high pericytic component suggested a second opinion and the final diagnosis was myopericytoma. Postoperative course was uneventful and the patient was discharged home after 7 days.
A scheduled 3-month control MRI showed a tumor regrowth with a supratentorial bulge (Figure 1B). Because of proximity of the lesion to the major sinuses and supratentorial veins, after the evaluation of surgical risks and aiming at a radical excision, we proposed GKRS as salvage treatment.
GKRS was performed with Leksell GK Perfexion (Elekta Instruments) and three-dimensional treatment planning was developed using Leksell Gamma Plan version 8.3 (Elekta Instruments). Neuroradiological localization was routinely performed using stereotactic MRI with specific sequences (1mm-isovoxel volumetric, fat-saturated T1, and steady-state gadolinium-enhanced images). The overall tumor volume resulted 2.75cc and the dose planning parameters were as follows: gross target volume 3.38cc, prescription dose 15.0 Gy, prescription isodose 50.0%, maximum dose 30.0 Gy, average dose 21.4 Gy, integral dose 58.7 mJ, shot number 15. Patient was discharged home the same day of treatment.
On subsequent MRI, the residual lesion progressively reduced in size and completely disappeared within 2 years from GKRS (Figure 1C). The patient remained neurologically asymptomatic.
DISCUSSION
This unusual neoplasm was proposed as an independent subset of myofibroma-like tumor with myocyte as the main proliferating cell.8 Later the first series of myopericytoma was described, composed of seven lesions located in the soft tissue of the extremitites,1 but myopericytoma has been recently described also in the thoracic spine, pineal region, orbit and sellar region.2,4,6,7 Multifocal myopericytomas were found in patients with HIV/AIDS.3,4 Very few cases of intracranial myopericytoma have been reported so far,9 and three located in the PCF.3,5
Myopericytoma is believed to origin from perivascular cells, and has a typical concentric pattern of growth, occasionally with angioinvasive behavior. Due to an incomplete knowledge of the genetic background, molecular drivers for the development of myopericytoma are still unclear.9
Despite the fact that it is usually considered a low-grade tumor, here we describe the first recurrence of an intracranial myopericytoma after a gross-total surgical resection.
Myopericytomas are hyperintense on T2-weighted, hypointense on T1-weighted images, with an intense homogenous contrast enhancement,5 signs of focal intratumoral bleedings or calcification can be found. Osteolysis on surrounding bone structures was observed, as a consequence of the slow growing rate of this tumor.2,6 In our case, radiological features were in line with those of previous reports.5,9 We could not find any paper reporting perfusion or spectroscopy MRI studies on myopericytoma, that showed increased values of perfusion parameters, justified by hypervascularization of the lesion, and a normal choline/N-acetyl-aspartate ratio.
Myopericytomas are composed of oval or spindle-cells with a myoid appearance, eosinophilic cytoplasm and small monotonous nuclei, with a concentric perivascular growth pattern.2,6 Microscopically the lesion showed a small and medium vessels’ proliferation, while mitoses and necrosis were absent. According to the morphology and location of the lesion, the differential diagnoses were among vascular lesion, pericytic lesion, meningioma, fibrous solitary tumor and hemangiopericytoma. Immunohistochemical analysis is reported in Figure 1D.
RT was previously reported for two myopericytomas of the thoracic spine with a total of 45.0 Gy being administered.6,7
According to current literature, myopericytoma is an uncommon neoplasm and intracranial location is extremely infrequent.2,9 A final diagnosis is crucial since myopericytomas can mimic other pathologies, and no preoperative study can provide it. Gross total excision is considered curative but RT has been used to decrease the risk of recurrence.6,7 Tumor disappearance without neurological complications suggests that GKRS might be considered as an effective and safe adjuvant or salvage treatment, for high-risk residual or recurrent intracranial myopericytomas (Figure 1E), in order to avoid a second look surgery. Nevertheless, more reports are needed to understand the origin and growth of this rare tumor, and ultimately to plan the optimal treatment.
ACKNOWLEDGMENTS
The patient gave written informed consent for this report.
Authors’ disclosure of potential conflicts of interest
The authors have nothing to disclose.
Footnotes
Author contributions
Conception and design: Riccardo Lavezzo, Salima Magrini, Antonio Nicolato.
Data collection: Riccardo Lavezzo, Salima Magrini.
Manuscript writing: Riccardo Lavezzo, Salima Magrini, Marta Rossetto, Irene Coati, Matilde Cazzagon, Michele Longhi, Antonio Nicolato.
Final approval of manuscript: Riccardo Lavezzo, Salima Magrini, Marta Rossetto, Irene Coati, Angelo P. dei Tos, Matilde Cazzagon, Nicola Cavasin, Paolo M. Polloniato, Renzo Mazzarotto, Michele Longhi, Francesco Sala, Antonio Nicolato.
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