Contributed by Anja Harder, MD1; Eloise Müller-Schulte 2; Astrid Jeibmann 2 , MD; Johannes van de Nes 3, MD, Ph.D;
Uwe Wildförster, MD 4; Werner Paulus, MD 2
1 Institute of Pathology, HELIOS Klinikum Emil von Behring, Berlin, Germany
2 Institute of Neuropathology, University Hospital Münster, Münster, Germany
3 Institute of Pathology and Neuropathology, University Hospital Essen, Essen, Germany
4 Department of Neurosurgery, Bergmannsheil und Kinderklinik Buer, Gelsenkirchen, Germany
A 68-year-old diabetic male patient was initially admitted due to left-sided hearing loss, balance impairments and left-sided facial palsy in 2001. At that time he had been complaining of left-sided tinnitus for years. An MRI showed a mass in the cerebellopontine angle on the left side, causing mild compression of the brainstem. He underwent neurosurgery in 2002. The operation revealed that the 7th and 8th cranial nerves were profusely infiltrated by the tumor. The mass was excised by retrosigmoidal craniotomy and both nerves were preserved. Postoperatively, facial nerve palsy was still apparent. Gait and eyelid closure improved thereafter, whereas anacusis showed no improvement. He then underwent annual follow-up examinations. In 2006 T1-weighted horizontal MRI with gadolinium contrast enhancement demonstrated tumor recurrence (Fig. 1). Moderate increase in growth was seen in 2007 (Fig. 2), but surgical intervention was not indicated at that time. In 2010 the patient suffered from increasing dizziness and balance impairment. MRI examination revealed tumor growth with medial expansion and brainstem compression (Fig. 3) and second operation was performed. The tumor was again localized within the caudal cerebellopontine angle compressing the caudal brainstem and cranial nerves as well as the left crus cerebelli. On craniotomy the tumor was almost completely extirpated with a small residue remaining attached to the caudal cranial nerves. After operation, slight paresis of the 6th cranial nerve and hoarseness occurred.
The formalin-fixed biopsy samples were processed with standard paraffin technique, and stained routinely (H&E, elastica van Gieson) as well as with antibodies against neurofilament, Ki67, vimentin, desmin, S-100beta, smooth muscle actin, cytokeratins (clone MNF116, CK7), GFAP, CD34 and EMA. Both the initial as well as the recurrent tumor were composed of monomorphic spindle-shaped, often bipolar cells embedded within a myxoid stroma. Intermingled mature striated muscle fibers were seen, single or in small groups (Figs. 4, 5). The fine cytoplasmic tails were relatively short, and special architectures were not seen. Nuclei were round to oval and contained finely dispersed chromatin. Mitotic activity was absent. Blood vessels showed fibrosis. Lymphocytic infiltrates were apparent. Immunohistochemically, all cells and the muscle fibers showed strong positivity for desmin (Fig. 6) including positivity of striated muscle cells (Fig. 6, insert) as well as for vimentin. Weak to moderate S100 immunoreaction was seen in about 40% of tumor cells (Fig. 7) Reactions for cytokeratins (MNF116, CK7), GFAP, EMA, smooth muscle actin, and CD34 were negative in the tumor cells. Neurofilament positive nerve fibers were not seen. The Ki67/MIB-1 proliferation index was lower than 2%. What is the diagnosis?