Clinical Details: Cerebellopontine angle tumor in a 20-year-old male.
Histopathology:
- Cellular Antoni A area with a fascicular pattern of spindle cells.
- Cellular spindle area with nuclear palisading and Verocay body.
- Cells show indistinct cytoplasmic borders with nuclear degenerative changes.
- Whirling pattern with elongated wavy, buckled nuclei in a fibrillar eosinophilic background.
- Variable size psammomatous calcifications
- NO evidence of melanin pigmentation.
Practical Points of Pathoclinics:
- Calcification and ossification are uncommon in schwannomas. Such foci are typically occurred adjacent to large vessels. Metaplastic bone formation is not common in schwannoma. Cases with psammomatous calcification predominantly occurred in spinal roots and cerebellopontine angle, in a younge age group. Such calcification may cause diagnostic confusion with other mesenchymal tumors, especillay meningioma.
- Meningiomas in the cerebellopontine angle and spinal cord region show thick hyalinized vessels, frequent psammomatous calcification and fibrous spindle cells, which are arranged in a fascicular/whirling architecture. Some of these features in isolation may resemble schwannoma. Very occasionally palisading pattern can be seen in meningioma. Search for characteristic areas like syncytial arrangement of ovoid tumor cells, intranuclear grooves, and frequent whirling pattern favor the meningioma, while nuclear palisading and wavy pointed nuclei favor the schwannoma. Inquiry regarding dural attachment or relation with eighth cranial nerve help to sort out the issue. Here, clinical suspicion was acoustic schwannoma. As psammoma bodies are relatively more frequent in meningioma than schwannoma, the possibility of the former needs to be ruled out. In controversial cases, immunohistochemistry will be done. Meningiomas are positive for SSTR2A (Somatostatin receptor 2a) and EMA while schwannomas are strong and diffuse positivity for S100, while negative for SSTR2A and EMA.
- In cases of prominent psammomatous calcification, another entity which should be rule out is Psammomatous melanotic schwannoma, which has a malignant potential. Spinal location and autonomic nerves are the common site. It has an infiltrative pattern, with sheets and fascicles of uniform spindle schwannian to epithelioid cells, nuclear hyperchromasia and prominent nucleoli. Melanin pigments are variable, scanty to heavy, with coarse clumped granular cytoplasmic pigmentation. Psammoma bodies are seen in up to 50% of cases. Whirling pattern and nuclear palisading can be seen. Such cases are positive for melanoma markers (HMB-45, Melan-A, and tyrosinase) in addition to S100. Many cases of psammomatous melanotic schwannoma is associated with Carney Syndrome (mutations in PRKAR1A). Such cases have an increased tendency for recurrence and metastasis, as well as risk for other tumors related to carney syndrome. So, the distinction is important.
Reference: Din NU, Fritchie K, Tariq MU, Ahmed A, Ahmad Z. Calcification and ossification in conventional schwannoma: A clinicopathologic study of 32 cases. Neuropathology. 2020 Apr;40(2):144-151. doi: 10.1111/neup.12622. Epub 2019 Dec 3. PMID: 31793063.