Ricardo H. Bardales

Tumors of the Sellar Region

In spite of its reduced dimensions, the sellar region is a complex crossroad where many tissues and cells from many different origins converge. This is the main reason why this region can host such a numerous and heterogeneous group of tumors and pseudotumoral lesions (Table 16.1 ).

CNS Germ Cell Tumors

CNS germ cell tumors are similar to their more common extra-neuraxial counterparts, sharing genomic alterations and immunostaining properties.

Intraoperative consultation on pediatric central nervous system tumors by squash cytology

Squash cytology (SC) is a very useful procedure during neurosurgical intraoperative consultation (IOC), and it is especially recommended for the evaluation of soft tumors or tumors that are highly cellular (just the characteristics of pediatric central nervous system [CNS] tumors). The aim of this review is to familiarize pathologists with the range of cytomorphologic appearances that can occur during IOC for pediatric CNS tumors and with the diagnostic dilemmas and pitfalls encountered in this setting. This article is based on the medical literature and the authors experience with a large series of cases accrued over a 12‐year period at 3 institutions. SC is a specially recommended procedure in IOC for pediatric CNS tumors; it reveals the fine cellular details and background features in a manner not seen in corresponding frozen sections. Indeed, a differential diagnosis between histologically look‐alike processes can be achieved with more confidence if SC is employed. Cancer (Cancer Cytopathol) 2015;123:331–46.

Neuronal and Glioneural Tumors

Most neuronal and glioneural tumors are well-circumscribed, slow-growing neoplasias with an early age of presentation. They represent the group of tumors that is most easily overgraded during an intraoperative consultation.

Benign Cystic Lesions

Benign cystic lesions can be classified, according to their cell lining into epithelial-lining cysts (squamous or columnar) and non-epithelial-lining cysts (arachnoid and simple glial). The differential diagnosis depends on their location, as well as on the macroscopic aspect of the cyst content and the microscopic features of the cell lining.

Algorithmic Approach to CNS Intraoperative Cytopathology

The use of algorithms facilitates sample triaging, smear evaluation, and general category interpretation. During intraoperative cytopathology consultation is necessary to keep in mind two facts. First, an absolute diagnostic precision is not necessary; instead, we should provide the neurosurgeon with sufficient information to enable him to make an appropriate decision. Second, it is paramount to avoid an overdiagnosis of malignancy.

Non-neoplastic Disorders

The cytologic method is a very useful procedure during intraoperative consultation of non-neoplastic disorders, because the features of inflammatory cells and macrophages, obscured in frozen sections, are nicely preserved in smears. The presence of large number of inflammatory cells or abundant macrophages virtually rules out the diagnosis of neoplasia and leads the diagnosis in the direction of reactive/inflammatory processes, organizing infarct, or demyelinating disease.

Tumors of the Cranial and Spinal Nerves

Schwannomas are common tumors in the posterior fossa and spinal canal, where they produce compressive symptoms and signs. Nerve sheath cell tumors are difficult to crush yielding smears with cohesive tissue fragments without single cells.

Tumors of the Hematopoietic System

Primary CNS lymphoma is actually one of the most frequent intracranial tumors, being non-Hodgkin diffuse large B-cell lymphoma the most prevalent type. They are not surgical diseases and even partial resection is associated with a dismal prognosis. Smears are recommended for intraoperative procedure. High-grade lymphomas show highly cellular smears with a single cell pattern of large atypical lymphoid cells. Low-grade lymphomas can easily be interpreted as being inflammatory or reactive in nature.

Tumors of the Pineal Region

Most pineal-region neoplasms are germ cell tumors, followed by PPTs and gliomas. Given its axial deep-seated localization, stereotactic biopsy is the method of choice for obtaining diagnostic tissue. Cytologic features of PPT are quite different. Pineoblastoma shows an undifferentiated appearance similar to that of embryonal tumors, whereas pineocytoma resembles central neurocytoma with round, uniform pineocytic cells.