Pineal gland lesions are rare, with only a few cytologic descriptions occurring in the literature, according to the authors' knowledge. The current article describes the cytopathologic characteristics of 20 such lesions with discussion of differential diagnoses.
Cytologic material was obtained either by fine-needle aspiration biopsy (FNAB) under stearotactic radiologic guidance or by touch imprinting (TI) at the time of frozen sectioning. The 20 specimens include pineoblastoma (five specimens), pineocytoma (four specimens), astrocytoma (three specimens), germ cell tumor (three specimens), meningioma (one specimen), epidermoid cyst (three specimens), and pineal cyst (one specimen). Smears were stained with Diff-Quik and with Papanicolaou and hematoxylin and eosin stains. In selected specimens, immunoperoxidase (IPOX) stains were performed on cell block sections using synaptophysin, neuron-specific enolase, placental alkaline phosphatase, glial fibrillary acidic protein, leukocyte common antigen, cytokeratins, and human chorionic gonadotropin antibodies.
Several cytomorphologic characteristics unique to each lesional category with occasional overlapping features were observed. The unique features included the following: small, hyperchromatic, round to oval cells with frequent rosetting (pineocytoma), with a few specimens in addition showing hypercellularity, crowding, mitoses, and necrosis (pineoblastoma); pleomorphic round cells in a fibrillary background (astrocytoma); large polygonal cells with prominent nucleoli and clear cytoplasm (germ cell tumor); spindled fibroblastic cells (meningioma); anucleate squames and mature squamous cells (epidermoid cyst); and small uniform polygonal cells (pineal cyst). When necessary, IPOX studies supported the morphologic diagnoses.
The pineal gland is a small body (weighing approximately 0.1 g) that is attached to the posterior wall of the third ventricle and enclosed by the pia mater. The gland functions mainly as an endocrine organ and produces the hormone melatonin. Levels of melatonin influence the function of brain centers such as appetite and sleep. Microscopically, the pineal gland has cords and clusters of epithelial-like cells called pinealocytes, surrounded by a rich capillary network.
Pineal lesions are rare, most often occurring in children and young adults.1 The clinical presentation of patients with pineal gland lesions includes headache, paralysis of upward gaze, emesis, and seizures caused by the increased pressure from the expansile mass. Pineal lesions include nonneoplastic cysts and benign or malignant tumors.2–6 The most common neoplasms are germ cell tumors, neoplasms of the pineal parenchymal cells, and gliomas.3, 7 The germ cell tumors include germinomas and teratomas, which arise from embryonic remnants of germ cells. Tumors of pinealocytes are the most common lesions of the gland and include pineocytoma (PC; or pinealoma) and pineoblastoma (PB). A pinealoma is comprised of neoplastic nests of larger somewhat epithelial cells. A PB is a small cell embryonal tumor (a primitive neuroectodermal tumor [PNET]).6 An accurate diagnosis has important clinical and therapeutic considerations.8–12
To our knowledge, there are only a handful of reports of pineal gland lesions reported to date in the cytopathology literature.13, 14 In the current study, we analyzed the cytopathologic characteristics of 20 such cases with elaboration on differential diagnosis.
MATERIALS AND METHODS
Cytologic material was obtained either by fine-needle aspiration biopsy (FNAB) under stereotactic computed tomography guidance or by touch imprinting (TI) at the time of frozen sectioning. For the FNABs, a dedicated neuroradiology suite was used by a team comprising a neuroradiologist, a neurosurgeon, and a cytopathologist. For the immediate on-site evaluation, air-dried, Diff-Quik®–stained smears were used (Baxter USA, Bloomington, IN). Wet-fixed (in 95% ethanol) smears also were prepared and subsequently stained with Papanicolaou stain. Needle rinses with balanced salt solution were used to make paraffin cell blocks. Four-micron sections were stained with hematoxylin and eosin. In selected cases, additional 4-μm sections were used for immunoperoxidase (IPOX) studies using conventional methodology. The antibodies used included synaptophysin, neuron-specific enolase (NSE), placental alkaline phosphatase (PLAP), glial fibrillary acidic protein (GFAP), leukocyte common antigen (LCA), cytokeratins (AE1/AE3), and human chorionic gonadotropin (HCG; Table 1).
Table 2 shows the clinicodemographic data for the patients in the current study. There were 20 specimens from 17 patients. The mean age of the patients was 23 years (range, 1–60 years). There were nine males and eight females (male-to-female ratio, 1.2:1). The most common presenting complaints included headache, nausea, emesis, ataxia, and decreased visual acuity. Radiographic studies most commonly disclosed a predominantly solid (occasionally cystic), hypodense or hyperdense mass in the region of the pineal gland, often associated with microcalcifications and either with or without surface ring enhancement. Diagnostic entities included PB (five specimens), PC (four specimens), astrocytoma (three specimens), germ cell tumor (three specimens), meningioma (one specimen), epidermoid cyst (EC; three specimens), and pineal cyst (one specimen).
Small round blue primitive-appearing cells, occasional pseudorosettes, nuclear molding, mitoses/karyorrhexis, and necrosis. Neuronal differentiation by IPOX studies.
Predominantly intermediate-size monomorphic cells, bare nuclei, perivascular arrangement papillary-like, well formed oval rosettes. Lack mitoses/karyorrhexis. Neuronal differentiation by IPOX markers.
Biphasic cell population comprising mature lymphocytes (often with crushed artifact) and large pleomorphic, polygonal cells with round nuclei, prominent nucleoli, and clear or finely vacuolated cytoplasm. IPOX studies are positive for PLAP, and negative for cytokeratin and GFAP.
Hyperchromatic, pleomorphic small to intermediate-size cells in a fibrillary background. Occasional fine branching capillaries and gemistocytes. IPOX studies are diffusely positive for GFAP. Pilocytic subtype shows elongated nuclei, abundant well formed cytoplasmic processes, and eosinophilic granular bodies. May show Rosenthal fibers.
Whorls and syncytia of bland fibroblastic-type cells with fusiform nuclei. Nuclear grooves and intracytoplasmic inclusions.
Scantly cellular with reactive glial cells and few benign polygonal parenchymal cells.
Abundant mature squamous cells in the absence of any other cellular component. Granular debris. Cell blocks may show intact cyst wall.
All PB specimens displayed an aggressive clinicoradiologic presentation. For example, after an autopsy was performed on one patient, the mesial surface of the patient's brain showed a large, extensively necrotic, hemorrhagic tumor mass involving the ventricles and extending well into the cerebellum (Fig. 1). Smears from the PB specimen were hypercellular and depicted small, round “primitive-appearing” blue cells. Although a significant proportion of the smears comprised single discohesive malignant cells, the tumor showed a tendency to form intact tissue fragments (Fig. 2). The cells in these fragments were tightly crowded and overlapping. Rosette formations were evident focally. The individual cells had round nuclei and a barely discernible rim of pale cytoplasm. The nuclei appeared extremely hyperchromatic with single or multiple small nucleoli. Mitoses/karyorrhexis were numerous. The adjacent cells in these fragments often showed nuclear molding (Fig. 2, inset). Areas of necrosis were readily identifiable. An interesting feature observed in the cell block sections was the tight aggregation of the small round blue cells around the endothelial lining of small vessels reminiscent of peritheliomatous formations. IPOX stains performed in two selected specimens revealed positivity for NSE and synaptophysin and negativity for LCA.
Cellular smears from PC specimens showed numerous single cells and small tissue fragments. The eye-catching low magnification appearance was a perivascular placement of the neoplastic cells, resulting in tight branching “papillary-like” structures (Fig. 3). This type of architecture was evident in 3 of the 4 (75%) PC specimens. The neoplastic cells had intermediate-sized, monomorphic, round nuclei with hypodense chromatin and no nucleoli. Abundant naked tumor cell nuclei were observed in the smear background, resembling lymphocytes. Well formed rosettes were readily identifiable (Fig. 4). In contrast to the PB specimens, no mitotic figures were noted and tumor necrosis was not evident. In none of the specimens were IPOX stains needed for the diagnosis.
Germ cell tumor
All three germ cell tumor specimens in our series were germinomas. The smears showed irregular fragments of large pleomorphic cells. Numerous crushed cells were observed in the smears, which corresponded to the lymphocytic component of the neoplasm. The neoplastic cells had polygonal shapes and relatively abundant cytoplasm that was pale blue to clear and finely vacuolated (Fig. 5). Nuclei were round and had prominent nucleoli. Most cells displayed fragile, easily disrupted cytoplasm, resulting in a significant population of large naked nuclei (Fig. 5, inset). No glandular formations were observed. The slide background was distinctly granular, consistent with the glycogen-rich material commonly observed in gonadal germinomas as well. Cell block sections displayed the biphasic appearance of large pleomorphic malignant cells and background lymphocytes (Fig. 6). IPOX studies showed cytoplasmic staining for PLAP (Fig. 6, inset), and were negative for HCG, GFAP, and cytokeratin AE1/AE3.
Anaplastic astrocytoma specimens displayed diffusely cellular smears comprising small to intermediate-sized neoplastic cells having round, oval, or irregular-shaped nuclei, speckled chromatin with small nucleoli, and scant to no cytoplasm. The smears had a characteristic fibrillary background. One specimen had numerous gemistocytes. Although the tumor cells showed significant pleomorphism, mitoses/karyorrhexis or necrosis was not identified. Both specimens showed fine branching capillary vessels. However, endothelial/microvascular proliferation was not observed. Pilocytic astrocytoma specimens disclosed more elongated, often pointed nuclei, well formed cytoplasmic processes, and occasional eosinophilic granular bodies. Rosenthal fibers were not observed.
The sole specimen of meningioma showed elongated fusiform cells and appeared more mesenchymal in its morphology. Numerous cells depicted prominent intracytoplasmic inclusions and occasional nuclear grooves.
EC specimens displayed abundant anucleate squames and mature “superficial-type” squamous epithelial cells in a granular cystic background. Rare lymphocytes were present. However, no other cell types were observed. Cell block sections revealed portions of the partially intact cell wall comprised of focally keratinizing squamous epithelium.
The single specimen of a pineal cyst showed an uncharacteristic appearance of hypocellular smears with a scant amount of reactive fibrillar glial-type tissue material. Rare aggregates of small, uniform polygonal cells suggestive of pineal parenchyma were also observed.
FNABs and TIs often are performed to evaluate space-occupying lesions of the brain with proven high accuracy. In one recent study, a pathologic diagnosis was established based on cytologic interpretation in 75% of biopsy specimens of central nervous system (CNS) mass lesions without morbidity or mortality.15 Our own experience at Johns Hopkins with an as-yet unpublished study involving 318 consecutive brain FNAB specimens in a 10-year period showed a diagnostic sensitivity of 77% and a specificity of 97%. Other studies also have shown this technique to be diagnostically effective in dealing with a variety of nonneoplastic and neoplastic processes of the CNS.16–19 TI is widely practiced as a useful alternative or adjunct to freezing the tissue material for an intraoperative diagnosis. In our experience, a properly prepared TI provides excellent cytomorphology for an accurate and rapid pathologic diagnosis and is devoid of the freezing artifact so commonly observed when processing minute brain tissue biopsy specimens. In addition, we did not find a major difference when interpreting FNAB and TI smears, with the exception of more intact tumor architecture in FNAB specimens.
The pineal gland is a small organ located in the posterior wall of the third ventricle. Various pathologic processes can involve the pineal gland including pineal cysts and various types of benign and malignant tumors.20 Microscopically, the pineal gland is comprised of clusters and cords of large, epithelial-like cells called pinealocytes, surrounded by a rich capillary network. Tissue smears show that pinealocytes have a delicate cytoplasm and clefted nuclei with folded membranes and speckled “salt-and-pepper” chromatin. Although pineal cysts are tumor-like lesions and not true neoplasms, they are occasionally difficult to distinguish from PC and astrocytoma. From a therapeutic aspect, a precise differential diagnosis is critical. In some cases, the radiographic appearance of a pineal lesion may be consistent with a pineal cyst but the final pathologic diagnosis may be different. Fleege et al.2 reported a series of 19 patients with clinically symptomatic pineal cysts with clinical features including headache, diplopia, nausea and emesis, papilledema, and seizures. The lesions ranged from 0.8 to 3.0 cm. The radiographic appearance of the benign pineal cysts was highly variable, making them difficult to distinguish from other pineal-region tumors.2
The most common tumors involving the pineal region include pineal parenchymal tumors (PPT) and germ cell tumors.3, 4, 10, 13, 20 In a clinicopathologic study by Kang et al.,20 43 pineal-region tumors were described including germinomas, PCs, and PBs.20 PPTs are divided into PCs and PBs. PCs are well differentiated tumors with morphologic features similar to pineal parenchymal cells. PBs are highly malignant neoplasms found in children and young adults that disseminate widely, as is common with PNETs. A definitive distinction between PB and other small round cell tumors (e.g., medulloblastoma and cerebral PNETs) is not possible based on cytomorphology alone. Clinicoradiologic information is critical for an accurate interpretation. Herrick and Rubinstein4 described a series of 28 PPTs including PBs (n = 11) and PCs (n = 7). Pure PBs and mixed PPTs with a pineoblastomatous component are the most common pineal tumors, as was observed in a study by Schild et al.8 who described 30 patients (15 male and 15 female patients) with PPT. Their series included PCs (n = 9), PPT with intermediate differentiation (n = 4), mixed PPT with both PC and PB components (n = 2), and PBs (n = 15).
Germ cell tumors such as germinoma, teratoma, embryonal carcinoma, yolk sac tumor, and choriocarcinoma are observed frequently in the pineal region, either as mixed germ cell tumors or as a pure individual component. Knierim and Yamada12 reported an incidence of 20.4%, of a total of 49 solid and vascular pineal tumors. Pineal germinoma may exhibit carcinomatous differentiation. Ng13 described the cytologic features of five intracranial germinomas. The smears showed sheets of large tumor cells with delicate cytoplasm and prominent nucleoli mixed with mature lymphocytes.
Pineal tumors may metastasize to other locations, making the cytologic diagnosis more challenging. Gindhart and Tsukahara21 described a primary germinoma of the pineal region that metastasized to the lungs and compared the findings with those from a testicular seminoma metastatic to the CNS. The tumor cells from both types of lesions were indistinguishable from one another.21
The cytomorphology of pineal lesions is striking and characteristic patterns may be observed. These include small to intermediate-sized, hyperchromatic, round to oval cells with frequent rosetting (PC) with a few specimens showing hypercellularity and necrosis (PB). Other cytologic features include pleomorphic round cells in a fibrillary background (astrocytoma), polygonal cells with prominent nucleoli and clear cytoplasm (germ cell tumor), benign keratinizing squamous cells (epidermoid cyst), and spindled fibroblastic cells (meningioma). These cytologic features correlated well with histology on the cell block sections, as well as the subsequent histologic material. Ancillary studies such as the use of IPOX are often extremely helpful.
Recognition of the type of lesion is critical and guides the appropriate clinical management of the patient.10 The therapeutic approach to pineal lesions is dependent on the radiographic appearance of the tumor, clinical presentation, age of the patient, and the final pathologic diagnosis. The cytomorphologic appearance of the lesion and an accurate diagnosis therefore are critical to ensure the appropriate management of the patient. The management of pineal cysts may be either aspiration or shunt placement.22 Pineal tumors, when correctly diagnosed, can be treated appropriately and successfully.1 For some patients, early surgery to achieve complete tumor removal may be the best choice. Some pineal neoplasms can be treated successfully with surgery alone. In other patients, surgery followed by radiotherapy may be indicated.9, 10, 20, 23 Prognosis is dependent on tumor type, and obtaining a pathologic diagnosis makes it possible to modify therapy according to tumor type and, therefore, improve patient survival.1, 8, 10