The various patterns described above are not necessarily specific for any one type of tumor but are useful in beginning to formulate a histological differential diagnosis. When combined with other findings, such as the morphology of the tumor cells and stromal and vascular changes, the particular pattern is very helpful.

Stromal Changes

In addition to the appearance of the principal cells, there are many ancillary changes that occur in tumor tissue. These changes again are not specific and diagnostic by themselves but are helpful in making a diagnosis, especially in determining the degree of anaplasia of the tumors.

Necrosis with or without Palisading Necrosis represents death of tissue. There are two types, liquefactive and coagulative, but most of the latter become liquefactive in time as macrophages digest it. Liquefactive necrosis from the beginning is typical of an abscess with pus, but the later stage of any other necrosis can be progressively soft and eventually liquid. Tumor necrosis and radiation necrosis tend to be coagulative with very little phagocytic activity. Necrosis due to infarction is initially coagulative, although grossly soft, but slowly becomes liquefactive with extensive phagocytosis to digest the dead tissue. Even when tumor necrosis is considered to be due to vascular occlusion within the tumor, the dead tumor tissue does not appear to attract many phago-cytic cells. The presence of tumor necrosis with surrounding palisading is indicative of cellular proliferation without concomitant vascular and/or nutrient support and is, therefore, a sign of a rapidly growing tumor. The presence of necrosis is one of critical importance in the diagnosis of glioblastoma. The clinical correlate of necrosis in ependymomas and oligoden-drogliomas is not as clear as in astrocytomas [9].

Radiation also induces coagulative necrosis, predominantly in the white matter, frequently almost identical to that of untreated glioblas-tomas. In cases of a re-operated tumor with a history of previous radiotherapy, it is practically impossible to distinguish the necrosis as being an inherent part of the tumor or secondary to radiation. Some emphasize the presence of pseudo-palisading around the necrosis as specific to tumor necrosis, but the absence is ambiguous since there may not be sufficient numbers of remaining tumor cells necessary to form palisades or their growth rate may have been slowed by the radiotherapy.

Mineralizations (Calcification, Ferrugination and Ossification) Calcification is found in relatively slow growing tumors, including menin-giomas, oligodendrogliomas, gangliogliomas, craniopharyngiomas and astrocytomas, but it can also follow irradiation. It can be found in the parenchyma and adjacent cerebral tissue and in the blood vessel walls in oligoden-drogliomas. In meningiomas, calcification may be present in the form of psammoma bodies, which may show concentric lamination, and in the form of more amorphous larger calcified masses. In craniopharyngiomas, ter-atomas, chordomas and dermoid cysts, the calcification appears as masses of various sizes. Scattered calcified granules within coagu-lative necrosis are typically seen in radiation necrosis.

Cyst Formation and Mucoid Degeneration A cyst is simply a fluid-filled closed cavity and tends to be found in slow-growing tumors. The fluid may be dark brown (so-called "motor oil"), watery (like CSF), xanthochromic of various degrees or hues, milky or mucinous depending on the amount of hemosiderin and protein present, and with or without cholesterol crystals in craniopharyngiomas. The cyst usually arises from liquefactive necrosis or mucoid degeneration of the tumor tissue. In oligodendrogliomas, pilocytic astrocytomas and chordomas, both mucoid degeneration and cyst formation may be present. A large, more or less solitary, cyst is typically found in hemangioblastomas and pilo-cytic astrocytomas that appear as a mural nodule. Numerous microcysts are common in oligodendrogliomas (Fig. 3.18) and astroblastomas as well as in pilocytic astrocytomas. Cysts in craniopharyngiomas or chordomas are variable in size. Cysts are uncommon in menin-giomas and schwannomas and rare in PNETs and germinomas. Glioblastoma has been defined as a multiform glioma, so it should not be surprising to find foci of low-grade glioma with cysts and calcifications, not to forget cysts due to necrosis.

Cure Your Yeast Infection For Good

Cure Your Yeast Infection For Good

The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.

Get My Free Ebook

Post a comment