patternless pattern

patternless pattern

A term coined by Arthur Purdy Stout for the appearance by low-power microscopy of fibrous mesothelioma, which has a vague storiform pattern. The term has also been applied to hemangiopericytoma and solitary fibrous tumours.
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Grossly, the tumor usually presents a sharply circumscribed mass with smooth, bosselated, or lobulated external surface.[7] Microscopically, classical morphological appearance including 'patternless pattern' caused by variable spindled cells arrayed in the stroma.
The most common patterns are storiform, epithelioid, fibrosarcomatous, or patternless pattern. Less frequently, it consists of malignant phyllodes tumor-like hypercellular stroma and leaf-like glands.
Histopathological diagnosis is challenging and mostly based on a "patternless pattern" on microscopic examination.
(7) Pathologically, these tumors often are made up of narrow cords of cells interspersed with thick bundles of collagen (the "patternless pattern") and admixed with (1) an area exhibiting a prominent hemangiopericytoma-like and angiofibroma-like appearance and (2) a neural-type fascicular area with wavy nuclei and an occasional herring-bone formation.
One classic feature is the presence of spindle cells that grow in a haphazard fashion in a variably cellular stroma, known as the "patternless pattern".
At higher power, DMMs characteristically show a short storiform pattern ("patternless pattern"; Figure 11, B), but this is not specific and can be seen in OP, nor is it present in every case of DMM.
(91,92,95,96) Mangano et al (92) reported the following diagnostic criteria for desmoplastic malignant mesothelioma: a paucicellular fibrotic lesion with a storiform pattern or the "patternless pattern" of Stout and 1 or more of the following 4 characteristics, namely, (1) frankly sarcomatoid areas; (2) foci of bland necrosis; (3) invasion of chest wall or lung parenchyma; and (4) distant metastases.
These appearances were consistent with a so-called "patternless pattern." In some areas, there was vague nuclear palisading.
In contrast to ESTP, solitary fibrous tumor is composed of bland ovoid-shaped to spindle-shaped cells without the cytologic features of perineurioma, arranged in the so-called patternless pattern, and has blood vessels often showing a hemangiopericytoma-like branching.
Although they were first described in the pleura, they have since been described arising in other serosal surfaces and many other sites.[14] Morphologically, SFTs are well-circumscribed but not encapsulated tumors composed of bland spindle-shaped cells with several architectural appearances, including a storiform pattern, fascicles of spindle cells with a wavy, neural appearance, a patternless pattern, abundant myxoid matrix in areas, densely cellular fascicles of spindle cells with a herringbone pattern, and SFTs with atypical multinucleated giant cells admixed with the spindle cell proliferation.[14] Mitoses and areas of necrosis are not identified except in the densely cellular variants, where there may be some nuclear atypia and scattered mitotic figures.
An interlacing fascicular growth pattern or a patternless pattern of the tumor cells in a dense collagenous stroma are not the characteristics of these liposarcomas.
Histologic features characteristic for solitary fibrous tumor are spindle cells arranged in a "patternless pattern" and interlacing collagen bundles.