Ghost cell.

Ghost cells (GCs) have been a curious topic since a great deal of time. Extensive research has been done to deduce the true characteristics and formation of these cells. GCs are balloon-shaped, elliptical, pale eosinophilic epithelial cells with pyknotic nuclei, leaving only a faint outline. In routine H and E staining, these cells give shadowy appearance and hence are also called shadow cells or translucent cells. The present article is an attempt to describe in detail about the origin, microscopic appearance, staining property, immunohistochemistry profile and diagnostic importance of GCs. Copyright:

HISTORY

The ghost cells (GCs) were first reported by Highman and Ogden (1936) in cutaneous calcifying epithelioma of Malherbe (pilomatricomas). They are described as swollen, pale, eosinophilic epithelial cells with pyknotic nuclei and faint cellular outline. In H- and E- stained [Figure 1] sections, these cells give a shadowy appearance, hence the name “GC.”[1] They are also called shadow cells or translucent cells. GCs in odontogenic lesions were demonstrated in 1962 by Gorlin et al. in calcifying odontogenic cyst (COC).[2] The GCs are of diagnostic importance and seen in numerous odontogenic and nonodontogenic lesions [Table 1].

Figure 1

H&E-stained ghost cells are swollen, pale, with pyknotic nuclei and faint cellular outline (×10). Inset magnified (×40) H and E view of ghost cells

Table 1

Ghost cell-associated lesions

Odontogenic lesions	Nonodontogenic lesions
Inner enamel epithelium of developing teeth	Cutaneous calcifying epithelioma of Malherbe/pilomatrixoma (in skin)
Eruption cyst	Craniopharyngioma (in pituitary gland)
Glandular odontogenic cyst
Calcifying epithelial odontogenic cyst
Ameloblastoma (granular cell type)
Ameloblastic fibroma
Ameloblastic fibro-odontoma
Odontoameloblastoma/dentinoameloblastoma
Odontoma (complex and compound)
Dentinogenic ghost cell tumor
Ghost cell odontogenic carcinoma

GHOST CELL HISTOGENESIS AND ITS FATE

GCs are always epithelial in origin and are believed to originate from any layer of epithelium i.e., basal, intermediate, or superficial and lack intercellular junctions.[3] Form of true keratinization, prekeratin, stages in the process of ortho, para and aberrant keratin formation, abnormal/aberrant keratinization, highly keratinized epithelial cells and cells which have lost their developmental and inductive effect are the various confusing terminologies used to describe the illusional nature of GCs. Following are the different theories put forward regarding the histogenesis of GC.[4]

Degenerative changes: local anoxia as a cause for degeneration

Coagulative necrosis: altered or absence of cytokeratin expression by GCs was probably due to this coagulative necrosis

Metaplastic transformation of odontogenic epithelium: ischemia as a reason for squamous metaplasia of odontogenic epithelium

Aberrant keratinization and/or accumulation of hard keratin

Abortive formation of enamel matrix: Several investigators have found positive results for enamel matrix proteins in GCs of odontogenic lesions

Terminal differentiation and apoptosis appear to supplement the pathologic progression of the odontogenic/nonodontogenic epithelium to ghost/shadow cells

Role of Wnt-β-catenin-Lef pathway and Notch signaling partially explains the link between tumorigenesis of these lesions and ghost/shadow cell formation and/or calcification

Mucin-induced GC transformation.

ULTRA-STRUCTURAL FINDINGS

Fejerskov and Krogh[5] explained the ultrastructure of GCs in COCs, where they found coarse, thick tonofilament bundles in their cytoplasm, thus distinguishing it from the keratin pattern of the epidermis or oral epithelium which exhibits evenly distributed, fine tonofilaments in the cytoplasm. Endoplasmic reticulum, mitochondria, Golgi apparatus and ribosomes could not be identified in GC. These findings were supported by Regezi et al.,[6] who suggested that GCs represent an unusual or aberrant form of keratin and not the true keratin. In light microscopy, GC contains granular cytoplasm and pale nuclear zone. The electron microscopy shows bundles of tonofilaments of 60–400 nm in diameter, arranged in various directions in the cytoplasm of the GCs. Under TEM, the cytoplasmic fibrils in GCs have been recognized as tonofilaments, sometimes wrongly considered as keratin.[7] Lucchese et al.[8] analyzed the GCs using confocal laser scanning microscope. Based on the different fluorescent effects, they divided GCs into three types: (1) Scarcely detectable, (2) well-resolved and (3) cells with excellent resolution.

STAINING CHARACTERISTICS

To differentiate GCs from similarly stained cornified areas (e.g., poorly decalcified osteodentine, dentinoid, amyloid-like material) various stains were employed like Taenzer-Unna orcein, peracetic acid, azure A-eosin B, periodic acid Schiff with or without diastase digestion, Bensley's modification of Mallory's stain and the DDD stain for sulfhydryl and disulfide of Barnett and Seligman. To differentiate GCs from true dentinoid phloxin-tartrazine stain can be used, it stains both but to a different degree.

GCs showed nonfluorescent to frankly positive yellow fluorescence when observed with the rhodamine B method, dull orange-brown to red with the Mallory's aniline blue reaction and light brown to bright yellow with van Gieson stain [Figure 2]. GCs exhibit various degrees of chromophilia with Heidenhain's iron hematoxylin, negative staining with Alcian blue but some were Periodic Acid-Schiff positive. Masson's trichrome stained GC dull brown, orange-brown or red[4] [Figures 3, 4 and Table 2].

Figure 2

Light brown ghost cells in van Gieson stain (×10). Inset magnified (×40) view of ghost cells

Figure 3

Dark red stained ghost cells in Masson's Trichrome stain (×10). Inset magnified (×40) view of ghost cells

Figure 4

Corresponding hand draw illustration of ghost cells

Table 2

Various stains for ghost cells

Stains used	Reaction of ghost cell
H&E	Pale pink
Goldner stain	Pale red
Masson’s trichrome	Dull brown, orange-brown, or red
Mallory’s	Orange-brown to red
Van Gieson	Light brown to bright yellow
Rhodamine B	Yellow fluorescence
PAS	Magenta

PAS: Periodic acid-Schiff

IMMUNOHISTOCHEMICAL CHARACTERISTICS

GC s show positive immunoexpression for cytokeratins AE1/AE3 and 34 βE12. Takata et al.[9] examined the immunoreactivity of GCs in COCs and dermal calcifying epitheliomas, with antibodies against amelogenin, enamelin, sheath protein (sheathlin) and enamelysin in the cytoplasm of GCs. They found a distinct immunolocalization of the enamel-related proteins within GCs of COC, while similar areas in the calcifying epitheliomas of the skin showed a negative reaction. These findings strengthen the belief that GCs seen associated with odontogenic lesions are different from those seen in the lesions of skin origin.[10]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.