Page 201 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Chapt er 10
188
Cytological features

VetBooks.ir • Cellularity is variable, often high.
Background: often clear and variably haemodiluted. It may contain small cytoplasmic
•
fragments (lymphoglandular bodies).
• Epitheliotropic lymphoma: most frequently composed of small- to medium-sized lymphoid
cells. Mitoses are rare or absent. Less commonly, neoplastic cells are medium-large, with
high mitotic activity.
• Non-epitheliotropic lymphoma: neoplastic cells are often large with high numbers of
mitoses. NEL composed by a predominance of small lymphocytes has also been observed.
Small cell forms have also been observed.
• Small cell forms:
• Nuclei are small to intermediate (< 1.5 rbc), round, often indented, irregular and cer-
ebriform. They have a finely clumped chromatin and small nucleoli can be seen.
• The cytoplasm is scant to moderate and pale basophilic.
• Mitoses are usually absent, or present in very low numbers.
• Large cell forms:
• Nuclei are large (> 2.5 rbc), round, often convoluted and indented, with coarse granular
chromatin and prominent nucleoli.
• The cytoplasm is moderate in amount and variably basophilic.
• Marked nuclear pleomorphism and binucleation have been reported. Mitoses can be
numerous and atypical.
• Inflammatory cells are frequently present. A neutrophilic and macrophagic inflammation is
often observed secondary to ulceration of the lesions. Secondary opportunistic bacterial
infection can develop. In the non- epitheliotropic lymphoma, an infiltrate of histiocytes, neu-
trophils and mixed lymphocytes can accompany the neoplastic component (inflammatory
NEL), making the diagnosis of a lymphoma more difficult.

Differential diagnoses
• Small cell lymphoma:
• Lymphocytic (chronic) inflammation
• Regressing cutaneous histiocytoma
• Large cell lymphoma:
• Histiocytic neoplasm (e.g. cutaneous histiocytoma, histiocytic sarcoma and reactive
histiocytosis)
• Mixed inflammatory dermatitis
• Subcutaneous panniculitis-like T-cell lymphoma:
• Panniculitis