Diagnosis of a granular cell tumour at the abdominal wall using fine needle aspiration cytology and histology: Case report

Abstract

This case report describes the use of fine needle aspiration cytology to diagnose a granular cell tumour (GCT) that presented as a painless, palpable mass at the abdominal wall in a 50-year-old woman who had had the mass for ≥1 year prior to presentation. Routine haematoxylin and eosin staining of the cytological smears demonstrated that the specimen was predominantly cellular; it contained both cell clusters and single cells with abundant granular cytoplasm and indistinct cell borders. Cells were fragile and had fairly uniform naked nuclei that were scattered with vacuolated and prominent nucleoli. Background material on the smears included eosinophilic, granular cytoplasmic material and some adipose tissue. Neither mitoses nor necrosis were observed. A cytological diagnosis of a GCT was confirmed by histological examination of a surgical specimen stained with haematoxylin and eosin. This case report found that the GCT had a characteristic cytological appearance and that cells with prominent nucleoli can be present in benign GCTs.

Introduction

Granular cell tumour (GCT) is a rare tumour that typically originates from the head and neck region, especially the tongue.^1–3 The majority of GCTs are benign, but they are often misdiagnosed, based on clinical and cytological tests and examination of frozen sections.^4–6 There have been few reports on the cytopathological examination of GCTs.^7–11 The present case report describes the cytological features of a GCT of the abdominal wall, which was diagnosed by fine needle aspiration cytology and confirmed by histology.

Case report

A 50-year-old woman presented to the Department of Surgery, Jinhua Central Hospital, Jinhua, Zhejiang Province, China, in October 2013 with a painless, palpable mass at the abdominal wall that had been present for ≥1 year. On physical examination, a firm, flat, well-defined subcutaneous mass measuring 0.5 × 1.0 × 1.5 cm was detected at the umbilical left lower abdominal wall. The initial clinical diagnosis was suspected lymphnoditis or lipomyoma. Fine needle aspiration cytology of the lesion was performed by a cytologist (L.W.) immediately, using a 10-ml disposable syringe with a 21 G needle to aid in diagnosis. Cells from the mass were aspirated into the syringe and smeared onto a slide. The smear was immediately submerged in 95% alcohol for 10–30 min, followed by routine haematoxylin and eosin (H&E) staining.

Cytological examination revealed the presence of predominantly cellular material composed of both cell clusters and single cells, with abundant amounts of eosinophilic granular cytoplasm and indistinct borders (Figure 1A). There were also fairly uniform naked nuclei that were scattered with vacuolated and prominent nucleoli. The nuclei had regular smooth membranes, finely granular and evenly distributed chromatin (Figure 1B). The background consisted of eosinophilic granular cytoplasmic material along with some adipose tissue. Neither mitoses nor necrosis were observed. There were also some ‘pink cells’ that had abundant eosinophilic granular cytoplasm that resembled a comet tail (Figure 1C) and abnormal nuclei. The clusters of cells had indistinct cell borders with nuclei located on top of their cytoplasm, thus resembling a ‘fried egg’.

Figure 1.

(a) Representative photomicrograph of a smear taken using fine needle aspiration of a firm, flat, well-defined subcutaneous mass, detected at the umbilical left lower abdominal wall of a 50-year-old woman. The smear shows cellular material consisting of both cell clusters and single cells with a fairly uniform scattering of naked nuclei (haematoxylin and eosin [H&E] staining). Scale bar 50 µm. (b) The nucleoli are vacuolated and prominent, the membranes are regular and smooth, and the chromatin appears as fine granules and is evenly distributed (H&E staining). Scale bar 50 µm. (c) ‘Pink cells’ with abnormal nuclei and abundant eosinophilic granular cytoplasm, shaped as a ‘comet tail’ (arrow) (H&E staining). Scale bar 50 µm. (d) Routine histological examination of the surgical specimen shows polygonal cells with small round nuclei and abundant granular eosinophilic cytoplasm. Tumour cells infiltrating adipose tissue are observed (arrows) (H&E staining). Scale bar 50 µm. The colour version of this figure is available at: http://imr.sagepub.com.

Surgery to remove the mass was performed the next day; routine histological examination was carried out 1 week later. During routine histological examination of the surgical specimen, polygonal cells with small round nuclei and abundant granular eosinophilic cytoplasm, as well as areas of vesicular nuclei with prominent nucleoli and local tumour infiltration, were observed. However, neither mitosis nor necrosis were observed (Figure 1D). Immunohistochemistry determined that the tumour cells expressed neuron-specific enolase (NSE), S100, cluster of differentiation 68 (CD68), and vimentin, but not epithelial membrane antigen (EMA) or smooth muscle actin (SMA). Overall, the diagnosis of a GCT at the abdominal wall that was made by cytology was further confirmed by histological examination of the surgical specimen. A panel of immunohistochemical markers were employed to eliminate other possible tumour types, such as: squamous cell carcinoma and basal cell carcinoma (which both expressed EMA but not vimentin); melanoma (which expressed S-100 but not CD68); epithelioid leiomyomas (which expressed SMA but not S100 or NSE); and a nerve-sheath tumour (which expressed S100 and vimentin but not NSE and CD68). The surgical specimen was also stained with periodic acid–Schiff (in addition to H&E) and the cytoplasm was strongly positive. Written informed consent was obtained from the patient to allow publication of this case report. Ethical approval for the study was given by Jinhua Central Hospital.

Discussion

Granular cell tumour is a rare, usually benign neoplasm that can occur in almost any part of the body.^1,2 The features of a malignant GCT (MGCT) include spindle-cell morphology, necrosis, prominent nucleoli, an increased nuclear-to-cytoplasmic ratio, nuclear pleomorphism and an increased rate of mitosis. ³ To be diagnosed as MGCT, at least three of the features listed above must be met.^3,5,12,13 If only one or two of the features are present, then the diagnosis is atypical GCT.^3,5,12–14 Other features of MGCT include a diameter >5 cm and rapid growth.^5,13

Most reports published on the histological features of GCTs have been on lesions from the breast, respiratory tract or digestive tract.^1–3,5,6 Few reports have been on the diagnosis of GCTs by fine needle aspiration cytology.^4,5,7,9–11 One report described a case of GCT in the inguinal region that was misdiagnosed by cytology, ⁴ while another reported that GCT of the breast could be misdiagnosed as breast cancer when using fine needle aspiration cytology. ⁵ El Aouni et al. ⁶ described the cytological features of GCT of the breast and, along with similar studies,^7–11 noted that such features include highly cellular material with abundant eosinophilic granular cytoplasm and indistinct cell borders. In this present case study, the additional cytological features of fairly uniform naked nuclei, scattered with vacuolated and prominent nucleoli, were observed. This present case of GCT could have been misdiagnosed as a malignant tumour if this disease was unknown to the clinicians and/or the smear had not been carefully examined.

In this present case, the GCT cells were fragile and easily broken, which resulted in naked or abnormal nuclei with a comet tail-like trailing of the cytoplasm. The residual cytoplasm was abundant and had eosinophilic granules and indistinct borders. Also, there were clusters of cells with nuclei located on top of their cytoplasm that looked like ‘fried eggs’. The nuclei on the smear were larger than those on the tissue section due to degeneration, and were uniformly naked with scattered vacuolated and prominent nucleoli. This corresponded with areas of vesicular nuclei with prominent nucleoli seen on the tissue section. Features associated with malignancy were not apparent, including a lack of mitosis and necrosis. A report has described the cytological features of atypical GCT of the thyroid as including focal cells with a spindle cell morphology, an increased nuclear-to-cytoplasmic ratio and prominent nucleoli. ¹⁴ In this present case report, the only characteristic associated with malignancy was the presence of focal cells with prominent nucleoli, but they did not reach the atypical standard. Therefore, clinicians should be careful not to misdiagnose these types of cases. GCT has a characteristic cytological appearance of cells with prominent nucleoli, which may be present even in benign GCTs.