Alveolar Rhabdomyosarcoma of the Parotid Region: A Cytopathological Diagnosis.

Dear Editor,

Rhabdomyosarcoma (RMS) is the commonest sarcoma of the childhood and adolescence age group with head and neck region and extremities being the most frequent locations.[1] However, RMS of the salivary glands are rare and represent 3.5% of all the neoplasms in a series of salivary gland lesions in children.[2] Fine needle aspiration cytology (FNAC) is a relatively non-invasive, cost-effective procedure with high accuracy which may aid in the diagnosis of such rare neoplasms of the salivary gland.[2] As most of the RMS is not exclusively localized to the parotid gland at the time of presentation, the primary site is referred to as the “parotid region.”[3]

We report a case of parotid region rhabdomyosarcoma diagnosed on FNAC and aided by immunohistochemistry (IHC) on cell block in a 7-year-old female, who presented with a complaint of firm swelling measuring (5 × 4) cm in the right parotid gland along with breathing difficulty [Figure 1a]. The patient was initially treated conservatively on antibiotics considering the predominance of benign inflammatory lesions in this age group; however, the swelling did not subside and continued to increase in size. A computed tomography (CT) scan of the neck revealed a large enhancing mass extending from the right parotid into the ipsilateral parapharyngeal space and masticator space. Fine-needle aspiration cytology (FNAC) of the parotid was performed using a 23-gauge needle and the smears were stained with Papanicolaou (Pap) and May Grunwald-Giemsa (MGG) stains. Material for cell block was obtained with an additional pass.

Figure 1

(a) Right parotid swelling (b) Tumor cells were arranged in sheets and had an occasional rosette-like pattern (MGG, 400x) (c) Tumor cells had eccentrically placed nuclei with irregular contours (Pap, 200x) (d) Cell block showing rosette-like arrangement (H & E, 200x) (e) Tumor cells showing cytoplasmic positivity for Desmin (IHC, 200x) (f) Tumor cells showing nuclear positivity for Myogenin (IHC, 400x)

The smears showed good cellularity comprising of small to medium-sized cells with a moderate amount of cytoplasm. These cells were arranged in sheets and had an occasional rosette-like pattern. The nuclei were eccentrically placed with irregular nuclear contours and inconspicuous nucleoli [Figure 1b and c]. No hemorrhage or necrosis was noted in the cytology smears. The rosette-like pattern was more prominent in the cell block [Figure 1d]. A panel of immunohistochemistry (IHC) was done on the cell block to rule out differential diagnosis of alveolar rhabdomyosarcoma, extraosseous Ewing's sarcoma, myoepithelial carcinoma, lymphoma, and granulocytic sarcoma. The tumor cells were immunopositive for Vimentin, Desmin, Myogenin, and MyoD1 [Figure 1e and f]. The tumor cells were negative for CD45, TdT, Smooth muscle actin (SMA), p63, CD117, CD34, CD99, and FLI1.

Based on the cytomorphology and IHC findings, a diagnosis of alveolar rhabdomyosarcoma of the parotid region was made. The patient had bilateral cervical lymphadenopathy, which showed metastasis by the tumor cells on FNAC. Bone marrow study showed involvement of bone marrow by the tumor cells. A CT chest showed evidence of lung metastasis. The Intergroup Rhabdomyosarcoma Study Group (IRSG) of the patient was staged at IRSG IV.

The patient was planned for chemotherapy and radiotherapy however the patient expired after 25 days of diagnosis.

Alveolar RMS arising from the parotid region is extremely rare with only a few cases reports being reported in the literature.[34] Unlike embryonal rhabdomyosarcoma, the alveolar type rarely affects the head and neck area. Alveolar RMS most commonly affects the extremities and trunk.[4]

RMS may show a variety of cytological morphology ranging from spindled, plasmacytoid to small round blue cells.[2] Alveolar RMS show predominantly small round cells which may render it impossible to differentiate it from other round blue cell tumors on cytology alone.[2] IHC is of utmost importance in ruling various cytological look-alike neoplasms. The various differential diagnoses considered in the present case were extraosseous Ewing's sarcoma, lymphoblastic lymphoma, granulocytic sarcoma, and myoepithelial carcinoma. Negative immunoreactivity for CD99 and FLI1 ruled out extraosseous Ewing's sarcoma, CD45 and TdT negativity ruled out lymphoblastic lymphoma, CD117 and CD34 negativity ruled out granulocytic sarcoma, and negative expression of SMA and p63 ruled out myoepithelial carcinoma. Positive immunoreactivity for Vimentin, Desmin, Myogenin, and MyoD1 helped in confirming the diagnosis of alveolar rhabdomyosarcoma.

The prognosis for alveolar rhabdomyosarcoma is poor with early metastasis to lymph nodes, lungs, pleura, pancreas, and bone. Bone marrow examination should be done as part of the staging process.[4] The present case also had metastasis to lymph nodes, lung, and bone marrow at the time of presentation and she expired after 25 days of diagnosis.

FNAC provides a reliable, safe, minimally invasive approach for the diagnosis of such rare neoplasms in the parotid region. IHC on cell block is of great help in arriving at a diagnosis in such a rare neoplasm. We reported the full work-up of the case to highlight the importance of FNAC and subsequent IHC done on cell block which could pinpoint to a diagnosis of RMS of the parotid and hence avoiding biopsy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.