Fine needle aspiration cytology of metastatic alveolar rhabdomyosarcoma.

Rhabdomyosarcoma (RMS) is an aggressive malignant soft tissue tumor that arises from primitive striated muscle cells called rhabdomyoblasts. RMS is a rare tumor in adults, and involvement of the sinonasal area is extremely rare, comprising only 1.5% of all reported head and neck RMSs. Alveolar RMS, mainly seen in adults, has the worst prognosis. Incidence of lymph node metastases is more common in this type compared with the other forms. Fine needle aspiration cytology (FNAC) has been used extensively in the diagnosis of metastatic malignancies. However, metastatic soft tissue sarcomas are often overlooked, primarily due to the low frequency with which they occur. Here, we report a rare case of metastatic alveolar RMS in the cervical lymph nodes of an 18-year-old girl that was detected by FNAC. After 6 months, the patient came with a huge mass involving the nasal vestibule and the upper lip. Histology of both the main mass and the lymph nodes revealed alveolar RMS.

Introduction

Rhabdomyosarcoma (RMS) is an aggressive malignant soft tissue tumor that arises from primitive striated muscle cells (rhabdomyoblasts). It is the most common soft tissue malignancy in children. It can arise from almost anywhere in the body, but is most common in the head and neck region (orbit and eyelids). It is a malignant mesenchymal tumor that frequently involves the urogenital tract and the extremities. The paranasal sinuses are very rarely involved, comprising only 1.5% of the reported head and neck cases.[1] Alveolar RMS tends to occur in slightly older patients with a mean age of 15–20 years. Within the head and neck region, embryonal RMS is the most common RMS, whereas alveolar and pleomorphic tumors are more common in the extremities.[2] Clinically positive neck nodes at diagnosis are unusual in head and neck RMS, but microscopic involvement is found by an elective neck dissection. The incidence of lymphatic metastases from the head and neck region in RMS has been reported to be 7%.[3] The alveolar variant exhibits the greatest propensity for lymph node metastasis; 33% are associated with positive regional nodes on initial examination and 75–85% develop either regional or distant nodal deposits, sometimes during the course of the disease.[4] Cervical metastasis in RMS of the nose and paranasal sinus was present in 38% of the patients. This type of RMS has the worst prognosis.[5]

Klijanienko et al.[6] determined the diagnostic cytomorphological features of RMS on the fine needle aspiration material. The fine needle aspiration morphology was also correlated with histology. Alveolar subtypes were more cellular than the non-alveolar ones. Similarly, alveolar subtype RMSs compared with non-alveolar ones exhibited more rhabdomyoblastic cells, alveolar structures, giant, multinucleated cells, mitotic figures, and cytological atypia. Inversely, spindle-shaped cells were more frequently seen in non-alveolar RMSs. Atahan et al.[7] reviewed the cytological findings of RMS with histological confirmation and proposed a morphological subtyping based on the most prominent cytologic features.

Case Report

An 18-year-old female presented with complaints of left-sided nasal obstruction, occasional epistaxis, and swellings on both sides of the neck of 2 months duration. On examination, the left nasal passage was found to be filled with a small granular and fleshy tumor, with some purulent discharge from the left side of the nasopharynx. There were bilateral enlarged submandibular lymph nodes that were firm and non-tender, measuring 3 cm × 3 cm. Fine needle aspiration cytology (FNAC) was performed on both the cervical lymph nodes.

FNAC smears revealed a high degree of cellularity and displayed tightly cohesive clusters of homogenous tumor cells, with occasional gland-like spaces as well as single isolated cells with abundant karyorrhectic debris. Roundish cell clusters around the connective tissue fragments or vascular cores with central lumen, frequently anastomizing in irregular sheaths, referred to as “alveolar structures,” were well appreciated [Figure 1].[6] The smears were composed of small round cells with cytonuclear atypia; few spindle-shaped and plasmacytoid cells with eccentric nuclei were also seen [Figure 2]. Mitotic figures, binucleated, multinucleated cells, and necrotic background were also well appreciated. The tumor cells exhibited round to oval nuclei with mild irregularity and finely granular chromatin with inconspicuous nucleoli and scanty cytoplasm. Most of the criteria used by Klijanienko et al.[6] to diagnose and subtype RMS were present in this case, except frequent presence of rhabdomyoblast. Intracytoplasmic inclusions, rosettes, and fibrillary material were not identified. Based on these FNAC findings, the diagnosis of metastatic deposit of small round cell tumor, probably alveolar RMS, was suggested.

Figure 1

Smear shows alveolar structures composed of roundish cells around a connective septa or vascular structures (H and E, ×400)

Figure 2

Cellular smear made up of small round cells with high nucleocytoplasmic ratio, few plasmacytoid type of cells with a typical multinucleated cell, and few gland-like spaces (H and E, ×400)

The patient was referred to the Department of E.N.T. for further management but, unfortunately, the patient was lost during follow-up. Then, after about 6 months, she returned to the Department of E.N.T. with a frank fungatating growth involving the nasal vestibule and the upper lip area along with persistent cervical lymphadenopathy. Pre-operative baseline parameters and chest radiograph were within normal limits. Under general anesthesia, the tumor was excised along with the submandibular lymph nodes. Grossly, the excised specimen consisted of the tumor mass with part of the upper lip along with bilateral submandibular lymph nodes. The tumor mass measured 2.5 cm × 3 cm, with an irregular elevated surface, and was of firm consistency. The cut-surface showed whitish fragile areas.

The lymph nodes measured 3 cm × 3 cm, with a smooth surface and areas of hemorrhage; the cut surface revealed a homogenous white area. Multiple sections were given from the tumor and the lymph nodes.

We also took an imprint smear from the lymph nodes. It showed cytomorphology closely simulating its corresponding histology. The septa and the gland-like arrangement were easily made out.

Sections from the tumor showed non-cohesive clusters of large anaplastic malignant cells with moderate to abundant eosinophilic cytoplasm and pleomorphic nuclei with coarse chromatin pattern, mitotic activities, and nuclear vacuolations.

Cells with abundant dense eosinophilic tapering cytoplasm, suggestive of rhabdomyoblastic differentiation, were seen. The tumor cells were seen shedding from the fibrous septa (alveolar growth pattern). Multinucleated giant cells with peripherally arranged nuclei were seen frequently.

The histological findings of the lymph nodes showed evidences of infiltration with total effacement of lymph node architecture and focal outstanding sinusoidal infiltration and a prominent alveolar growth pattern, interspersed with occasional typical rhabdomyoblasts.

The reticulin-stained section showed a typical criss-cross arrangement of the fibres, which was also evident in the hematoxylin and eosin (H and E)-stained sections. Part of H and E-stained section had a solid or diffuse architecture in which the reticulin stain was helpful. The phosphotungstic acid hematoxylin stain showed striations in the tumor cells pointing toward the origin of the tumor, i.e. from the muscles.

Immunohistochemistry was carried out, which included leucocyte common antigen (LCA), Vimentin, S-100, and Cytokeratin, of which Vimentin and S-100 were positive.

Based on the above findings, histopathology of the resected specimen was reported as alveolar RMS with a metastatic deposit of the same in the lymph nodes.

Discussion

RMS bears a close resemblance to various stages in the embryogenesis of normal skeletal muscle, but its pattern is much more variable, and ranges from poorly differentiated tumors that are very difficult to diagnose without immunohistochemical or electron microscopic examination to a well-differentiated RMS.

Morphologically, “solid” forms of alveolar RMS can also be seen, which might simulate the round cell areas of the embryonal RMS. However, a uniform cellular pattern, multinucleate giant cells, and incipient alveolar features, supported by cytogenetic studies, help in differentiating between the two. It is important not to confuse the two as the alveolar type carries a less-favorable prognosis.

Differential diagnosis of malignant small round cell tumors that includes Ewings sarcoma, neuroblastoma, malignant lymphoma, and poorly differentiated carcinoma were considered.[8] In Ewings sarcoma, the cells are dissociated or arranged in a cluster of loosely cohesive cells. The nuclei are round or irregular and usually lack nucleoli. Two populations of cells are usually found, large pale cells and smaller dark cells.[9] The cytoplasm is pale blue and contains variable numbers of punched-out vacuoles that correspond to glycogen deposits. Variable numbers of pseudorosettes may be seen and mitotic figures are rarely detected; such features were not present in our case.

In neuroblastoma, small clusters of cells are usually separated by a pale blue to light purple fibrillar matrix.[10] The delicate fibrillary background stroma that represents the neuropil was not seen. Also, no rosette was seen. In neuroblastoma, rosettes are usually seen.

Malignant lymphoma cells are dominated by a single cell pattern and lymphoglandular bodies. Moreover, immunostain for LCA was negative in our case, which ruled out lymphoma, and because cytokeratin was negative, poorly differentiated carcinoma was also ruled out.

Alveolar RMS involves tumors that are mostly undifferentiated in nature and therefore readily develop distant metastasis and thus have the worst prognosis. In this case, lymph node metastasis was already present at the time of diagnosis.

It is difficult to make a definite diagnosis of small round cell tumors based on cytological findings alone. Therefore, it is essential for the cytopathologist to evaluate clinical data and histological and immunohistochemical findings upon encountering these morphological features so that the possibility of this condition is not overlooked.