Image-guided fine-needle aspiration of retroperitoneal masses: The role of the cytopathologist.

BACKGROUND: Retroperitoneal tumors constitute a difficult diagnostic category as they are not easily accessible. The advent of image-guided fine-needle aspiration (FNA) has resolved this problem significantly. AIMS: We present a short study based on guided aspiration of retroperitoneal tumors, in which we have tried to assess the role of image-guided fine-needle aspiration cytology as a tool for pre-operative diagnosis.
MATERIALS AND METHODS: The study was conducted on patients diagnosed with retroperitoneal masses. FNA was performed under image guidance with the help of ultrasonography and/or computed tomography; smears were prepared and meticulously screened according to a fixed protocol. The results were analyzed to determine sensitivity, specificity, and diagnostic efficacy of cytopathological diagnosis using image-guided FNA techniques.
RESULTS: We assessed 38 patients with retroperitoneal masses. In all cases, adequate cellular material was obtained. No major complications were encountered. Statistical analysis was carried out in 35 cases; sensitivity, specificity, and diagnostic accuracy were 100% in these cases.
CONCLUSION: FNA under image guidance should be considered a first-line diagnostic approach for retroperitoneal and other abdominal tumors, although caution should be exercised in case selection. In areas where advanced tests are not available, the cytotechnologist and cytopathologist have a very important role to play in ensuring accurate diagnoses.

Introduction

The application of image guidance to aspiration cytology has brought about a revolution in the field of cytopathological diagnosis. Where initially only superficial and easily palpable lesions could be subjected to aspiration, now, even deep-seated lesions can be visualized and aspiration can be performed with a high degree of accuracy and minimum discomfort to the patient. The need for exploratory surgery and its attendant morbidity is thus reduced significantly. Image-guided fine-needle aspiration (FNA) of retroperitoneal and pelvic masses is now an increasingly common diagnostic procedure.

Any structure visualized by dynamic ultrasonography (USG) can be reached quickly and precisely by a fine needle in any desired plane with constant visualization of needle tip during insertion.[1] As compared to its more illustrious counterpart, the computed tomography (CT) scan, USG has additional advantages in that it is comparatively inexpensive, can be easily repeated, and avoids the risk of radiation exposure.[2]

CT is far superior in terms of visualization of the lesion. Masses in critical areas are best suited for CT-guided fine-needle aspiration cytology (FNAC).[3] Also, the problems encountered in cases of obese patients, presence of bowel gas, patient positioning, and dressing can all be overcome.[4]

With such applications, it is not unusual to occasionally diagnose unexpected lesions in which the combined radiological and cytological assessments enable the clinician to pursue a line of further investigation and make a correct management decision.[5]

The following study covers cases of retroperitoneal masses which were initially diagnosed with the aid of aspiration under image guidance. The cytopathological features of the aspirates and diagnostic efficacy of the procedure have been analyzed.

Materials and Methods

The study was conducted in the Department of Pathology in collaboration with the Department of Radiodiagnosis at our hospital. This was a 1-year study and included patients presenting with symptoms related to abdominal masses and confirmed by USG and/or CT.

After a detailed clinical workup and with the patients' consent, radiological examination was conducted in the Department of Radiodiagnosis. Nearly, all the cases required a CT; in some cases, a USG was done initially, while in others, the clinician requested a direct CT examination. Aspiration was carried out by a trained pathology resident, with the help of a trained cytopathology laboratory assistant/technician. The mass to be aspirated was localized by USG or CT scanning. The site of puncture was marked on the skin and the area was cleaned with an antiseptic solution. A 22-23 gauge needle attached to a 10-mL syringe was used for aspiration. In some deep-seated masses, a lumbar puncture needle was found to be more suitable. The needle was inserted under guidance into the lesion. When it was clearly visualized within the mass, suction was applied and several passes were made within the lesion. The needle was withdrawn after release of suction and the site of puncture was sealed. The slides were grossly examined on the spot, where the slides were heavily blood-stained or appeared to have scant material, the aspirate was repeated.

The material obtained was smeared on glass slides and immediately fixed in 95% alcohol and submitted to the cytopathology laboratory for routine processing. In cases where aspirated material consisted of fluid, it was processed by centrifugation in the cytospin at 700-800rpm for 10 min. The smear thus obtained was stained by hematoxylin and eosin (H and E) and Papanicolaou stains. Diagnosis was made by light microscopic examination of the stained slides. However, it was not possible to carry out ancillary tests, such as immunochemistry and/or flow cytometry, as the use of these tests is unfortunately limited in low-resource settings. Correlation with histopathological findings was carried out in those cases where the patients underwent surgery.

Results

Out of 38 cases of retroperitoneal masses, 14 patients were diagnosed with renal lesions, 9 cases were of adrenal masses, and 8 cases were of pancreatic malignancies. The remaining 7 cases comprised miscellaneous tumors. Adequate material was obtained in all cases [Figure 1].

Figure 1

Computed tomography (CT scan (a) Large heterogenous density mass (renal cell carcinoma) in left kidney; (b) Contrast-enhanced CT with a solid-cystic lesion in right adrenal gland (adrenal cyst); (c) Post-contrast CT showing an enhancing mass arising from right adrenal gland (adrenal carcinoma); (d) Contrast-enhanced CT scan: Heterogenous low-density mass in head and uncinate process of pancreas (Pancreatic adenocarcinoma)

Renal masses

This group comprised nine male and five female patients, with an age spectrum of 4-68 years. Of the 14 cases of kidney lesions, only 3 (21.4%) were benign renal cysts. The remaining 11 cases (78.6%) were malignant, comprising eight cases of renal cell carcinoma and three of Wilms' tumor.

Aspirates from benign renal cysts revealed degenerating epithelial cells and numerous macrophages scattered in a clear background [Figure 2a]. In cases of renal cell carcinoma, smears were rich in cells, which were arranged singly or in cohesive sheets and dominated by hemorrhage and necrosis. The cells were large, with abundant pale to pink, finely vacuolated or granular cytoplasm and large, atypical nuclei [Figure 2b].

Figure 2

(a) Renal cyst: Cytospin preparation of aspirated fluid showing numerous macrophages in a clear background (H and E,×250); (b) Renal cell carcinoma: Large cells with abundant vacuolated cytoplasm and atypical nuclei against a hemorrhagic background (H and E, ×500); (c) Adrenal cyst: Hemorrhagic aspirate with foamy macrophages (H and E, ×250); (d) Adrenal adenocarcinoma: Papillary clusters of malignant cells with eosinophilic, vacuolated cytoplasm and overlapping, hyperchromatic nuclei with coarse chromatin (H and E, ×500)

Only two patients with renal cell carcinoma underwent surgical intervention. The histopathological diagnosis in these, based on features of conventional renal cell carcinoma, corroborated the cytological diagnosis. The other patients were treated with radiotherapy.

Aspirates from three cases of Wilms' tumor (pediatric age group) showed numerous undifferentiated small cells arranged singly or in tight clusters. Some rosette-like structures were also noticed. The cells had scant blue cytoplasm, with small, round or ovoid hyperchromatic nuclei and multiple small nucleoli. Mesenchymal differentiation in the form of spindle cells was also appreciated [Figure 3a]. Histopathology sections demonstrated the presence of the three major components of the tumor, undifferentiated blastema, mesenchymal, and epithelial tissue forming abortive glomeruli and tubules.

Figure 3

(a) Wilm's tumor: Spindle-shaped mesenchymal cells along with small, round, hyperchromatic blastemal cells (Pap, ×250); (b) Adenocarcinoma pancreas: Tumor cells with hyperchromatic nuclei arranged in acinar pattern (H and E, ×125); (c) Lipoma: Adipocytes with clear cytoplasm and compressed nuclei (H and E, ×250); (d) Liposarcoma: Lipoblasts with vacuolated cytoplasm and scalloped, hyperchromatic nuclei (↑) (H and E, ×250)

Adrenal tumors

In contrast to the predominance of male patients with renal tumors, we encountered seven females and two males in this category. Out of the nine cases studied, 4 (44.4%) were of benign adrenal cysts; 2 (22.2%) were diagnosed as neuroblastoma, and three cases (33.4%) as adenocarcinoma.

The aspirates from adrenal cysts showed paucity of cellular material, composed of erythrocytes, foamy macrophages, and sparse inflammatory cells in a proteinaceous background [Figure 2c].

In contrast, rich cellularity was on display in smears of neuroblastoma and carcinoma of the adrenal gland. In aspirates from adenocarcinomas, smears were obtained with some blood and hemosiderin-laden macrophages scattered randomly in the background. The tumor cells were arranged in cohesive clusters with tendency to form microacini [Figure 2d]. Cells were large with moderate to abundant pink cytoplasm, with focal vacuolation. Nuclear overlap, hyperchromasia, anisokaryosis, and coarse granular chromatin helped to clinch the diagnosis.

Numerous, individually scattered small cells along with groups showing prominent nuclear molding and rosette formations were seen in smears of neuroblastoma. The cells had high nuclear-cytoplasmic ratio with oval or irregular hyperchromatic nuclei, prominent nucleoli, and negligible amount of cytoplasm [Figure 4a]. Fine fibrillary material, the neuropil, could be seen in the center of the rosettes as well as scattered freely in the background.

Figure 4

(a) Neuroblastoma: Richly cellular smear composed of small, round, blue cells, with nuclear molding, rosette formations, and fibrillary neuropil (H and E, ×250); (b) Chordoma: Large physaliphorous cells with abundant, vacuolated cytoplasm and small nuclei in a myxoid background (↑) (H and E, ×250)

The benign cysts were seen to regress after aspiration and surgery was not required. Among the malignancies, the patients diagnosed with adenocarcinoma were referred to specialist centers, while cases of neuroblastoma were treated non-surgically; hence, histopathological correlation was not possible in these cases.

Pancreatic masses

A total of eight cases were seen with mean age of presentation being 55 years. Five patients were females. All were diagnosed as adenocarcinomas.

Good cellularity smears were obtained with large malignant cells arranged in sheets and microglandular pattern [Figure 3b]. Loss of cell cohesion, nuclear crowding, and hyperchromasia were other prominent features. Detached single cells were also observed frequently in a hemorrhagic and necrotic background. The cases were not amenable to surgery; therefore, cyto-histopathological correlation was not possible.

Miscellaneous lesions

A total of seven cases were grouped under this category. Of these, 4 (57.2%) were diagnosed as lipomas, two cases (28.6%) as liposarcoma, and one as a teratoma.

Aspirates from the lipomas yielded clusters or sheets of mature adipocytes [Figure 3c]. The diagnoses were confirmed on histopathology.

Image-guided aspirations from liposarcomas also yielded fatty material, which on microscopic examination revealed the presence of spindle and round cells against a hemorrhagic background [Figure 3d]. A second population of cells (lipoblasts) was evident in the smears, with cytoplasmic vacuolization and atypical scalloped nuclei. Occasional binucleate and multinucleate cells were also present. The detection of typical lipoblasts was critical in differentiation from benign lipomas. Histopathological examination and confirmation of cytological diagnosis were possible in all cases.

A single case of retroperitoneal teratoma yielded a thick and greasy aspirate. Nucleate and anucleate cells could be seen along with inflammatory cells in an amorphous background. Histopathology showed features of a benign cystic teratoma, with mature squamous epithelial lining, a large amount of keratin, hair follicles, and mature cartilage.

We also observed a single case of sacrococcygeal tumor, which was diagnosed as chordoma on FNAC. The findings could not be correlated histologically as the biopsy material was inadequate. The smears revealed a background of myxoid ground substance and large physaliphorous cells with abundant, pale, vacuolated cytoplasm, well-defined cell borders, bland nuclei, and small nucleoli [Figure 4b].

Overall, we obtained a sensitivity and diagnostic accuracy of 100%; there were no true negatives or false positives. Histopathology was available for only 12 patients. The breakup of cases and cyto-histopathological correlation is shown in Table 1. In the remaining cases, benign cysts were not subjected to intervention; among the malignancies, some patients were referred to higher centers, while others were treated with radio/chemotherapy. Further follow-up was, however, not possible.

Table 1

Correlation of cytological and histopathological diagnoses

Discussion

USG and CT are valuable technological advances in the field of radiodiagnosis. Previously inaccessible lesions can now be safely sampled and many more areas of the body are now routinely aspirated under guidance. This has led to a reduction in open biopsy and two-stage surgical procedures by providing a probable diagnosis prior to surgical treatment. Close co-operation between the radiologist and cytopathologist now ensures maximum efficiency of man and machine, minimizes patient discomfort, and enables rapid diagnosis in a cost-efficient manner.

Although the major use of image-guided FNA has been in the evaluation of retroperitoneal soft tissue masses and renal lesions, it also finds application in the investigation of adrenal and pancreatic lesions.[6-10]

No major complications were encountered in the present series, the only complaint being mild pain and discomfort at the puncture site during and after aspiration for a few hours. It is therefore a safe procedure in experienced hands. This is validated by the results of other major studies.[11-14] Technically, possible complications include hemorrhage and hematoma formation, infection, pancreatitis, and risk of tumor seeding along the needle-track.[111516]

In all the cases that underwent guided FNA, adequate diagnostic material was obtained and characteristic cytological features were noted. We did not include the three cases of renal cysts while carrying out statistical evaluation as cytology cannot exclude the possibility of malignancy in such lesions.[17] Histopathological diagnosis was possible in a small number of cases only but with 100% cyto-histological agreement. We therefore recorded a sensitivity and diagnostic accuracy of 100% in 35 cases. No true-negative or false-positive cases were seen in our study. Most of the major studies have reported high rates of sensitivity and accuracy.[6711-14] Nevertheless, we do acknowledge the fact that our values can partially be attributed to the limited number of cases that were studied and the small number of samples that were actually available to us for histopathological diagnosis.

Excellent cytomorphology was noted in all the smears prepared, which again shows that in experienced hands, image-guided FNA is a reliable means of diagnosis. The cytological findings were in accordance with published literature.[6-101318-20]

In a hospital which predominantly caters to patients from a low socioeconomic background, it is often difficult to provide advanced ancillary tests. Most patients are unable to afford these tests. In such situations, the role of cytomorphology cannot be overemphasized. With experience and careful examination of well-prepared slides with sufficient cellularity, an accurate diagnosis can be reached in almost all cases, as seen in our study. As such, the cytotechnologist and cytopathologist work in tandem to ensure the success of the entire exercise.

The simple renal cyst can sometimes pose problems for the pathologist. Atypical macrophages or the presence of necrosis or blood can definitely cause a suspicion of malignancy.[21]

Although renal cell carcinomas can be diagnosed fairly accurately on cytology, difficulties can arise in the presence of massive hemorrhage or extensive necrosis.[21] False-positive diagnoses are possible if the cells are aspirated from the adrenal cortex or an adrenal cortical carcinoma.[21]

Wilms' tumor is the most common renal malignancy in children.[22] A monophasic Wilms' tumor with a predominant blastemal component can be very difficult to differentiate cytologically from other round cell tumors. In such a situation, immunocytochemical studies are necessary to make a decision.

The aspiration of adrenal masses must be undertaken after correlation with radiological findings (such as tumor size)[7] and blood chemistry analysis. The dilemma of diagnosis can be explained by the fact that normal adrenal cortical cells can be similar to cells of an adenoma, and adrenal cortical carcinomas can cytologically mimic renal cell carcinomas.[7]

The differential diagnosis of neuroblastoma includes other small round cell tumors. However, the location of the mass and the presence of neuropil[23] are very helpful in making a diagnosis on cytopathology. Immunochemistry can help to clinch the diagnosis in difficult cases.

FNA of the pancreas is mostly concerned with diagnosis and/or confirmation of malignancy. Although complications are uncommon, there are published reports of pancreatitis and more importantly, dislodgement of tumor cells into the peritoneal cavity by the needle.[24]

The retroperitoneum is a site for several neoplasms, including metastatic tumors, sarcomas, and lymphomas. A recent report describes the diagnosis of retroperitoneal liposarcomas using endoscopic ultrasound-guided FNA.[25] Apart from these, the retroperitoneal lymph nodes are important sites for both neoplastic processes and non-neoplastic conditions. In the investigation of retroperitoneal masses, CT scanning with lymphography is especially useful as it allows the localization of small lesions.[12]

The results reaffirm that FNA under image guidance should be considered a first-line diagnostic approach for retroperitoneal and other abdominal tumors and lesions. However, a word of caution is essential. It is necessary to be selective in deciding which masses are to be aspirated. Further, in some cases, cytology cannot be relied upon to exclude malignancy, as in the case of renal cysts[17] and cysts of large size. Histopathology remains the gold standard in such cases. Therefore, the choice between pre-operative cytology and excisional biopsy lies with the surgeon. As in all cases, a thorough clinical workup is a pre-requisite and can help in reaching a good clinical decision.