Ultrasound guided fine needle aspiration cytology in the diagnosis of retroperitoneal masses: A study of 85 cases.

BACKGROUND: The diagnosis of retroperitoneal lesions is one of the most difficult areas in surgical pathology. The retroperitoneal space allows both primary and metastatic tumors to grow silently before the appearance of clinical signs and symptoms. Fine needle aspiration cytology has shown promising role in establishing the diagnosis in this region.
OBJECTIVES: This study was undertaken to evaluate the reliability of ultrasonography (USG)-guided fine needle aspiration cytology (FNAC) in distinguishing between benign and malignant lesions in the retroperitoneum, and to correlate the diagnosis by cytology of retroperitoneal masses with the results obtained by histology.
MATERIALS AND METHODS: The study was carried out on 85 patients presenting over the last five years with retroperitoneal masses on ultrasound.
RESULTS: Out of 85 cases, 32 were of kidney, 27 of lymph nodes, 24 of retroperitoneal soft tissues, and two were of the adrenals. Malignant lesions (47) were more common than nonmalignant lesions (38). In the kidney, the maximum number of cases were of renal cell carcinoma (12-38%), followed by Wilm's tumor (6-19%), pyonephrosis (5-16%), renal cyst (4), angiomyolipoma (2), cortical pseudotumor (2), and tuberculosis (1). Out of 27 cases of retroperitoneal lymphadenopathy, 12 cases (44%) were of metastatic carcinoma followed by non-Hodgkin's lymphoma (8-30%), tuberculosis (6-22%), and Hodgkin's lymphoma (1). The two cases of the adrenals were of angiomyolipoma and metastatic carcinoma. Among the 24 soft tissue tumors in the study, seven (29%) were malignant and 17 (71%) were benign (lipoma being the most common benign neoplasm). Results from histopathological investigations were available in 47 cases, out of which 45 were consistent with the FNAC-based diagnoses. Two cases for which the histopathological results were inconsistent with the FNAC diagnoses, were of renal cell carcinoma, which had been diagnosed as renal cysts on cytology.
CONCLUSIONS: USG-guided FNAC is an inexpensive, rapid, safe, and accurate procedure for the diagnosis of retroperitoneal masses.

Introduction

Retroperitoneum contains the adrenal glands, kidneys and ureters, soft tissues, aorta and its branches, inferior venacava and its tributaries, and numerous lymph nodes, all embedded in a meshwork of loose connective tissue. The retroperitoneal space allows both primary and metastatic tumors to grow silently before the appearance of clinical signs and symptoms.

The diagnosis of retroperitoneal lesions is one of the most difficult areas in surgical pathology. Various imaging modalities such as lymphography, fluoroscopy, and computerized tomography have been utilised in the evaluation of retroperitoneal masses. The advantages of ultrasonography (USG)-guided fine needle aspiration cytology (FNAC) are that it is rapid, inexpensive, versatile, does not require the injection of any contrast medium, and can be easily repeated when necessary.[1] FNAC appears to have a similar diagnostic accuracy in comparing benign and malignant neoplasms as open biopsy.[2] USG-guided FNAC is now widely accepted as a safe diagnostic procedure in various neoplastic and non-neoplastic disorders.[3] This study was undertaken with the following aims and objectives:

To determine the prevalence of different benign and malignant lesions of the retroperitoneum

To study the acceptability and diagnostic accuracy of cytodiagnosis in retroperitoneal lesions

To correlate the diagnosis of retroperitoneal masses by FNAC with the results obtained by histological investigations

Materials and Methods

The present study was carried out on 85 patients presenting over the last five years (from Sep 2003 to Sep 2008) with retroperitoneal masses (kidney, adrenals, soft tissue, lymph node) on ultrasound. After proper workup of patients, including detailed clinical history and examination, FNAC was done under ultrasonographic guidance. Aspiration was done in each case using a 20-22 gauge needle attached to a 20 mL syringe for superficial masses and a 9-cm, 20-22 gauge spinal needle for deep-seated masses. Air-dried smears were stained with Giemsa stain before making cytological diagnoses. Finally, the accuracy of cytological diagnoses was evaluated by comparing them with histopathological diagnoses.

Results

A total of 85 cases of retroperitoneal lesions were studied in patients aged 5-82 years, with most patients aged between 50 and 60 years. Fifty-seven (67%) were males and 28 (33%) females. Out of the 85 cases, 32 were of the kidney, 27 of the lymph nodes, 24 of retroperitoneal soft tissues, and two of the adrenals. The FNAC diagnosis was as follows: Malignant lesions were more common (47 cases, 55.29%) than benign (38 cases, 44.71%). Malignant lesions were common between the ages of 50 to 70 years, whereas benign lesions were common between 30 and 50 years of age. The maximum number of cases belonged to the 50-60 years’ age group (23 cases, 27%).

Among the 38 benign cases in this study, 17 (44.74%) were of soft tissues, 14 (36.84%) of the kidney, six (15.79%) of the lymph nodes, and the remaining one (2.63%) case of the adrenals. In the soft tissue category, lipoma was the most common lesion (seven cases), followed by three cases each of schwannoma and desmoid tumor , one each of spindle cell lipoma, fibromatosis, paraganglioma[Figure 1], and cysticercosis. In the kidneys, there were five cases of pyonephrosis, four of renal cysts, two of angiomyolipoma, two of cortical pseudotumor, and one of tuberculosis. In the lymph nodes, all the six benign cases were of tuberculosis. The one case of adrenal was of angiomyolipoma[Table 1].

Figure 1

Paraganglioma showing small dark uniform nuclei with indistinct cytoplasm (Giemsa, ×100)

Table 1

Distribution of benign retroperitoneal lesions seen by FNAC

Among the 47 malignant cases in this study, 21 (44.68%) were of the lymph nodes, 18 (38.30%) of the kidney, seven (14.89%) of soft tissues, and one (2.13%) of the adrenals. In the lymph nodes, metastatic carcinoma was the most commonly found malignancy (12 cases), followed by eight cases of non-Hodgkin's lymphoma (NHL), and one case of Hodgkin's lymphoma (HL). In the kidney, the most common malignancy was renal cell carcinoma (12 cases), followed by six cases of Wilm's tumor. In the soft tissue category, there were two cases of malignant fibrous histiocytoma (MFH), and one each of leiomyosarcoma, fibrosarcoma, round cell sarcoma, neuroblastoma, and well differentiated liposarcoma respectively. The only case found in the adrenals was of metastatic renal cell carcinoma[Table 2].

Table 2

Distribution of malignant retroperitoneal lesions seen by FNAC

Histopathological correlation was available in 47/85 cases, out of which ten cases were of renal cell carcinoma, six of NHL, six of lipoma, five of Wilm's tumor, three of schwannoma, two each of desmoid tumor, renal cyst, metastatic carcinoma of the lymph node, and one each of fibromatosis, spindle cell lipoma, leiomyosarcoma, fibrosarcoma, MFH, round cell sarcoma, neuroblastoma, liposarcoma, cysticercosis, tuberculous lymphadenitis, and HL respectively. Only two cases were found whose histopathological diagnosis was inconsistent with the cytological diagnosis[Table 3]. Both these cases were of renal cell carcinoma, which had been misdiagnosed as renal cysts on cytology. FNAC had a sensitivity of 94%, specificity of 100%, a predictive value of 100%, and an efficiency of 96% for retroperitoneal lesions; the overall accuracy came out to be 95.92%. Benign retroperitoneal lesions were 100% accurately diagnosed whereas accuracy was 96% for malignant retroperitoneal lesions.

Table 3

Correlation of cytodiagnosis with histological diagnosis

Discussion

There is some reluctance among clinicians and cytologists to use FNAC for the diagnosis of retroperitoneal lesions. The present study has been undertaken to evaluate the acceptability, reliability, and accuracy of cytodiagnosis in comparison to open biopsy. Eighty-five aspirations were performed from patients with retroperitoneal masses (kidneys, adrenals, soft tissues and lymph nodes) in this study.

The age of the patients ranged from five to 82 years, with most of the patients being in the fifth decade of life. Out of 85 cases, 32 were of the kidney, 27 of the lymph nodes, 24 of retroperitoneal soft tissues, and two were of the adrenals. Malignant lesions were more common (47 cases, 55.29%) than benign lesions (38 cases, 44.71%). These results were comparable with those obtained by Miralles et al.[4] but different from those from a study by Nagira et al.[5]

The incidence of different benign soft tissue tumors is broadly reflected in the rate of referral of various tumor types for aspiration. Lipoma was the most common lesion (18.43%) among benign soft tissue tumors, all the cases occurring in the third and fourth decades of life. Similar findings were recorded by Cotran et al.[6] and Rubin et al.[7]

In the malignant soft tissue category, there were two cases of MFH, and one each of leiomyosarcoma, fibrosarcoma, round cell sarcoma, neuroblastoma, and well differentiated liposarcoma respectively. Rekhi et al.[8] also found MFH to be the most frequently encountered sarcoma. Smears of MFH showed marked pleomorphism of cells; some of the tumor cells were small with hyperchromatic nuclei, prominent nucleoli, and scanty cytoplasm[Figure 2]. Others were large with polygonal or spindled shapes. Smears of leiomyosarcoma showed clusters of atypical smooth muscle cells with ill-defined cytoplasmic membranes and cigar-shaped nuclei with blunt ends. Aspirates from fibrosarcomas showed plump, spindle-shaped cells with hyperchromatic nuclei. Neuroblastoma smears were richly cellular, consisting of rosette-like structures with primitive neuroblastic cells and central neuropil. Liposarcoma smears showed polygonal cells with lipid vacuoles[Figure 3]; the nuclei were enlarged and hyperchromatic. Histopathological results were available in 20/24 cases, all of which were consistent with the cytological results. The sensitivity, specificity, predictive value, and accuracy were all thus 100%.

Figure 2

Pleomorphic MFH showing pleomorphic cells with hyperchromatic nucleus and prominent nucleoli (Giemsa, ×200)

Figure 3

Liposarcoma showing polygonal cell with lipid vacuoles. Nucleus is enlarged and hyperchromatic (Giemsa, ×200)

Out of 85 cases, 32 were of the kidney which included renal cell carcinoma (12), Wilm's tumor (6), pyonephrosis (5), renal cysts (4), angiomyolipoma (2), cortical pseudotumor (2), and tuberculosis (1). Twenty-one patients (65.6%) were males and eleven (34.4%) were females. The youngest patient with a renal mass was four years old and had Wilm's tumor; the oldest patient was 80 years old and had renal cell carcinoma. The age of the patients was 4-80 years, a finding which was in accordance with those of Mondal and Ghosh.[9] USG-guided percutaneous FNAC of renal masses was first reported by Kristensen et al.,[10] all the smears from renal masses were richly cellular. Smears from Wilm's tumor showed a blastemal component with epithelial and mesenchymal differentiation; similar findings were recorded by Dey et al.[11] Aspirates from renal cell carcinomas showed malignant cells with finely granular vacuolated cytoplasm, and macronucleoli along with a low N:C (nucleus:cytoplasm) ratio. These were consistent with the findings of Renshaw et al.[12] Angiomyolipoma smears showed smooth muscle cells and fat cells but no epithelial cells, thus excluding a diagnosis of adenocarcinoma; a finding similar to those of Gupta et al.[13] and Handa et al.[14]

Histopathological investigation results were available in 17/32 cases. Two cases found to be renal cysts on FNAC, were actually found to be renal cell carcinomas on histological investigation. This was due to the necrotic cells that had been aspirated on cytology. The sensitivity obtained was thus 94%, along with a specificity of 100%. This finding was similar to those of Pilotti et al.[15] who obtained a sensitivity of 93% and a specificity of 96%. However, the sensitivity and specificity obtained by Bezabih[16] were much lower: 88.5 and 81.5% respectively.

Twenty-seven cases were aspirated from enlarged lymph nodes. The most common diagnosis was of metastatic carcinoma (12 cases, 44.44%), followed by NHL (eight cases, 29.63%), tuberculosis (six cases, 22.22%), and one case of Hodgkin's lymphoma. Saikia et al.[17] found tuberculosis to be the most common lesion. Ten cases were confirmed by histopathological investigation, all of which were consistent with the cytological diagnoses; thus making us achieve a sensitivity, specificity, predictive value, and accuracy of 100%. These results were better than those recorded by other authors.

We aspirated two masses from the adrenals, one was an angiomyolipoma in a 48 year-old female and the other was a metastatic renal cell carcinoma in a 51 year-old male. Histological investigation was not done in either of the cases. USG-guided FNAC is thus highly safe and specific in the diagnosis of adrenal gland lesions which is in accordance with the findings of Nirag et al.[18]

In a few cases, the material obtained was scanty, especially in lymph node aspirates (due to their slippery and deep-seated nature). Cytological investigation was thus repeated in such cases.

The overall accuracy of the present study came out to be 96% (100% for benign, for 96% for malignant), sensitivity – 94%, specificity – 100%, predictive value – 100%, and efficiency of 96%.

Conclusions

USG-guided FNAC is an inexpensive, reliable, rapid, safe, and accurate procedure for the diagnosis of retroperitoneal masses. It was more accurate in diagnosing benign rather than malignant lesions. High accuracy in the present study (96%) could be achieved with the close co-operation of the clinician, radiologist, and pathologist.