Detection of parasite by fine-needle aspiration cytology on unstained smear

QUESTION

Identify the parasite

1. Echinococcus

2. Cysticercus cellulosae

3. Wuchereria bancrofti

4. Enterobius vermicularis.

Answer

The correct cytological interpretation is

b. Cysticercus cellulosae.

EXPLANATION

Microscopic examination revealed the bladder wall fragment of cysticercus appearing as a granular, loose fibrillary sheet-like structure, partially obscured by a knobby undulating layer comprising tegument, and subtegument, which could be very well-identified in the unstained smears [Figure 1a]. Thereafter, smears were stained with MGG, which verified the presence of bladder wall of cysticercus comprising parenchyma partly covered by tegument and subtegument, as attested to by the presence of numerous blue nuclei. The folds were better visualized in the unstained preparation, being largely obscured by the numerous nuclei present in the subtegument [Figure 1b]. Other areas of the smear also revealed bladder wall fragment with blue nuclei [Figure b and c].

DISCUSSION

Cysticercosis is a parasitic disease caused by the larval stage of Taenia solium (Cysticercus cellulosae). The disease is more common in endemic areas of Central and South America, India, China, Southeast Asia, and subSaharan Africa.^[1] Humans acquire this parasite by drinking contaminated water or by eating uncooked vegetables infected with eggs.^[2,3] Consumption of raw vegetables such as cabbage, radish, and carrots has also been known to cause the disease.^[3] Subcutaneous or intramuscular palpable parasitic nodules are commonly due to cysticercosis and it is difficult to differentiate them from the more commonly encountered benign mesenchymal tumors and lymphadenitis on physical examination alone.^[4] Hence, cytologic diagnosis of cysticercosis is often a minor surprise for the referring clinician. FNAC is a simple, sensitive, cost effective, and rapid diagnostic tool for evaluation of any superficial palpable lump at various sites in the body. Demonstration of bladder wall fragment, hooklets, or calcareous corpuscles confirms the diagnosis of cysticercosis.^[5] The bladder wall has three layers; from outside inward they are tegument, subtegument, and parenchyma. When present separately, the parenchyma is characterized by fibrils, and when in continuity with that of entrance canal, few calcareous corpuscles may be seen.^[6] In our case, fluid was aspirated and cytology revealed a flat fragment with a somewhat fibrillary and granular part (parenchyma) in association with an undulating/folded (tegument and subtegument) area which evoked strong suspicion of cysticercosis in the unstained air dried smear. It is speculated that hooklets would also lend themselves to easy detection in unstained smears.

On cytology, cysticercosis can be differentiated from other parasite. In Echinococcus, the bladder wall is thick and laminated, while, it is thin and membranous in cysticercosis. Multiple small scolices are seen in Echinococcus, whereas single scolex is seen in cysticercus. In coenurus, multiple protoscolices are seen, which can be distinguished from the cysticercus, which have a single scolex.^[7] Microfilaria or of Wucheria bancrofti can be easily distinguished from cysticercus, based on the characteristic cytomorphology, that is, sheathed larvae with tail-tip free from nuclei.^[8]

Recognition of cysticercus on unstained smears is of some importance as numerous smears may be generated from the aspirated fluid, only a minority of which may harbor the diagnostic parasite fragments. Selection of appropriate smears for staining is crucial, if non-diagnostic reports are to be curtailed.

ADDITIONAL CONTINUING MEDICAL EDUCATION QUESTIONS

1. Following statement is true regarding cysticercosis

   1. Is caused by larvae of Taenia solium

   2. “Embryonated eggs” are consumed by human host in drinking water or with vegetables as accidental intermediate host

   3. Disease most commonly involves subcutaneous and muscle tissue, followed by brain and eye

   4. All of the above.

   Answer is d.

2. For the life cycle of taenia solium, the intermediate host is

   1. Dog

   2. Sheep

   3. Pig

   4. Horse.

   Answer is c.

3. The aspirate of cysticercosis can reveal which of the following

   1. Fragments of bladder wall

   2. Scolex and hooklet

   3. Calcareous spherules

   4. All of the above.

   Answer is d.

4. Which of the following statement is true regarding the cytomorphological feature of cysticercosis

   1. Size of the hooklet is 15–40 microns

   2. Bladder wall is thin and membranous

   3. Multiple small scolices are observed

   4. No inflammatory response is seen.

   Answer is b.

SUMMARY

Fine-needle aspiration has a pivotal role in evaluating subcutaneous nodules caused by cysticercosis. Although stained FNA smears reliably demonstrate cysticercosis, rapid on site evaluation of unstained smears can also permit confident cytodiagnosis, if the cytologist is familiar with it.