Are all subcutaneous parasitic cysts cysticercosis

Abstract

We read with interest the letter 'Cysticercosis Diagnosed by Fine Needle Aspiration Cytology' by Agrawal et al.1 The authors stated that 'Cysticercus cellulosae diagnosed by fine needle aspiration is very unusual' and that 'the case is reported because of its unusual presentation and rarity.' A quick review of the literature2-5 suggests the reverse. The cytomorphology of cysticercosis has been described in minute detail, covering the entire range, from viable cysts through necrotic and calcified lesions.2 Agrawal et al1 saw 'classic scolices.' However, each Cysticercus has only 1 scolex.6 Multiple scolices characterize other cestode larvae found in humans, notably the larva (hydatid cyst) of Echinococcus granulosus, which bears more than a passing resemblance to Cysticercus. Both possess a bladder wall: a thin, membranous bladder wall in Cysticercus and a thicker, acellular, lamellated membrane surrounding the germinal layer in a hydated cyst. Protoscolices grow from this germinal layer, differentiating into broods and forming daughter cysts. A hydatid cyst that develops from a single egg may therefore contain thousands of scolices.6 While it is unusual, but not unknown, for hydatid cysts to occur in subcutaneous tissues, this is a common location for cysticercosis. Both cysts may yield clear, watery fluid on aspiration. The findings vary with the stage of evolution. Humans are accidental intermediate hosts of both parasites. Over months, the larva of Cysticercus dies, provoking the characteristic inflammatory response culminating in disintegration of the parasite. The viable cyst and the necrotic and calcified lesion all have distinctive cytomorphologic patterns.2 The most common finding in the clear fluid aspirated from viable cysts are delicate fragments of bladder wall with tiny, parasitic nuclei in a clear, acellular background. Aspirates of necrotic lesions may contain fragments of bladder wall, the invaginated portion, including calcareous corpuscles and detached, single hooklets. The inflammatory background ranges from acute inflammation with prominent eosinophils, through granulomatous inflammation with necrosis, to acellular necrosis without significant residual inflammation. Occasionally an entire scolex can be found in an inflammatory background. Single, detached hooklets and calcareous corpuscles may be the only recognizable remnants in aspirates of calcified cysts. Hydatid cysts live for many years and usually continue to grow unless the contents of the cyst die, presumably due to trauma or therapy, resulting in inflammation and disintegration of the parasite parts; those events are similar to those seen in cysticercosis. To the cytopathologist, the distinction lies in the cytomorphologic details. The scolex of Cysticercus is large, almost 1 mm in diameter. It has a rostellum and 4 suckers. The armed rostellum has 2 rings of alternating large and small hooklets measuring 170 (Figure 1A) and 130 \ub5m, respectively. The scolex is visible to the unaided eye and is easily recognized at scanning magnification (4\ua5) (Figure 1B). Finding an entire scolex in a fine needle aspirate is a rare event and, for reasons that are unclear, occurs in the inflammatory background of a partially necrotic cyst. In contrast, multiple scolices suspended in clear fluid are aspirated from viable hydatid cysts. In stark contrast to the scolex of Cysticercus, individual scolices of Echinococcus are small, albeit each with a rostellum and suckers (Figure 1C). The hooklets measure 22 and 40 \ub5m (Figure 1D). The rostellum can be detailed only at high magnification, as illustrated by Agrawal et al.1 On the basis of the evidence presented by Agrawal et al, their case is Echinococcus, not Cysticercus. The perception that a condition is rare or otherwise is closely linked to our ability to recognize what we see. At our institution we have seen cysticercosis transform from a rare to a fairly common diagnosis ever since we learned to recognize its various cytomorphologic manifestations. Our experience confirms endorsing the aphorism, 'What the mind does not know, the eye does not se