Pathological differentiation of suspected cases of pentastomiasis in China


Dr. K. C. Ma 1191-5C West Nanjing Road, Shanghai 200040, People's Republic of China. E-mail:


We report nine cases of suspected pentastomiasis from China, and propose that diagnosis of this rare parasitic disease should be made aetio-pathologically, subaetio-pathologically, and presumptively. In none of our cases' lesions we could find either a whole or part of an embedded nymph; hence, no aetio-pathologic diagnosis of pentastomid infection was established. In three cases, subaetio-pathologic diagnoses of pentastomiasis were made upon the discovery of a peculiar set of relics from lesions, namely two pairs of circumoral hooks of pentastomid from lesions. In one of these three cases, an extra scissors-like image indicating a longitudinal section of a hook of the embedded pentastomid nymph, probably Linguatula serrata, was found. In the other six cases, none of the relics of the aetiological agents were found, and our diagnoses were made presumptively by a series of relatively specific pathologic features, i.e. pearly lesions over the peritoneal surface of the abdominal cavity under the serosa of the intestinal wall or under the capsules of liver and spleen. They tend to be uniquely protuberant, sometimes linked by a short thin stalk to the surface. The hyalinization and calcification of these centrally caseated granulomatous nodules tend to be concentric and targetoid in appearance. Tuberculosis, the most easily confused condition, was easily ruled out pathohistologically. We believe that there is a need for presumptive pathologic diagnosis of human pentastomid infection not only in China, but worldwide.


There are two types of human pentastomiasis: one is visceral pentastomiasis, which is transmitted by ingesting the infective eggs of pentastomids into the human body which then acts as the intermediate host of these parasites; the other is nasopharyngeal pentastomiasis, which is transmitted by ingesting the infective nymphs of Linguatula serrata, and where the human body acts as an aberrant definitive host of these parasites.

The four Chinese cases of pentastomiasis reported in the literature (Faust 1927; Shin et al. 1990; Zhang et al. 1996, 1997; Li et al. 1998), as well as the nine suspected cases reported here, all belong to the visceral type. But in our nine cases, none of the specimens contained embedded nymphs. In view of such negative findings, Self (1972) and Self et al. (1972) stated that “Most biologists and pathologists would have little reason for suspecting a pentastome if all that remains of the nymph in an abcess or granuloma are fragments of cuticle”; and Hopps et al. (1971) as well as Ali-Kahn & Bowner (1972) found that pentastomes are liable to be “frequently unrecognized” from the lesions. Hence, we feel that the pathologic identification of human pentastomiasis, just as in some other infectious diseases, should not be limited to aetio-pathologic diagnosis by finding the entire nymph in the tissue section of the lesion, but should include both subaetio-pathologic diagnosis and presumptive pathologic diagnosis of this disease when the overall structure of the aetiological agent or even a fragment cannot be revealed. The subaetio-pathologic diagnosis of pentastomiasis indicates that the diagnosis is not based upon the identification of the entire aetiological agent (a complete embedded nymph of pentastomid) from the examined specimens, but is established merely by finding identifiable fragments of degenerated and/or calcified body structures of the embedded nymph (relics, such as the cuticular spines, sclerotized openings and/or the circumoral hooks, known as the pathognomonic hallmarks of pentastomiasis) remaining in the lesion(s). In such cases, the aetiological identification might not be traced to its genus and species, but is usually limited to `pentastomid'. The practice of pathologic diagnosis of pentastomiasis in China as well as in other countries of the temperate zone might be somewhat dissimilar to that reported from tropical countries, such as in Malaysia and Central Africa, where this infection is more common and encysted nymphs are found in autopsies remarkably often (Prathap et al. 1969; Meyers et al. 1976).

This report is based on the records of nine pathologically studied cases of suspected human pentastomiasis collected during the 1950s to 1980s in Shanghai and Chongqing. Our main purposes were to study and discuss the pathognomonic hallmarks of the subaetio-pathologic diagnosis, the criteria for presumptive pathologic diagnosis of this rare disease and also the crucial points for its differential diagnosis.

Case reports

Case 1

The pathologic diagnosis was pentastomiasis (by subaetio-pathologic diagnosis; caused probably by L. serrata), widely involving the small intestine, the mesenteric lymph nodes, pulmonary hilar lymph nodes, and Glisson's capsule of the liver; causing acute and chronic peritonitis and pleuritis, with widespread fibrinous and fibrous adhesions over the peritoneum and bilateral pleura, and complete intestinal obstruction of the lower segment of the ileum at the root of the mesentery because of intense fibrous adhesion, and severe generalized dehydration. Cause of death was an extraordinarily heavy pentastomid infection leading to acute and chronic peritonitis, widespread peritoneal adhesions, and complete intestinal obstruction.

A 7-year-old male native of Ningpo, Zhejiang province complained of paroxysmal pain in the abdomen and vomiting for 18 h. Past history revealed that he had had feverishness at the age of two which was diagnosed as `pulmonary tuberculosis', `pleurisy' and `peritonitis'. In the right lower quadrant of his abdomen there was marked resistance with borborygmi and low grade fever. The clinical diagnosis was acute appendicitis. Appendectomy was performed. His condition improved post-operatively until on the sixth day the paroxysmal abdominal pain with vomiting resumed together with marked borborygmi and periumbilical tenderness. Abdominal fluoroscopy discovered gradient liquid–air levels. Mechanical intestinal obstruction was then suspected and a second laparotomy performed. This revealed a large amount of yellowish exudate in the abdominal cavity; numerous protuberant pea to soy-bean sized caseous nodules 2–5 mm in diameter on the serosal surface of the small intestine; extensive fibrous adhesions between the loops of the ileum with formation of an internal fistula and an acute angle contracture–flexion at the end of the ileum, causing complete intestinal obstruction. After release of the intestinal obstruction and repair of the internal fistula a shortcut operation was performed. Several caseous nodules were removed for pathologic examination. The child's condition worsened and he died 6 h after the operation.

The post-operative diagnosis was tuberculous peritonitis, causing widespread adhesions of the loops of the ileum and an acute angle flexion at the end of the ileum and complete intestinal obstruction; severe generalized dehydration. The pathologic diagnosis of the biopsied caseous nodules confirmed fibrocalcified nodule of the intestinal wall (tuberculosis).

The postmortem examination was performed 12 h after death. The body showed signs of severe dehydration. Widespread fibrous and fibrinous adhesions between the loops of the ileum, the omentum and the parietal peritoneum were found. The small intestine as a whole was distended with air. Its serosal surface was markedly congested. A complete intestinal obstruction was found in the ileocecal region because of intense fibrous adhesion at the root of the mesentery. The mucosal surface of the colon below the obstruction as a whole was blackened. Other important findings were recorded as follows:

(1) Thirty-three protuberant sclerotic nodules over the serosal surface of the ileum, one in the jejunum. These were round, whitish, and pearly, with a diameter ranging from 2 to 8 mm, and different in consistency. Some hung over the surface with a thin and short stalk (Figure 1a). Extensive thready adhesions were associated with these nodules. Two band-like dense adhesions were found near the end of ileum at the root of mesentery. One of them was the point of acute angle obstruction in the ileocecal region. Histologically these nodules showed a typical fibrocalcified structure filled with amorphous eosinophilic and acellular debris, a calcification core surrounded by dense hyalinized fibrous tissue (Figure 3a). Extensive chronic inflammatory reactions were found mainly in the thickened serosa of the small intestine (Figure 3a).

Figure 1.

 (a) Case 1 (A1334) (Upper part): A short-stalked fibrocalcified nodule hanging over the serosa of the ileum. (Lower part): The cut surface of this nodule showing that the calcification centre is surrounded by dense fibrous tissue. (b) Case 2 (A4344): A protuberant pearly fibrocalcified nodule (in the centre) hanging over the emphysematous surface of the lung with a short stalk. Its diameter is 3 mm. Near the right margin as indicated by an arrow several `miliary tubercles' are seen.

Figure 3.

 (a) Case 1: An intraserosal fibrocalcified nodule with calcification in the centre forming an obvious pressure to the outer layer of muscularis. The serosa is greatly thickened because of the chronic inflammatory reaction. Hematoxylin–eosin stain 40×. (b) Case 2: The targetoid concentric configuration of the deposition of calcium salt found among the coagulative necrosis in a pulmonary hilar lymph node. Hematoxylin–eosin stain 144×.

(2) Fifty generally enlarged mesenteric lymph nodes and 18 pulmonary hilar lymph nodes measuring 7–20 mm in diameter contained similar sclerotic nodules of 2–8 mm in diameter, sharply demarcated from their neighbouring lymphatic tissue. Histologically, all were composed of fibrohyalinized capsules, caseation centres and calcification deposits, with peripheral chronic granulomatous inflammatory reactions with foreign body giant cells not of the Langhans type. In two of the largest pulmonary hilar lymph nodes with prominent caseous necrosis a number of morphologically specific calcified materials in sets were found in the centre of the lesions. Serial sections of five of these revealed circumoral hooks of pentastomid (Figure 6). Thereafter, all embedded and remaining lymph nodes with fibrocalcified nodules from the pulmonary hilar region and the mesentery underwent digestive fermentation to soften and clear fibrocalcified material to release calcified and non-calcified structures of the embedded agents (nymphs) other than the symmetrical structures in the mouth region. But none were found.

Figure 6.

 Case 1: A similar but somewhat more complicated group of calcified relics found from a caseated lesion in the pulmonary hilar lymph node. In contrast with Figure 4 they appear to be mainly composed of two pairs of circumoral hooks (arrow for the inner one; arrowhead for the outer one) with long and remarkably arciform fulcra. The inner paired hooks look more slender than the outer ones. A scissors-like calcified image, indicated by two larger arrows on the left, may be an approximate mid-longitudinal section of a hook barb (the upper larger arrow) and its shank (the lower larger arrow) coinciding with the hook shape of Linguatula serrata. The largest transverse diameter of this group is 92 μm. Hematoxylin–eosin stain 630×.

These calcified symmetrical structures in serial sections were compared with a typical nymph specimen of L. serrata in the Department of Parasitology, Shanghai Medical University (Qiu 1957) (Figure 4a,b). Although the `central mouth opening' was absent in the sections, the calcified symmetrical structures as a whole were morphologically equivalent to the mouth region of this nymph with two pairs of hooks and their associated fulcra (Figure 6). However, the fulcra are more arciform in appearance, possibly because of the process of calcification and postmortem sectioning (compare Figure 6 with Figure 4a,b ). The largest transverse diameters of these structures were 90–100 μm, consistent with the measurement of the mouth region of the nymph specimen of L. serrata. Hence, these calcified structures could only provide a morphological similarity to the mouth region of a pentastomid (either Linguatula or Armillifer), so that our diagnosis of this case could only be issued subaetiologically as pentastomiasis.

Figure 4.

 (a) Schematic drawing of the typical anatomical appearance of the two pairs of circumoral hooks with their fulcra in the mouth region of a nymph of Linguatula serrata, collected from Lanzhou, China. The largest transverse diameter between the two pairs of hooks of these specimens is 90–100 μm. The dotted ring in the centre is the central mouth opening. 130×. (b) The original slide specimen of this L. serrata showing clearly the archwise-disposed hooks of the outer pair, their long fulcra and the central mouth opening. Not stained 160×.

(3) There was no evidence of pulmonary tuberculosis (Ghon's complex) and intestinal tuberculosis, nor of miliary tuberculosis, tuberculous pleurisy and peritonitis.

(4) Dr John Riley, one of the referees of this paper, pointed out “a hollow hook barb and its shank” (a scissors-like image on the left with two larger arrows) within the calcified symmetrical structures in Figure 6, which looks like an approximate mid-longitudinal section of the hook of pentastomids with a longer barb, probably nymphal L. serrata rather than Armillifer sp. (Figure 6).

Case 2

The pathologic diagnosis was (1) squamous carcinoma of oesophagus and cardia of the stomach with lymphohematogenous metastases and cachexia; coupled with (2) pentastomiasis (by subaetio-pathologic diagnosis) with fibrocalcified nodular lesions widely involving serosa of transverse colon, splenic capsule, the pleural surface of both lungs as well as mesenteric and pulmonary hilar lymph nodes.

An 86-year-old male native of Shanghai died of cachexia because of carcinoma of oesophagus and cardia. The postmortem examination revealed numerous pearly sclerotic nodules measuring between 3 and 7 mm in diameter. Many of these nodules resembled miliary tubercles, but were remarkably protuberant, in some cases just dropping out with a slender stalk over the surface (Figure 1b). A set of symmetrical embracing relics was found in one taken from the anterior surface of the left upper lung (Figure 5), similar to that in Figure 6 (Case 1), but simpler and without the scissor-like image. It was embedded in the densely hyalinized collagenous tissue (Figure 5), its largest transverse diameter measuring 90 μm. In the fibrocalcified nodules of the pulmonary hilar lymph nodes, targetoid concentric circles were often seen in the centre of coagulative necrosis (Figure 3b). No other relic was found in any of the other nodular lesions.

Figure 5.

 Case 2: A group of calcified relics mimicking the pentastomid circumoral hooks with their long and remarkably arciform fulcra in two pairs (in contrast with Figure 4a,b; the inner pair is shorter, as indicated by an arrow on the left one). They were found from the serial sections of a pearly nodule over the surface of the patient's lung. The largest transverse diameter of this group is 90 μm. Hematoxylin–eosin stain 630×.

Case 3

The pathologic diagnosis was pentastomiotic myocarditis and pericarditis (by subaetio-pathologic diagnosis), leading to heart failure and death.

This was an autopsy consultation case of the Department of Pathology, Shanghai Medical University in 1962. A male adult died of heart failure with the clinical diagnosis of acute viral myocarditis. Histological examination of the heart disclosed granulomatous pericarditis and myocarditis (Figures 8 and 9). Within the granulomatous myocardial lesions many unidentifiable calcified relics, surrounded or phagocytosed by foreign body giant cells, were seen (Figure 9). One of these relics closely resembled a pair of curved hooks (Figure 10). Another set of relics was found (Figure 7), similar to those seen in the pulmonary hilar lymph nodes of Case 1 (Figure 6), and that in a nodule over the pleural surface of the lung in Case 2 (Figure 5), but without the scissor-like image in Figure 6.

Figure 8.

 Case 3: Pentastomid myocarditis showing myocardial fragmentation, myofibrillary hyaline degeneration and lysis with diffuse round cell infiltration. Hematoxylin–eosin stain 144×.

Figure 9.

 Case 3: Pentastomid pericarditis showing clumps of calcified unidentifiable relics of nymphal pentastomid, being surrounded by chronic granulomatous inflammation with many foreign body giant cells. Hematoxylin–eosin stain 144×.

Figure 10.

 Case 3: High power view of a focus of pentastomid pericarditis showing a group of calcified relics with appearance strongly suggestive of some dislocated `curved hooks' as illustrated in Figures 789. It is surrounded closely by foreign body giant cells. Hematoxylin–eosin stain 540×.

Figure 7.

 Case 3: A very similar structure of a group of calcified relics to those shown in 4Figures 4a,b, 5 and 6. It was found in a focus of pentastomid granulomatous pericarditis (as shown in Figures 9 and 10). This rather symmetrical structure is also believed to stand for the two pairs of circumoral hooks with their long and remarkably arciform fulcra. The shape of the right lower one indicated by an arrow is coinciding with a `curved hook'. The largest transverse diameter of this group is 90 μm. Hematoxylin–eosin stain 540×.

Case 4

The pathologic diagnosis was (1) cardiovascular syphilis and (2) pentastomiasis (by presumptive pathologic diagnosis), involving the serosa of small intestine, the capsules of liver and spleen.

A 53-year-old male native of Shanghai died of heart failure because of cardiovascular syphilis. During the postmortem examination many protruding `pearls' (< 1 cm in diameter) were found incidentally over the serosal surface of the small intestine and the capsules of liver and spleen with extensive adhesions to the diaphragm. Histological examination revealed neither the embedded pentastomid nymph nor pathognomonic hallmarks of pentastomiasis or any of the pathological signs of tuberculous infection. But in the protruding `pearls', characteristic concentric targetoid calcifications were found, each in a core of caseation with hyalinized capsule. They closely resembled those of Cases 1 and 2 (Figure 3a,b) and had the same distribution pattern. Hence, pentastomid infection was strongly suggested.

Case 5

The pathologic diagnosis was: (1) renal arteriolosclerosis and hypertension and (2) pentastomiasis (by presumptive pathologic diagnosis), involving the apical pleura of both lungs.

A 65-year-old male native of Shanghai died of uremia because of renal arteriosclerosis and hypertension. During the postmortem examination irregular pleural thickenings measuring about 1.5 × 5.5 cm were found on the apices of both lungs. They were composed of a number of remarkably protuberant pearly nodules (whitish and sclerotic) with an average measurement of about 3 × 4 × 2 mm (Figure 2a), quite different from the thickening produced by apical tuberculosis. Serial histological sections disclosed no foreign bodies (dislocated pentastomid cuticular spines, sclerotized openings or circumoral hooks), but highly laminated hyalinized tissue with calcification in the centre. Pentastomid infection of the apical pleura of both lungs was thus strongly suggested.

Figure 2.

  (a) Case 5: A remarkably protuberant hyalinized nodule over the apical visceral pleura is shown on the cut surface of the patient's lung. Similar nodules were found incidentally during the autopsy on the apices of both lungs. None of any foreign body or any relic of the pentastomid nymph was found by serial sections of these nodules (20×). (b) Case 2: Numerous fibrohyalinized protuberant nodular lesions of different sizes over the splenic capsule of the patient's enlarged spleen, many confluent into a patch (in the right lower corner).

Case 6

The pathologic diagnosis was: (1) acute haemorrhagic pancreatitis, (2) essential hypertension and (3) pentastomiasis (by presumptive pathologic diagnosis) involving the capsules of liver and spleen and the pleura of both lungs.

A 65-year-old male native of Chongqing died of acute haemorrhagic pancreatitis and hypertension. Numerous protruding pearly nodules (< 1 cm in diameter) were found on the capsules of liver and spleen and the pleura of both lungs during postmortem examination. Histological sections of these nodules revealed concentrically calcified circles (targetoid appearance) in hyalinized lesions, as in 3Figures 3a,b, found in Cases 1 and 2, respectively. No foreign bodies derived from degenerated or calcified cuticular spines, sclerotized openings, or circumoral hooks of embedded pentastomid nymph were found.

Cases 7–9

Surgical specimens were taken during abdominal operations of three patients: a 7-year-old boy in 1956, a 50-year-old male in 1959 and a 39-year-old male in 1960, in the Department of General Surgery, Zhong Shan Hospital, Shanghai Medical University. The leading surgeons incidentally discovered protruding round sclerotic nodules (< 1 cm in diameter), either over the serosa of the small intestine or over Glisson's capsule of the liver. All three surgeons suspected tuberculous peritonitis and asked for pathologic confirmation. The pathological diagnosis in all three cases was “protuberant fibrotic nodule with targetoid concentric circles of calcification in the centre, presumptively indicating pentastomid infection”.


Pentastomiasis is a rare parasitic disease in China. Based upon an approximate estimate from the autopsy records of the Department of Pathology, Shanghai Medical University, during 1946–81, only five of the 4344 autopsy cases were diagnosed as pentastomiasis (0.115%). The highest prevalences are recorded from autopsy records in Malaysia (45.4%) (Prathap et al. 1969) and central Africa (22.5%) (Meyers et al. 1976). It is believed that the incidence of this infection in China is similar to that reported from North America (Baird et al. 1988; Guardia et al. 1991).

Man is usually highly tolerant to pentastomid infections, and most of them are asymptomatic. The embedded pentastomid nymphs or their degenerated relics in the lesions are usually discovered incidentally at autopsy, surgery, by X-ray, ultrasonography or CT scan. However, based on our experience from these nine cases, we speculate that in China, these endoparasitic agents might disintegrate more quickly and thoroughly in vivo than in other endemic areas, even in an unusually massive infection as that reported in Case 1. Hence, a complete structure of encysted nymphs was only very rarely found in the lesions of pentastomiotic patients in China, remarkably different from Malaysia (Prathap et al. 1969), central Africa (Meyers et al. 1976) and Nigeria (Lindner 1965). From 1927 until 1997 only four such cases were recorded in China; two encysted nymphs of L. serrata were found in the margin of the liver of the patients, one in Peking (Faust 1927; Qiu & Chen 1999), the other in Naning (Li et al. 1998); the third (Shin et al. 1990) and fourth (Zhang et al. 1996, 1997) being cases of human armilliferosis agkistrodentis in Taiwan and Hangzhou, the first two instances of this disease to be documented.

In none of the nine cases reported here were embedded pentastomid nymphs found. Only in cases 1–3 calcified relics strongly suggestive of circumoral hooks of a pentastomid with their strikingly arciform fulcra in a symmetri cal set and a scissor-like image, indicating a longitudinal section of the calcified hook, could be identified (Figures 5–7). These findings are considered the pathognomonic indicators for the subaetio-pathologic diagnosis of pentastomid infection. The remaining six suspected cases, three autopsies and three surgical specimens, were presumptively diagnosed as pentastomiasis on the basis of their characteristic pathoanatomical and pathohistological features, but without direct evidence for subaetio-pathologic diagnosis.

Cases 1 and 3 were fatal and extremely rare conditions, supposed to be the 11th and 12th reported fatal cases of pentastomiasis in the literature (Wilson 1913; Sambon 1922; Cannon 1942; Manuwa 1947; Bouckaert & Fain 1959; Cagnard et al. 1979; Tiendrebeogo et al. 1982). The two documented causes of death of lethal pentastomid infection are intestinal obstruction because of extensive peritoneal adhesions (Sambon 1922; Qiu & Chen 1999) and meningitis because of subarachnoid infection (Bouckaert & Fain 1959). Our Case 1 is believed to be the fourth documented case dying of intestinal obstruction since the first report by Cannon (1942), the second by Manuwa (1947), and the third in 1959 by Bouckaert and Fain (1959). Our Case 3, with prominent pentastomiotic myocarditis and pericarditis, dying of cardiac failure, is probably the first documented in the literature.

The significance of the three varieties of pathologic diagnosis of pentastomiasis

Owing to the fact that the aetiological agents in vivo– pentastomid nymphs – are generally eliminated either partially or entirely from the lesions by the defensive measures of the host, this rare parasitic disease is liable to be undiagnosed or misdiagnosed pathologically. Therefore, we propose that the pathologic diagnosis of this disease should be practised as follows: (1) an aetio-pathologic diagnosis based on the finding of the entire or most of the encysted nymph from the lesions; (2) a subaetio-pathologic diagnosis based on the finding of the fragmented or dislocated, and calcified relics of the degenerated nymph from the lesions; (3) a presumptive pathologic diagnosis based purely on the pathoanatomical and pathohistological characteristics of the pentastomid infection. In the aetio-pathologic diagnosis the identification of the encysted nymph can usually be traced to its species, while in the subaetio-pathologic diagnosis identification may extend only to `pentastomid'.

Pathognomonic hallmarks of subaetio-pathologic diagnosis

In subaetio-pathologic diagnosis the dislocated and calcified cuticular spines, sclerotized openings and circumoral hooks are considered to be the three pathognomonic hallmarks of this infection (Tobie et al. 1957; Mendeloff 1965; Chitwood & Lichtenfels 1972; Baird et al. 1988; Guardia et al. 1991). Among them the opportunity of discovering cuticular spines in the histological sections ought to be greater than the latter because the former two are present all over the body of the nymph while the latter is located only circumorally. However, the calcified relics of the pentastomid `oral armature' possesses greater dimensions with more characteristic features than the spines (Figures 4a,b, 5–7, 9, 10). Among the chitinous cuticle structures of the embedded pentastomid nymphs, the most refractory element against degeneration and lysis, and the component most liable to be calcified is believed to be the circumoral hooks. Hence, we consider that the presence of these relics might be more prolonged than the other two. Nevertheless, in the cases reported by Mendeloff (1965) and in Case 2 reported by St Symmers and Valteris (1950) no circumoral hook was found, but only the spines; in the case reported by Baird et al. (1988) both the sclerotized openings and the cuticular spines were found, but not the circumoral hooks. By contrast (Cases 1–3) we found only the calcified symmetrical relics resembling circumoral hooks and their fulcra, not the spines, nor the sclerotized openings.

Furthermore, quite coincidentally, we have those three sets of calcified relics mimicking circumoral hooks and their long arciform fulcra to be sectioned nearly at a similar plane with similar symmetrical structures (Figures 5–7), which look entirely different from the illustrations shown by Meyers et al. (1976; Figures 12-1-5), by Prathap et al. (1969; Figure 3, by Chitwood and Lichtenfels (1972; Figures 11–13) and that by Kagei and Shichiri (1990; Figure 5). These different morphological appearances in the histological sections (Figures 5–7) are believed to be the outcome of different tangential planes of the circumoral hooks during sectioning, and probably they are the first series ever reported in the literature.

As to `a scissors-like relic' pointed out by Dr John Riley in Figure 6, we believe that it would be a further striking evidence in strengthening our suggestion of the calcified symmetrical structures to our subaetio-pathological diagnosis of Case 1 not only as pentastomiasis but caused probably by L. serrata. This scissors-like calcified relic looks like an approximate mid-longitudinal section of a hook with its narrower and longer barb obliquely disposed upwards (the upper larger arrow) and a much wider shank at its base (the lower larger arrow). Owing to this, barb is definitely longer than its shank, indicating a shallower barb curvature than that of Armillifer sp., L. serrata is strongly recommended (4Figure 4a,b; Faust 1927, Figures 3, 6 and 7; Rendtorff 1962, Figure 2; Riley & Spratt 1987, 1Figure 1d; Fain 1961, Figure 43). If the hook was sectioned in any other possible tangential plane, the distinction between L. serrata and Armillifer sp. would be hardly accessible. Most likely it would be a further exceedingly rare opportunity to have a scissors-like image of a dislocated hook of an embedded pentastome nymph to be sectioned together with a set of symmetrically arranged relics of circumoral armature at its cephalothorax region in different tangential planes (Case 1, Figure 6).

The presence or absence of cuticular spines is one of the main differential characteristics between the nymphs of L. serrata and A. armillatus (St Symmers & Valteris 1950; Tobie et al. 1957; Baird et al. 1988; Guardia et al. 1991; Qiu & Chen 1999), if they are found in the examined lesion, linguatuliosis is indicated, otherwise pentastomiasis would be appropriate for the subaetio-pathological diagnosis. As to the sclerotized openings, they could be found in the lesions of both linguatuliosis and armilliferiosis (Meyers et al. 1976; Baird et al. 1988).

Characteristic features of presumptive pathologic diagnosis of pentastomiasis and their combined effects with the establishment of subaetio-pathologic diagnosis

Cases 4–9 were presumptively diagnosed as pentastomiasis based on the following pathomorphologic peculiarities of this parasitic disease: the distribution pattern of lesions, their histological localization, and their characteristic features.

The peculiar distribution of lesions in this disease is the reflection of the route of invasion and migration of the endoparasites in the human body, known as `visceral larva migrans'. The swallowed infective eggs are hatched into larvae in the intestine; then, penetrating through the intestinal wall, and, generally, by way of lymphatic spread, become attached to the visceral peritoneum and/or pleura, over the surfaces of liver, intestine, spleen, lungs and into the mesenteric and pulmonary lymph nodes, where the larvae moult and develop into nymphs. This is usually followed by local encystment of the nymphs, nymphal migration because of massive infection and reinfection, and finally their death with release of a large amount of foreign protein. Upon delayed hypersensitivity, either an acute inflammatory reaction or a chronic granulomatous response with foreign body giant cells and prominent central necrosis (or both) develops, resulting as fibrohyalinized and fibrocalcified nodules in these organs and the related lymph nodes (Prathap et al. 1969; Hopps et al. 1971; Ali-Kahn & Bowner 1972; Self 1972; Self et al. 1972; Meyers et al. 1976).

These peritoneal or pleural lesions, as a rule, are localized superficially either under the serosa of the intestinal wall, or under the capsules of liver and spleen (Faust 1927; Fischer 1929; St Symmers & Valteris 1950; Meyers et al. 1976; Gardiner et al. 1984; Herzog et al. 1985; Baird et al. 1988), or over the pleural surface of the lungs. The pearly nodular lesions tend to be uniquely protuberant, and sometimes tend to be linked by a short thin stalk to the surface (Figures 1a, and2a,b), called `linguatula nodules' by St Symmers and Valteris (1950). The nodules usually measure less than 1 cm in diameter (2–3 mm in St Symmers & Valteris 1950); 3–8 mm in Herzog et al. (1985); 2–8 mm in our nine cases. Probably the unique protuberance of these lesions might be an indication of the process of `larva migrans effect' of the migrating nymphs (Self 1972; Self et al. 1972), which would be different from that produced by the non-migratory ova of Schistosoma japonicum. Furthermore, the hyalinization and calcification of these centrally caseated granulomatous nodules tends to be concentric or targetoid in appearance (Figure 3a,b). The mechanism of the formation of these concentric `rings' is not understood. Nevertheless, the numerous `pearls' over the peritoneal surface of the abdominal cavity together with the centrally located calcification can be the basis of the presumptive diagnosis of pentastomiasis by roentgenography (Lindner 1965), ultrasonography and CT scan.

We propose that the significance of the presumptive pathologic diagnosis of this disease should be emphasized, particularly in China and probably also in other countries of the temperate regions. The embedded nymphs and their relics are liable to degenerate and disintegrate entirely from the lesions in the majority of cases, which are mild, innocent and asymptomatic; thus, the aetiological agents of this disease used to be frequently unrecognized in tissue sections (Hopps et al. 1971; Ali-Kahn & Bowner 1972; Chitwood & Lichtenfels 1972). If the remaining relics could only provide inconclusive evidence for subaetio-pathologic diagnosis (for instance, as in Case 3 with only the finding as shown in Figures 9 or 10, without those shown in Figures 5–7), they would be well supplemented by the presumptive pathologic diagnosis of the same case. The subaetio-pathological and the presumptive pathological diagnoses of this disease can complement each other.

Pathological differential diagnosis of pentastomiasis

In the differential diagnosis of this disease tuberculosis is most frequently confused with pentastomiasis, apart from those easily distinguished parasites, such as the ova of S. japonicum, cysticerci, spargana, tissue-inhabiting arthropods (Meyers et al. 1976), and the anisakine larvae (Yokogawa & Yoshimura 1965), as in most of our reported cases (Cases 1, 2, 4, 5 and 7–9). However, by careful comparison, tuberculosis would be easily ruled out pathologically by the following remarkable features of pentastomiasis: the protuberance of the lesions over the visceral peritoneum and pleura; the concentric or targetoid appearance of the hyalinization and calcium deposition in the fibronodular lesions; the foreign-body giant cell reaction, instead of the Langhans type, in the foci of chronic granulomatous inflammation (Figures 1a,b, 2a,b, 3a,b and8–10).

The possibility of finding calcified circumoral hooks in the visceral lesions of human parasitic diseases arises only in the following three circumstances besides pentastomiasis: infection with Cysticercus cellulosae, Echinococcus granulosus, and Diptera larvae (myiasis). However, the hooklets of both cysticerci and echinococci are more numerous (25–50 in number) and much smaller than those of pentastomes, and those of Diptera larvae (maggots) have only one pair of mouth hooks each. These different characteristics might be helpful for differential diagnosis. When most parts of the aetiological agent have degenerated and disintegrated from the lesion, the morphological exhibition of those calcified hooks in histological sections might only provide some hints without any recognizable diagnostic characters. If a pathologist encounters such a case, the presumptive pathologic diagnosis of this disease would be very helpful for him to reach his final decision.


We wish to express our deep gratitude to Dr J. Riley and Professor S. Cairncross for their valuable comments and linguistic corrections, particularly to Dr Riley's remarkable observation of a hook barb and its shank of the suspected nymphal pentastomid in Figure 6. This article is dedicated to Professor Djeng Yan Ku, the founder of pathology in Shanghai Medical College, in remembrance of his guidance and encouragement for the study of autopsy cases of pentastomiasis in Shanghai in the 1950s and the 1960s.