JPC SYSTEMIC PATHOLOGY

NERVOUS SYSTEM

February 2023

N-P12

 

Slide A: Signalment (JPC #1652892): Military working dog

 

HISTORY: This dog developed convulsions and ataxia.

 

HISTOPATHOLOGIC DESCRIPTION: Cerebrum, meninges: Focally elevating and expanding the meninges and compressing the adjacent gray and white matter is a larval cestode with a 2mm diameter invaginated scolex and a large, 4mm diameter bladder (cysticercus) surrounded by a connective tissue capsule. The capsule is composed of multiple layers of fibroblasts and collagen with rare lymphocytes, and blends with the meninges. The bladder wall is characterized by an up to 20 µm eosinophilic tegument surrounding spongy parenchyma with many embedded, oval, 10 x 30 µm, basophilic to clear, calcareous corpuscles. Multiple sections of sucker are visible within the scolex.  In the adjacent compressed gray matter and focally extending into the white matter, there is mild vacuolation (spongiosis) and dissolution of the neuropil (compression atrophy); few neurons with hypereosinophilic, shrunken, angular cytoplasm and pyknotic nuclei (neuronal necrosis); few reactive astrocytes with abundant eosinophilic cytoplasm (gemistocytes); and few swollen, degenerate axons within dilated myelin sheaths (spheroids).

 

MORPHOLOGIC DIAGNOSIS: Cerebrum, meninges: Cysticercus, focal, with gray and white matter spongiosis, neuronal necrosis, and gemistocytosis, breed not specified, canine.

 

ETIOLOGIC DIAGNOSIS: Cerebral cysticercosis

 

ETIOLOGY: Cysticercus cellulosae (larval stage of Taenia solium)

 

CONDITION: Cysticercosis

 

Slide B: Signalment (JPC #2026219): 2-year-old Corriedale ram

 

HISTORY: This ram was circling, with a head tilt, had a peculiar high-stepping gait, was grinding its teeth, and had an aversion to flocking behavior. He was one of several similarly affected sheep examined in Peru.

 

HISTOPATHOLOGIC DESCRIPTION: Brainstem: Multifocally elevating and expanding the meninges and minimally compressing the subjacent neuroparenchyma are few variably sized connective tissue capsules that each surround a single fluid-filled bladder that contains multiple larval cestodes (coenurus) characterized by up to 700 µm diameter invaginated scolices that often contain one or two suckers and a rostellum with refractile, chitinized hooks. The bladder wall is characterized by an up to 400 µm thick eosinophilic tegument surrounding spongy parenchyma with many embedded, oval, 10 x 30 µm, basophilic to clear, calcareous corpuscles. The meninges and connective capsules are infiltrated by numerous nodular aggregates and scattered inflammatory cells composed of varying numbers of neutrophils, lymphocytes, plasma cells, eosinophils, macrophages, multinucleate giant cells (foreign body and Langhans type), abundant eosinophilic cellular and karyorrhectic debris (necrosis), and many congested blood vessels. There are multifocal regions within the meninges that have loss of differential staining and retention of architecture (coagulative necrosis). Multifocally within the meninges, there are granulomas up to 700µm in diameter characterized by a central zone of necrosis surrounded by a concentric rim of epithelioid macrophages, bounded by a layer of numerous lymphocytes, plasma cells, and scattered eosinophils, which is further bounded by few fibroblasts on a thin collagenous matrix, and few multinucleate giant cells. Focally, a nerve rootlet is minimally infiltrated by few lymphocytes and plasma cells. Scattered macrophages and multinucleate giant cells frequently contain an intracytoplasmic brown globular pigment (hemosiderin). Multifocally, in areas of compressed white matter, lymphocytes and plasma cells expand Virchow-Robin space (perivascular cuffing) and affected blood vessels have hypertrophic endothelium (reactive). Multifocally, there is mild vacuolation of the parenchyma (spongiosis), and gliosis.

 

MORPHOLOGIC DIAGNOSIS: Brainstem: Meningitis, granulomatous and lymphoplasmacytic, diffuse, severe, with spongiosis, gliosis, perivascular cuffing, and multiple meningeal coenuri, Corriedale, ovine.

 

CAUSE: Coenurus cerebralis (larval stage of Taenia multiceps)

 

ETIOLOGIC DIAGNOSIS: Meningeal coenurosis

 

CONDITION: "Gid" or "Sturdy"

 

GENERAL DISCUSSION:

• Tapeworms belong to the class Cestoda of the phylum Platyhelminthes; the two orders of veterinary interest are Pseudophyllidea and the Cyclophyllidae

• The order Pseudophyllidea has two genera of veterinary interest:  Diphyllobothrium and Spirometra; most require two intermediate hosts and are associated with aquatic food chains

• 1^st intermediate host: copepod
• 2^nd intermediate host: amphibian, fish, or reptile

• The order Cyclophyllidae has five families of veterinary interest Taeniidae, Mesocestoididae, Anoplocephalidae, Dipylidiidae, and Hymenolepididae; most only require one intermediate host and are associated with terrestrial food chains

• Intermediate host: mammal or arthropod

• Adult tapeworms inhabit ducts of the liver and pancreas or the gastrointestinal tract; flattened, segmented organisms with sequentially maturing hermaphroditic proglottids, forming an elongate strobila; attach to host via a scolex which usually has four suckers +/- a rostellum and hooks
• Fully developed second stage larvae in the family Taeniidae consist of a fluid filled bladder with one or more scolices (often called a bladder-worm) surrounded by a connective tissue capsule formed by the vertebrate intermediate host
• The larvae (Cysticercus cellulosae) of the human tapeworm, Taenia solium occur primarily within cardiac and skeletal muscle (masseter muscle, tongue, shoulder muscle) of pigs and may cause neurological disease in swine, humans, and occasionally dogs
• The larvae (Coenurus cerebralis) of the canine tapeworm, Taenia multiceps, produce neurological disease in sheep and other animals
• Cysticercus: A single fluid-filled bladder with one invaginated scolex and neck
• Strobilocercus: Late in larval development of cysticercus, scolex evaginates, elongates, and segments in the intermediate host, resembling a tapeworm 
• Coenurus: A single fluid-filled bladder with many scolices in clusters on the inner wall

 

PATHOGENESIS:

Cysticercus cellulosae/Taenia solium:

Coenurus cerebralis/Taenia multiceps:

 

LIFE CYCLE:

Cysticercus cellulosae/Taenia solium:

• Taenia solium (adult tapeworm) resides in the human small intestine (definitive host); larval forms most likely in dogs, sheep, and pigs
• Swine become infected by ingestion of tapeworm eggs from human feces
• In the pig, the outer shell of the egg is digested within the stomach and an oncosphere hatches; oncosphere penetrates the pig's intestinal blood vessels and enters the systemic circulation
• Most cysticerci (larvae) migrate to skeletal and cardiac muscle of the pig (intermediate host) but may migrate to CNS (i.e. neurocysticercosis); humans may act as intermediate hosts if they ingest eggs and then cysticerci can form within the brain, viscera, and connective tissue
• Adult tapeworms develop when humans are infected by eating inadequately cooked pork containing cysticerci

Coenurus cerebralis/Taenia multiceps:

 

TYPICAL CLINICAL FINDINGS:

Cysticercus cellulosae/Taenia solium:

• No clinical signs in swine if located within striated muscle
• Neurological signs if located within the CNS

Coenurus cerebralis/Taenia multiceps:

 

TYPICAL GROSS FINDINGS:

Cysticercus cellulosae/Taenia solium:

Coenurus cerebralis/ Taenia multiceps:

• Purulent meningoencephalitis, and tortuous yellow to red tracts within CNS parenchyma during the migratory phase
• Expansile coenuri may develop anywhere in the brain and spinal cord
• Space occupying 4-5 cm diameter cysts but may be larger, with translucent wall and thick clear fluid, in the CNS later in infection (referred to as “gid” or “sturdy” at that point) most commonly present near the surface of parietal cortex of cerebrum but may be anywhere in brain or spinal cord; hydrocephalus and atrophy of adjacent neuroparenchyma

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Cysticercus cellulosae/Taenia solium:

• Cysticercus (larva) has a single fluid-filled bladder with one scolex
• The cysticercus has a tegument, parenchyma, calcareous corpuscles, no internal organs, suckers on the scolex and rostellar hooks
• Little to no inflammation in striated muscle of pigs if cysticercus is alive
• Granulomatous inflammation and mineral if dead; then absorbed by the body
• Cysticerci are primarily found within the striated muscle of pigs and less commonly in the CNS

Coenurus cerebralis/Taenia multiceps:

• Coenurus has a single fluid-filled bladder with multiple scolices
• The coenurus has a tegument, parenchyma, calcareous corpuscles, no internal organs, suckers on the scolex and a rostellum with chitinized hooks
• During migration, there is coagulative and liquefactive/lytic necrosis / malacia, hemorrhage, degenerate granulocytes, histiocytes including giant cells, mononuclear cells, and a fibroblastic capsule contributed by the host; reaction / inflammation may be minimal
• Disruption and destruction of tissue leads to microcavitation and gemistocytes may be present in older lesions
• Later, expansion of the coenurus causes neural tissue compression to the point of obliteration and overlying bone may be thin or perforated

 

DIFFERENTIAL DIAGNOSIS:

Cestode larvae in the CNS of cattle/small ruminants:

• Cysticercus bovis rarely invades the nervous system (also no rostrellar hooks)
• Echinococcus granulosus is differentiated by the presence of a unilocular cyst with a brood capsule and hydatid sand (protoscolices); dog-sheep life cycle

 

COMPARATIVE PATHOLOGY:

• Multiple wildlife and domestic species can be affected
• Goats: Coenuri also occur in other organs, beneath the skin and within muscle
• Cats: Accidental intermediate host for Taenia serialis; cerebral coenuri
• Rodents: Fibrosarcomas develop from hepatic cysts of Cysticercus fasciolaris (D-P22), larval stage of Taenia taeniaeformis (cat tapeworm)
• Recent report of unusual presentation of disseminated Hymenolepis nana in a ring-tailed lemur; the appearance was different from cysticercoids and intestinal adult cestodes described in typical H. nana infections in other species, lacking characteristic calcareous corpuscles, scolices, proglottid segmentation, reproductive or digestive organs; serpiginous parasites were found in the liver and lung, lined by a thin tegument, filled with lightly eosinophilic fibrillar stroma, and numerous, round basophilic cells (Vet Pathol 2022).

 

 

 

 

 

REFERENCES:

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