Infectious Disease Pathology
Case 1 -
Royal Jubilee Hospital
Click on each slide thumbnail image for an enlarged view
A 35 year old woman, 20 pack-year smoker, resident of Comox, Vancouver Island, presented with
pleuritic chest pain. The pain came and went in multiple areas on both sides of the chest. There was no
cough, hemoptysis or constitutional symptom and she felt well. Chest X-ray and CT showed multiple
nodules in both lung fields resembling "metastases, infection or, less likely, infarcts" but no hilar or
mediastinal adenopathy. An attempt at needle biopsy failed and a bronchoscopy with washings and
transbronchial biopsies was negative. A video-assisted thoracoscopic biopsy yielded a wedge of lung
containing a 2.3 cm nodule which had a yellowish cut surface. The surgeon divided the tissue sending
some to histopathology and some to microbiology.
Case 1 - Figure 1 - Wedge resection of lung (low power), showing a necrotizing granuloma.
Case 1 - Figure 2 - Wedge resection of lung (intermedicate power), with yeast cells visible in the areas of necrotizing granuloma
Case 1 - Figure 3 - Wedge resection of lung (high power), encapsulated yeast in area of necrosis. The fungi are round or elliptical with thin eosinophilic walls and a surrounding capsule or fuzzy zone and large clear halos.
Case 1 - Figure 4 - Mucicarmine stain - Wedge resection of lung, stain shows the mucinous capsules surrounding narrow-necked budding yeast consistent with Cryptococcus.
The section shows a necrotizing granuloma in which fungal yeast cells are readily visible. The fungi
are round or elliptical, with thin eosinophilic walls, a surrounding capsule or fuzzy zone and large
clear halos. Mucicarmine staining confirmed the mucinous capsules. These features are diagnostic of
Cryptococcus. The granuloma shows palisaded histiocytes around the necrotic
zone and organisms are present both within the macrophages and free in the necrotic zone. Outside the
granuloma are abundant foamy histiocytes, lymphocytes and plasma cells. The necrotic zone retains the
alveolar architecture and is not "caseous" or structureless.
Comment: This is a typical case of cryptococcal granuloma. I choose this
case to illustrate the foamy macrophages because they can be so abundant as to be mistaken for clear cell
carcinoma at frozen section. In our series (see below) foamy histiocytes were present in 11 of the 17
open lung biopsies and they were abundant in five cases (29%). When not abundant, foamy macrophages
formed part of the palisaded granulomatous lining which was composed of eosinophilic epithelioid
histiocytes in most cases.
Antifungal treatment resulted in rapid shrinkage of the
pulmonary nodules and return to normality.
Histopathology of Pulmonary Cryptococcosis
The diagnosis of pulmonary cryptococcosis is made either by morphologic recognition of the organisms
or by culture. FNA of lung is an effective diagnostic tool for cryptococcus.
A variety of
other specimen types are also used – endobronchial or transbronchial biopsies, open lung biopsies or
bronchoalveolar washings. The host reaction depends on the immunologic competence of the host and the
presence of a capsule around the organism. There may be no reaction at all in anergic subjects so that
AIDS patients may show vast numbers of cryptococci in the interstitium with little or no
In immunocompetent patients most reports concern single cases and it has not
been possible to study the time-course of the histological reaction to C.
neoformans. A mixed suppurative and granulomatous reaction or a pure granulomatous reaction with
varying necrosis is described.  Primary pulmonary cryptococcosis may be associated with
granulomas in hilar lymph nodes.  Non-encapsulated strains elicit an initial strong
suppurative response and later a suppurative granulomatous reaction.
The largest series reported to date, 36 patients, is an autopsy series from Johns Hopkins in the
period 1936 to 1983, which is by its nature highly selected for severity, although not all deaths were
due to the fungus.  The patients ranged in age from 2 to 89 years (mean, 49 years); all but
three patients had underlying debilitating diseases and 23 patients had received steroids and/or
chemotherapy. In 25 patients (69 per cent) cryptococcosis was a major factor contributing to death,
through pulmonary disease in ten, systemic involvement in seven, and central nervous system disease in
eight. In 15 patients (42 per cent) Cryptococcosis was diagnosed clinically.
Four morphologic patterns
|1.||One or more peripheral pulmonary granulomas in seven patients (19 per cent).|
|2.||Granulomatous pneumonia in nineteen patients (53 per cent), with intra-alveolar proliferating organisms and varying degrees of inflammatory response, which, when present, ranged from acute inflammation to diffuse intra-alveolar granulomas with giant cells.|
|3.||In seven patients (19 per cent) organisms were present diffusely within alveolar capillaries and interstitial tissues, and reactions ranged from little or no inflammation with numerous organisms to few organisms with miliary granulomas.|
|4.||In three patients (8 per cent) both intra-alveolar and intravascular organisms were present in massive numbers, and the primary route of infection was uncertain. The prominence of vascular invasion in these last two categories is of interest because of the tendency for Cryptococcus to disseminate to the meninges even in immunocompetent hosts.|
A recent series of 11 cases of pulmonary cryptococcosis (7 immunocompromised, 4 immunocompetent) found
that pulmonary nodules, either solitary or multiple, were the most common CT finding, present in 10/11
cases.  Discrete zones of ground glass attenuation on CT were seen surrounding nodules or
adjacent to nodules and corresponded to airspace accumulation of foamy macrophages and edema
|1.||Coccidioidomycosis is a granulomatous inflammatory process caused by a dimorphic spherical yeast measuring 30-100 micrometres with a "double-walled" capsule within which are numerous endospores. Yeasts are seen in giant cells and necrotic tissue, and stain with GMS and PAS but not with mucicarmine.|
|2.||Blastomycosis is caused by a dimorphic spherical yeast measuring 6-15 micrometres wide with a thick capsule and characteristic broad-based budding creating a dumbbell shape. The yeast is seen in giant cells and necrotic tissue, stains with GMS and PAS but negative or only weakly positive with mucicarmine. Mucosal surfaces may show pseudoepitheliomatous hyperplasia of the surface epithelium in reaction to the infection.|
|3.||Histoplasmosis is a dimorphic oval-shaped, yeast measuring 3-5 micrometres in diameter with a single nucleus that buds via a narrow base. It has a surrounding clear space, is typically seen in clusters within macrophages and stains with GMS and PAS but not with mucicarmine.|
The Recent Emergence of C. neoformans var gattii on Vancouver Island
There are two varieties of Cryptococcus, C. neoformans var. neoformans (CNVN) and C. neoformans var gattii (CNVG), and four serotypes (A, B, C, D). CNVN may be serotype A, D or AD
whereas CNVG is serotype B or C. A new endemic focus of CNVG serotype B infection on Vancouver Island
began around early 1999 and continues today. Previously, CNVGhas been geographically restricted to
certain tropical and subtropical regions. It has been well-studied in Australia and Papua New Guinea
where it more commonly causes disease in immunocompetent individuals than does CNVN. In Australia it is
associated with eucalyptus trees. The strain of CNVG on Vancouver Island is similar to one of the
Australian strains by DNA studies. The newly endemic region affects primarily the eastern coastal region
of Vancouver Island, which includes the main populated areas on the island.
Seventy five human cases were confirmed from January 1999 up to July 2003. The rate in humans is
approximately 2.7 cases per 100,000 population per annum, which is five times less than the rate of
serious injury in motor vehicle accidents, but about 27 times the incidence rate observed in endemic
areas in Australia. Many patients are smokers but a case-control study has not shown a statistical
increase in risk attributable to smoking. Two thirds of patients have no evidence of underlying
immunodeficiency, but about 25% were taking corticosteroids in doses exceeding 20 mg per day and
altogether, about a third of patients have some form of immunodeficiency. The human cases to date have
been predominantly respiratory but one case in four has meningitis. There have been fatalities.
The cause of the outbreak is unknown. Could it have been introduced by an infected exotic pet or
plant? Is climatic change involved? It is unlikely we will ever know how the infection arrived here.
Climatically, there has been a mean rise of winter temperatures at Nanaimo of two degrees over the past
Targeted sampling of trees, air and soil from the vicinity of where affected patients live, has
identified the organisms. Once an initial positive tree is identified, air and soil samples are taken
outward in concentric circles. Positive trees have been identified from Victoria to Parksville. The
positive trees are Douglas fir, Garry oak, Alder and Maple. Arbutus trees were first suspected as they
are relatives of Eucalyptus trees which were implicated in former outbreaks of C.
neoformans var gattii in Australia and Africa but these trees were
initially negative although some have given positive samples since 2002. Known positive trees continue
to be positive although not all replicate samples are positive in winter. Air concentrations are lower
in the winter and begin to increase in April. The highest air counts have been at Rathtrevor beach in
summer. Soil sample positives may decrease as air sample levels increase. Soil samples around an index
tree may be high near and far from the tree. In Duncan and Victoria, certain trees have been positive
for both serotypes A and B since September 2002.
The present outbreak affects animals, both domestic and wild, terrestrial and aquatic. Six Doll's
porpoises that were found dead have proven positive over the past four years and 4 of these were found in
the Strait of Georgia. Domestic cats and dogs, ferrets and other animals including such exotics as a
tapir have also been affected. Animals present with head or neck nodules, lymphadenopathy, nasal and
pneumonic signs. Diagnosis is made by cytology mainly. Some of the animals are being followed with
Cryptococcus antigen titre during treatment with fluconazole. Like the
humans, half of the animals had predisposing conditions that may have lowered their immunity. Many of
the animals had traveled to Central Island (Parksville-Namaimo) but not all did.
Histopathology of the recent Vancouver Island cases
Before the present outbreak cryptococcal lung infection was rarely seen on Vancouver Island. In our
histopathology files from 1999 to the present we have had 45 cases, 19 lung biopsies (17 wedge, two
transbronchial), 2 autopsies and 24 cytologic specimens, (FNAs, sputa or bronchial washings). One
autopsy was a fatal meningitis; the other was a cryptococcal pneumonia in a cirrhotic woman.
Lung biopsies were removed by thoracoscopic-assisted biopsy. Most were submitted for rapid diagnosis.
They consisted of lung wedges containing one or more firm nodules with a brown or yellow, often mucoid
appearance on cut surface. In many instances the diagnosis was established by examination of a scrape
smear or imprint from the cut surface. In most cases cultures were not successful from these cases.
Histologically, all of the wedge-biopsied nodules showed a central necrotic zone or zones in which the
ghosted outlines of alveoli were discernible. Organisms were usually readily visible in the necrotic
zone, but not always numerous. The necrotic zone was delineated by macrophages, sometimes palisaded and
eosinophilic but sometimes foamy. The organisms were usually confined to the necrotic zone. Most cases
showed a palisade of eosinophilic macrophages surrounding the necrotic area, and a further thin layer
containing a mixture of lymphocytes, plasma cells and fibroblasts. As mentioned above, foamy histiocytes
were present in 11 of the 17 open lung biopsies and they were abundant in five cases (29%) forming
collections outside the granuloma and filling the air spaces. At frozen section, the foamy macrophages
were misdiagnosed once as clear cell carcinoma but raised the question of a clear cell carcinoma in the
mind of the pathologist on other occasions particularly if the necrotic zone were not included in the
One case showed several tiny foci of necrosis and a mixed response of macrophages, eosinophils,
lymphocytes and plasma cells. The fungi in that case were not localized to the centre of the lesion but
scattered throughout the macrophages. One case of Cryptococcus infection occurred coincidentally with a
On immunostaining with monoclonal antibodies provided by Dr Thomas Kozel,  seventeen
histologically identified cases were confirmed as var. gattii at the time
There is a new epidemic focus of CNVG on Vancouver Island that
presents as pneumonitis or meningitis, sometimes after a very short exposure during a visit to the
island. Physicians in North America, and indeed worldwide, need to be aware of this risk in people who
have traveled to the island.
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