We read with interest the article entitled “Imaging Approach to Pulmonary Infections
in the Immunocompromised Patient” by Grover et al.[1] We would like to add a “hypodense sign” (HyS) to the list of radiological findings
described by the authors. The HyS was described by Horger et al as[2] the presence of a central area of hypodensity seen on narrow window settings (width:
110–140 Hounsfield Units [HU]; level: 15–40 HU). This sign can be seen in consolidation
or nodule and can be appreciated on unenhanced scans, computed tomography pulmonary
angiography (CTPA), and contrast-enhanced scans. This sign has been reported to be
associated with invasive pulmonary aspergillosis, mucormycosis, and fusariosis.[3]
[4] The hypodense nodule sign has been described in the context of immunocompromised
patients. The underlying pathogenesis is infarction secondary to angioinvasion by
fungal elements.[3]
[4] This sign may be a precursor for forming a cavity.[2]
[5] Some studies have described the importance of hypodense sign in diagnosing invasive
mold disease ([Table 1]). Hence, it is a helpful sign in arriving at the diagnosis of invasive mold disease
with a sensitivity of 23% on high-resolution CT (HRCT) and 64% on CTPA, and a specificity
of 100% on HRCT and 98% on CTPA.[3] This sign can help to differentiate between bacterial and fungal diseases in immunocompromised
individuals.[2]
[3] This sign has also been described in some bacterial infections, particularly in
tuberculosis, i.e., a cavity filled with central mucous within or in case of a pulmonary
abscess; however, leukocytes play a vital role in abscess formation, and immunocompromised
individuals usually have neutropenia.[3]
[6] Hence, we would like to add the hypodense sign as a useful diagnostic sign in CTs
of immunocompromised individuals.
Table 1
Studies describing hypodense sign in immunocompromised patients
|
Study
|
Sample size
|
Type of scan
|
Patient population
|
|
Horger et al[2]
|
43
|
Unenhanced scan
|
Neutropenic patients
|
|
Sassi et al[3]
|
127
|
HRCT and contrast-enhanced CT
|
Hematological Malignancies
|
|
Qin et al[5]
|
25
|
CT chest with intravenous contrast and without intravenous contrast
|
Liver transplant patients
|
|
Stanzani et al[6]
|
44
|
Unenhanced scan and CTPA
|
Hematological malignancies
|
|
Schulze et al[7]
|
17
|
Noncontrast CT and volume perfusion CT
|
Hematological malignancies
|
