Orbital Fat Density as a Diagnostic Tool in Pre-Septal and Orbital Cellulitis

Figures & data

Figure 1. Intraconal orbital fat density as measured in the axial equator plane in a patient with right periorbital cellulitis. The text in the yellow font is automatically extracted from the manually selected area delineated by the yellow surrounding line. AR (area): 26.4 mm² represents the surface, VA (value): −68 represents the mean hounsfield units (HU) in that area, SD (Standard Deviation): 24.74 represents the standard deviation, and range: −99 to − 3 represents the HU range in that area. The HU were measured for each study participant in 6 separate spaces of the CT scans (nasal and temporal at the axial equator plane, one section above and one below).

Table 1. Demographics and clinical presentation of 57 patients with a final diagnosis of periorbital cellulitis (POC) or orbital cellulitis (OC). The groups differ in concomitant sinusitis (being higher in the OC Group).

Variable		POC n = 15	OC n = 42	P Value
Age		19.7 ± 16.6	15.4 ± 21.2	NS^a
Gender	M:F	10:5 (67%:33%)	33:9 (79%:21%)	NS^b
Sinusitis (any)	Yes:No	4:9 (31%:69%)	28:13 (68%:32%)	0.02^b
Fever	Yes:No	4:7 (36%:64%)	12:29 (29%:71%)	NS^b
White blood cell count (K)		11 ± 8	16 ± 5	NS^a
CRP blood test result		48 ± 61	68 ± 59	NS^a
Surgical intervention	Yes:No	0:15 (0%:100%)	6:36 (14%:86%)	NS^c
Hospital stay, days		6 ± 5	8 ± 3	NS^a

Values are given ± standard deviation unless indicated otherwise.

NS = non-significant; CRP = C-reactive protein.

^aIndependent samples Mann-Whitney U-test between the POC and OC groups.

^bChi-square test. ^cFisher’s exact test.

Table 2. Intraconal fat density measured by hounsfield units on Contrast-enhanced Computerized Tomography (CT) in 57 patients with periorbital or orbital cellulitis. Measurements were taken on Axial CT Scan Views and obtained in 6 locations per Patient^.a.

Variable	Involved side	SD	Non-involved side	SD	P Value*
Nasal medial	−37	27	−58	19	<0.001
Nasal superior	−38	25	−58	17	<0.001
Nasal inferior	−40	27	−58	22	<0.001
Temporal medial	−66	13	−68	12	0.1
Temporal superior	−66	13	−69	11	0.04
Temporal inferior	−66	14	−68	12	0.2
Mean	−52	17	−63	13	<0.001‡

SD = standard deviation.

*.Paired samples t-test.

‡.Significant values are in bold. ^aAt the horizontal equator of the globe (“medial”), one layer above (“superior”), and one layer below (“inferior”). The values were higher in the involved orbit in most views.

Table 3. Difference of Intraconal Fat Density between the nasal and temporal aspects of the orbit as measured by computerized tomography (CT) in 57 patients with periorbital cellulitis or orbital Cellulitis^.a.

Variable	Compared areas	HU	P Value
Involved orbit	NM – TM	29	<0.001
	NS – TS	27	<0.001
	NI - TI	25	<0.001
	Mean N – Mean T	27	<0.001
Noninvolved orbit	NM – TM	11	<0.001
	NS – TS	12	<0.001
	NI - TI	10	<0.001
	Mean N – Mean T	11	<0.001

HU = Hounsfield Units; N = nasal, T = temporal, M = medial, S = superior, I = inferior.

*Paired samples t-test.

Significant values are in bold.

^aMeasurements were taken on axial CT scan views and obtained in 6 locations per patient: at the horizontal equator of the globe (“medial”), one layer above (“superior”), and one layer below (“inferior”).

Figure 2. Orbital fat density and alteration in diagnosis from initial to final visit in 57 patients with peri-orbital cellulitis (POC) or orbital cellulitis (OC(. Left, involved orbit, right, uninvolved sides; A,B: entire orbits, C,D: nasal orbits. For the nasal orbits (C,D), these measurements represent the mean HU in the orbit, defined as the mean HU in the nasal superior, nasal at equator, and nasal inferior aspects. For the entire orbits (A,B), these measurements represent the mean HU in all aspects of the orbit (nasal superior, temporal superior, nasal at equator, temporal at equator, nasal inferior, and temporal inferior).

Interestingly, there is a similar trapezoid pattern in all four graphs, representing a higher (i.e., less negative) fat density in cases with a final diagnosis of OC. This pattern was observed both in the involved and uninvolved orbits, although it was significant only for the involved ones (P < .001, ANOVA multivariable analysis). Note that the absolute HU values are lower (more negative) for the uninvolved orbits and higher for the nasal values. POC -> POC = initial diagnosis POC, final diagnosis POC; POC -> OC = initial diagnosis POC, final diagnosis OC; OC -> OC = initial diagnosis OC, final diagnosis OC; OC -> POC = initial diagnosis OC, final diagnosis POC